-->''The fiercest serpent may be defeated by a swarm of ants.''
-->--'''[[FourStarBadass Admiral Isoroku Yamamoto]]''', discussing the ''Yamato''-class battleship.
----
[[foldercontrol]]

[[folder:Watercraft]]
* The real life USS ''Enterprise'': ''Eight. Nuclear. Reactors.'' They figured this one out before they built another one, fortunately. Why eight? Conventional large aircraft carriers have eight boilers, so logically the "Big E" should have eight ''nuclear'' boilers, right? Also, the size of the boilers matched up nicely with the reactors that the Navy had already been building for submarines, meaning it was much simpler to adapt than to create a massive new reactor (which they later did). After drastic cost overruns nixed the five sister ships she was supposed to have (and resulted in the next two carriers being conventionally-powered), engineers realized that even a ship that big only needed two reactors (though ''Nimitz''-class reactors are much larger and more powerful).
** The Big E is also the fastest carrier in the fleet. Which turned out to not be that useful, because few escort ships (even among the handful of nuclear-powered cruisers that the Navy used to have) were fast enough to keep up.
** USS Enterprise has also the nickname ''Mobile Chernobyl'' because of apparent reasons. She is getting old, and maintaining eight ageing nuclear reactors is tedious.
** And after her retirement, the ''Enterprise'' couldn't even be used as a museum ship like other carriers, due to the danger posed by its aging reactors. The ship literally has to be cut to pieces in order to safely remove all of the reactors. Sadly there just won't be enough left her to make a museum out of. There is, however, talk of saving her distinctive cube-shaped island and placing it on shore for a museum.
* In general, most non-carrier nuclear powered surface ships, though in the 21st century, some have argued that nuclear cruisers and destroyers might actually be cost-effective in an era of extremely high oil prices. Gas turbine-powered vessels are, generally speaking, much more efficient than steam-powered (even nuclear steam-powered) ones due to their higher operating temperatures; carriers only get a pass in this regard due to the need for steam to power their aircraft-launching catapults. And to a lesser extent, because not having to carry any fuel oil for the engines means more room to store jet fuel and/or munitions for the aircraft.
* First-rate ships of the line during the era of WoodenShipsAndIronMen were 100-120 gun monsters with 800 strong crews and which weighed in excess of two thousand tons. Whilst they were terrifying effective in their intended role: to stand in the line of battle and engage enemy fleets in pitched sea-battles, they were effectively useless for anything else, and could not be send out alone as even a pair of well-commanded frigates could outmaneuvre one. They were also fiendishly expensive to operate. When not at war, the Royal Navy generally only maintained less than ten ships of this class, usually as flagships for the various fleets. The rest were kept "in ordinary" - tied up at port with skeleton maintenance crews, and which would then be re-commissioned as the strategic situation demanded.
* The Spanish ship Nuestra Señora de la Santísima Trinidad, a ship [[UpToEleven larger than the already massive first rate ship of the line]]. For comparison, here is [[http://www.hnsa.org/ships/img/victory1.jpg HMS Victory.]] The Santísima Trinidad carried 140 guns, compared to HMS ''Victory's'' 104. It was so huge that it crawled at a snail's pace (and was nicknamed ''el Ponderoso'' (The Ponderous) as a result). So many men were required to man it that its supplies ran out very quickly unless it was near a friendly port. The Santísima Trinidad only saw battle twice: Cape St Vincent where it ended up surrendering without doing any damage, but the Spanish ships ''Infante Don Pelayo'' and ''Príncipe de Asturias'' managed to reach and secure her before the British, and [[CurbStompBattle Trafalgar]], where it was battered into surrender by the more maneuverable HMS ''Neptune'' and then later scuttled by the British in a storm due to its high center of gravity. It was AwesomeButImpractical incarnate.
** The US Navy had the USS ''Pennsylvania'', a four decker of 140 guns and physically larger than the ''Santisma Trinidad''. It was authorised in 1816, laid down in 1821, and... launched and commissioned in 1837. The HMS ''Victory'', for comparison, took only six years to complete (then spent twelve years in ordinary until finally commissioned during the Revolutionary War), while the HMS ''St Lawrence'', of 112 guns and the only first rate in the Great Lakes, was laid down in April 1814 and completed and commissioned in ''September 1814''. The ''Pennsylvania's'' only voyage was in 1837-8, from Delaware Bay to Chesapeake Bay, and was finally burned in 1861 to prevent her capture by the Confederates.
* Before the ''Santísima Trinidad'', there was the Swedish ''[[http://en.wikipedia.org/wiki/Vasa_(ship) Vasa]]'', at its time the largest warship in the world. In 1628, on its maiden voyage, it majestically left its berth, and majestically.... sank before even leaving the Stockholm harbour.
** Vasa had a crucial design failure. Her metacentric height was far too low. The design of her sister ships were altered immediately after the accident: to have wider beam and more freeboard.
* The ''Yamato''-class superbattleships of the WWII Imperial Japanese Navy. Wielding the largest guns ever placed on a warship, an incredible amount of armor, and (eventually) a punishing collection of hundreds of anti-aircraft guns, they were meant to be the superweapons that would issue the killing blow against a belligerent (likely United States) naval force -- after the IJN's carrier and submarine force had softened it up. Unfortunately for the IJN:
** The rapid advance of aircraft and aircraft carrier technology during ''Yamato'''s construction war eventually made it clear to the IJN that they could not risk the ''Yamato''-class ships against the US Navy until its island airbases and carriers had been totally wiped out by the IJN. But by the time ''Musashi'' had launched in August 1942, the USN had annihilated the IJN's carrier fleet at Midway and was only a few months away from launching its own ''Essex''-class fleet carriers. At the end of the first year of the Pacific war, it was obvious that the essential prerequisite for fielding the superbattleships - the total destruction of the US carrier fleet - was never going to be met.
** Even if the "decisive battle" the IJN hoped for actually occurred, the superbattleships weren't necessarily the best tools for the task. Despite their massive size and armament, the superbattleships just didn't have the level of technology and survivability one would expect for a ship that required such a tremendous amount of resources to build and operate. There is evidence that the construction of these ships actually damaged the Japanese economy; the curtain woven to conceal Yamato's construction from prying eyes required so much rope it crippled the Japanese fishing industry.
*** Although the superbattleships were reasonably speedy for their incredible size, they were still much too slow to operate alongside carriers, and consumed massive amounts of fuel. As a result, in the few instances they risked leaving port, they tended to operate as a separate "Main Force" - so distant from their carrier strike force that they may as well not have left port to begin with. One key instance of the speed problem was during the Battle of Guadalcanal where the Japanese forces on the island could have benefited from extra fire support from the battleships. Unfortunately for them, the only battleships in the Japanese Navy that could operate economically were the four old battlecruisers that ''predated World War I''. All the other battleships, including the Yamato and the Musashi, either burned up too much fuel or were too slow to effectively support their ground operations. And before long, American battleships gave a reminder of what happens when battlecruisers fight battleships; had Yamato and Musashi been built as smaller but faster ships, the outcome could have been very different.
*** The steel armor available to Japan wasn't of the same quality as that in the United States, so despite its incredible thickness it was still vulnerable to the USN's "super-heavy" model of 16-inch armor-piercing shells. Its own 18-inch armor-piercing shells, likewise, were only about as effective as the USN's 16-inch shells. Thus, its guns and armor were comparable to the USN's ''Iowa''-class, even though the ''Iowa''s were about 2/3 the weight of the ''Yamato''s and fast enough to operate alongside carriers.
*** Although the IJN excelled at naval gunnery at the start of the war, the accuracy of their manpower-intensive fire control systems deteriorated rapidly under actual combat conditions and had problems tracking maneuvering targets or compensating for evasive action. Since most surface engagements were short, sharp battles that took place at short range at night these shortcomings were neither apparent nor material for most of the war. The IJN did not develop or install new fire directors and radar as rapidly as the USN, and never developed anything close to the Mk I fire control computer that US Battleships carried. So despite the massive range of the 18-inch shells, they could not match the accuracy of US guns even at the beginning of the war, let alone the radar-guided gunnery many USN ships were fielding by 1944. Yamato's poor gunnery at Samar was as much due to crew exhaustion from the repeated air and submarine attacks she'd experienced in the previous 48 hours as it was to the difficulties in tracking small maneuvering targets with her huge turrets while taking constant evasive action.
*** Damage control doctrine of the IJN was lacking, which meant any damage the ships absorbed could not be repaired as rapidly, and certain types of damage had the potential to cause a [[DisasterDominoes cascade of failures]]. By using resources that could have built several capital ships to instead build one very large capital ship, the IJN compounded this issue.
** And finally, not to put too fine a point on it, the value of the superbattleships is evident in their abysmal performance during the war. The ''Yamato'' engaged US surface ships in only one engagement, the Battle off Samar, where (despite ''weighing more than the entire force she opposed'') failed to score a single confirmed hit on an enemy ship.[[note]]Based on the confirmed hits by other Japanese battleships at Samar, it doesn't even matter if she got any hits in because her armor-piercing shells would likely have passed through one side and out the other of the unarmored destroyers without enough resistance to set off the fuse and explode.[[/note]] The ''Musashi'', meanwhile, was sunk by aircraft prior to the Battle off Samar, and never fired a single shot at an enemy surface vessel in the entire course of her career. In the end, neither ship ever came into gun range of an enemy capital ship. And those hundreds of AA guns were underpowered and obsolete even before they were installed, serving mainly to increase the number of men who went down with each ship.
** Other examples of the Awesome Yet Impractical nature of the ''Yamato'' and ''Musashi'': their guns were so powerful that the ship's boats could not be left out on deck while the guns were fired. Special hangers had to be incorporated to store all the boats, which was one more added cost and also meant they carried fewer boats than would be expected for such mammoth ships. And fewer boats to load the crew into is a problem if the ship, you know. Sinks. Likewise, the ship's crew could not be outside on deck either when the guns fired, because the concussive force would literally knock them unconscious. And [[TheNudifier potentially rip their clothes off their bodies]]. This proved even more problematic when it became clear that even the largest, best-armored battleship is extremely vulnerable to air attack and thus the IJN had to find a way to put lots of anti-aircraft guns on deck without them being damaged by the main guns' blast.
* As WWII went on, the Japanese Navy, who carefully crafted the best aircraft carriers and accompanying naval airpower the world has ever seen over the 1920s and 1930s, found themselves scrambling to make good the loss of four fleet carriers and hundreds of air crew over the course of 1942, and the substantial wartime production of US carriers. In desperation they put forth a few new carrier designs into a rather brutal testing environment - that is, if any inadequacy was found, it would be when they engaged the enemy and sank.
** The first fleet carrier the Japanese launched during the Pacific Campaign, the Taiho, was the largest carrier in the fleet, had a fully-armored hull and flight deck (similar to UK designs at the time), and (like most Japanese carriers) two hangar decks. However, she was prone to mechanical problems, and eventually exploded and sank because a damage control error after a torpedo hit in the Battle of the Philippine Sea flooded the ship with gasoline fumes. Of course, one of the reasons the IJN hadn't used armored decks before was that the ship was the difficulty of giving the ship enough stability and freeboard while maintaining two hangar decks...
*** And the fully enclosed hangar deck made it harder to vent the fuel vapor out, which was also exactly why the Japanese didn't originally adopt such designs earlier...
** One of the ''Yamato'''s sister ships, the ''Shinano'', was converted into an aircraft carrier. While it seemed like a good idea - heavy armor, very torpedo-resistant, lots of protection for the magazines - the very reason carriers (even today) have very little armor is to maximize speed and hangar size. The ''Shinano'' was thus too slow and carried too few aircraft to be a fleet carrier, and instead was intended to be a nigh-unsinkable aircraft carrier tender. But by the time the ship was ready to be launched, Japanese shipyards were under constant threat of air attack, and its waters were swarming with enemy submarines. In a desperate gamble to protect from the former, the ''Shinano'' was sent into the maw of the latter, and steamed to its fitting-out base while still under construction. Its inexperienced crews were unable to save her when it took four torpedoes to the hull, with its watertight bulkheads untested (turns out they were rather leaky) and most of its damage control systems yet to be installed. It was only about a month away from completion when this happened. Regardless, even if it had entered service, it wouldn't have made much of a difference as Japan was still flying more or less the same aircraft it did at the start of the war. And had too few aircraft and even fewer qualified pilots still alive anyway.
** After their defeat at Midway, the Japanese were desperate to put more Carriers to sea to compensate for their tremendous losses. One of these measures was to change their two Ise-class Battleships into hybrid [[TheBattlestar Battleship-Carriers]]. It turned out to be a colossal failure as they didn't have any available planes and pilots to equip the two ships after their conversion process was completed. To top off how foolish this decision was, even if they did have the pilots on hand, the only planes they would've been able to carry were FLOATPLANES (slower and bulkier than a normal plane).
*** Not to mention taking out two perfectly good battleships that could have done some good in battle for extended periods of time.
** On top of that, there was also a secret project to build submersible aircraft carriers, which would be used to stage surprise attacks on the American mainland. Two working submarines were actually built (a third was completed after conversion to a tanker submarine), but the biggest problem was that they could only hold three planes each, which meant any damage they could have dealt would have been negligible, assuming they were able to get past any sort of alert Antiaircraft defenses or fighter patrols. While the I-400 class were an impressive technical achievement given the available technology, they weren't actually ''useful'' for anything.
* Battleships in general, at least eventually. There's still debate over exactly when the battleship became obsolete (The rise of air power? Modern anti-ship missiles?), but it did. And when those weren't a large concern for the US Navy (e.g., off the coast of Lebanon or the first Gulf War, where the 16-inch gunnery of ''Iowa''-class battleships proved very useful), they were still impractical for being extremely expensive to operate and manpower-intensive. However, on account of their awesomeness, all four completed ''Iowas'' are currently preserved as museum ships: ''Iowa'' at UsefulNotes/LosAngeles; ''New Jersey'' at Camden, UsefulNotes/NewJersey (right across the Delaware River from UsefulNotes/{{Philadelphia}}, where she was built); ''Missouri'' in Pearl Harbor, UsefulNotes/{{Hawaii}}; and ''Wisconsin'' in Norfolk, Virginia.
** Additionally, the ageing of the battleship fleet and lack of replacement meant that by the end of the 2000s, they shared literally no systems with new ships coming off the ways - steam turbines have been replaced fleetwide with diesels (most support ships), gas turbines (combat ships and some support ships) and nuclear power (aircraft carriers), the modern Tomahawk missiles are built for a different carrying system (the battleships used an armored box launcher that was phased out in the mid-90s, modern ships use a vertical launching system), their 5"/38 secondary guns used completely different shells than new destroyers' 5"/54 and 5"/62 guns; the 16" guns were completely unique, and new ships didn't even carry the Mk 15 Vulcan Phalanx gun, replacing it with new RIM-116 Rolling Airframe Missile launchers. Additionally, room (and weight) would have to be found for the networking equipment required to work with other ships in the modern Navy. These old ships were struck from the Navy List in 2009, so they will likely never put to sea again.
** The military function of battleships (killing enemy ships of all lesser capabilities without them being able to do anything about it) was taken over by the aircraft carrier pretty as soon as it became feasible to build proper fleet carriers, presumably right at the close of WWI. It did, however, take rather a lot to convince some of the Admirals of this. A carrier can't engage a battleship under all conditions - e.g. bad weather, trapped in restricted waterways - but so long as a carrier is free to manuever and keeping situational awareness, it can keep itself well out of range of an enemy battleship while hitting it with as many aircraft sorties as required to sink it.
* On the topic of Battleships, many battleships of the Pre-Dreadnought era and the early years of the Dreadnought era had some of their guns in an off-set arrangement (for example, the ''en echelon'' arrangement used by the USS ''[[http://en.wikipedia.org/wiki/USS_Texas_(1892) Texas]]'' and USS ''[[http://en.wikipedia.org/wiki/USS_Maine_(ACR-1) Maine]]'' in the 1890s, or the staggered arrangement of the HMS ''[[http://en.wikipedia.org/wiki/HMS_Neptune_(1909) Neptune]]'' in the early 1900s). In theory, this allowed for maximum amount of firepower fore and aft, in addition to being able to fire the entire main battery in a broadside. In practice, the off-set guns couldn't be fired fore or aft without risking damage to the ship's structure due to the off-center force of the recoil, and if fired in broadside, the guns on the far side could damage the deck or superstructure of the ship due to the heat and force of the cannons firing. Which is exactly what happened to the USS ''Texas'' at [[UsefulNotes/SpanishAmericanWar the Battle of Santiago de Cuba.]]
** Similarly, the earlier examples of Superfiring main batteries (where one turret is placed to fire over the top of another turret, also seen on the HMS ''Neptune'' mentioned above) avoided the structural problems with off-set turrets, but the heat and blast (not to mention the hot gasses and such) from the upper guns firing could still damage the lower turret in some circumstances (such as the HMS ''Neptune's'' aft turrets, if the upper turret was aligned within 30 degrees of the stern of the ship.)
** Perhaps the most impractical at all, though, was the double turret. That is, one turret with another turret mounted literally on top of it. In theory, this allowed more guns to be mounted while taking up less space. In practice, the top turret served to damage the bottom turret whenever the it was fired, and to weaken the bottom turret's armor simply by existing. It also complicated the ammunition supply, as mechanism had to be included for carrying two sizes of shells (for the main guns on bottom and secondary guns on top) through the same turret.
* [[AwesomeMcCoolName Battlecruisers]]. Combining the speed of a cruiser with the firepower of a battleship, they were designed to hunt down enemy cruisers, and were effective in that role. Unfortunately, the combination of speed and firepower made it tempting to use them in place of battleships... a role which quickly exposed the light armor that enabled them to have that combination of speed and firepower. Such matchups were a case of GlassCannon versus LightningBruiser. The [[ExactlyWhatItSaysOnTheTin fast battleship]] solved this problem, but they were spectacularly expensive, even by battleship standards.
* The People's Republic of China's ''Kuznetsov''-class aircraft carrier ''Varyag'', purchased from Ukraine. As one Chinese officer was quoted, "All of the great nations in the world own aircraft carriers -- they are symbols of a great power." But whether China will able to operate an aircraft carrier as an effective weapon of war, as opposed to just a symbol of prestige, remains to be seen. The United States Navy has nearly a hundred years experience in carrier aviation, something that can't easily be matched overnight. China is attempting to jump straight from what amounts to a coastal-defense force (albeit a very large one, given that China has a lot of coast to defend) to super-carriers, with no prior experience in naval aviation
** The ''Liaoning'' (they finally settled on a name for her) is proving to be quite a drain on manpower and resources, as the Chinese had real possession of her since 2003 (when it first entered Chinese waters), yet officials continually claim that they have a "long way to go" before the carrier becomes fully seaworthy, let alone operational. And indeed, looking at up to date photos of the thing, it's highly doubtful America will be having any competition there, at least for a long while. Fortunately for China, manpower is not something they have any shortage of.
** But then, acquiring that experience is the whole point of having her in the first place. From the outset she was intended to serve as a training and experimental ship, to figure out tactics and train pilots to serve on the newer, domestic carriers. On the other hand, refitting turned out to be much quicker than a lot of people has predicted, and the ship is planned to be commissioned this fall.
*** Commissioning is not the same as declaring a ship seaworthy or operational. For an example, the HMS ''Victory'', Vice Admiral Horatio Nelson's flagship at the Battle of Trafalgar, is still in commission with the Royal Navy, yet it is highly doubtful she will be put to sea any time soon. Same with the USS ''Constitution'' for America, though she has been maintained over the years and can actually sail (usually for ceremonial purposes). That said, only time will tell how effective the ''Liaoning'' will prove as a blue water vessel (much more a carrier), as well as how effectively the Chinese will utilize her.
** The ''Kuznetsov''-class carrier in general is a fairly impractical vessel, as it was built under the Soviet doctrine of being a cruiser first and a carrier second; in fact, the line is referred to as an "aircraft carrying cruiser" in original Russian terminology. To put that in perspective, the ''Kuznetsov''-class has more raw firepower than traditional carriers, which allows them to function as actual attack ships instead of just floating runways, but this comes at the cost of having a smaller carrying capacity than traditional carriers as well as lacking effective means of launching them (a la catapults). In turn, the aircraft carried are normally used in fleet defense rather than frontline action, which the Russians reserve for ground based aircraft. Overall, the ''Kuznetsov'' is something of a go between for carriers and cruisers, capable of performing either type's roles but nowhere near as effectively as "real" carriers and cruisers.
*** Part of the reason for this Soviet doctrine has to do with treaty limits concerning the types of ships that can cross the Bosphorus. A pure aircraft carrier cannot cross the Bosphorus under the Montreux Convention, but a cruiser that happens to carry aircraft [[http://www.mfa.gov.tr/implementation-of-the-montreux-convention.en.mfa can]].
*** The Chinese actually realized this, and have removed the anti-ship missile tubes while completing the ''Liaoning'', thus expanding the hanger capacity somewhat. Russia intends to do the same the next time the ''Kuznetsov'' is overhauled, whenever they get around to doing that. However, both ships are still stuck with the ski-jump for launching their aircraft, which is simpler and cheaper than a set of catapults but limits the payload of the aircraft and also requires them to expend more fuel in takeoff. Converting them to use catapults would be such an extensive modification that building a better carrier from scratch would be a more cost-effective choice.
* [[http://en.wikipedia.org/wiki/Tessarakonteres The Tessarakonteres]] is an [[OlderThanFeudalism ancient]] example from [[AncientGreece the Hellenistic period]]. The largest human-powered vessel ever built, it had 4,000 rowers... and roughly the maneuverability of the Parthenon.
* The [[http://en.wikipedia.org/wiki/Submarine_aircraft_carrier Submarine aircraft carrier]] - such an awesome idea that the Germans, British, French, Americans, Italian and Japanese all pursued the idea. Only the Japanese ever actually built one, though. The Japanese actually built 47 submarines with the capability to carry seaplanes (between one and three, depending on the model). But the aircraft carried were limited in capabilities (with potential strike damage essentially limited to propaganda value), the process of surfacing, launching, recovery and submerging took a lot of time, and the submarine itself was vulnerable to attack while doing so. They were also very large -- the [[http://en.wikipedia.org/wiki/I-400_class_submarine I-400 class]] boats were among the largest non-nuclear submarines ever built. It's still an awesome idea, though... and one which just might have a shot at becoming practical in the 21st century, in the form of submarine-launched [=UAVs=].
** France built an equally impractical ''submarine cruiser'', the ''[[http://en.wikipedia.org/wiki/French_submarine_Surcouf_%28N_N_3%29 Surcouf]]''. It weighed in at over 4000 tons, larger than destroyers of the day, and was armed with a pair of 8-inch (203mm) guns in a forward turret, and a single small seaplane for reconnaissance and spotting for main guns. Its more conventional armament was a dozen torpedo tubes. ''Surcouf'' had a rather unsuccessful career until it was sunk under controversial circumstances during World War II.
** Britain had already done one better than the French in 1917 with the M-class Submarines. Originally designed for shore bombardment, the M-class was equipped with a 12-inch gun that allowed the submarine to attack from a range of 15,000 yards. Unfortunately, the 12-inch gun could only be reloaded when the sub was surfaced and also represented a weak point in the hull which was well illustrated by the accident that sunk the ''M1'': A Swedish ship collided with the M1 which caused her gun to be torn off and created a gaping hole that allowed seawater to gush through. After the accident, M2 was converted into an impractical Carrier Sub and M3 was converted into a Minelayer Sub, meaning it was the only one of the three to have any useful purpose.
* [[http://en.wikipedia.org/wiki/Alfa_class_submarine The USSR's "Alfa" class submarine]]. It set the record (still held to this day) for the second fastest and deepest diving military submarine in the world[[note]]after the preceding ''Papa'' class, itself too AwesomeButImpractical to produce beyond one prototype[[/note]], and knowledge of its production greatly alarmed the West, to the point that the US and Britain both designed torpedoes for the specific purpose of hunting down Alfas[[note]]As for standard torpedoes, an Alfa could just turn around and outrun them. The Soviets specifically tested this by firing torpedoes at their own subs![[/note]]. Unfortunately the Alfa had small and powerful but ''very'' maintenance-intensive lead-cooled nuclear reactors that ''couldn't normally be turned off'', as doing so would let the lead solidify and essentially turn the whole thing into a solid inert lump. Entire maintenance facilities had to be constructed at Alfa homeports simply to keep the reactors hot when they weren't being used - but, in typical Soviet fashion, the facilities themselves weren't properly maintained and often didn't work. As a result Alfa reactors had to be kept running at all times, which they hadn't been designed for and which resulted in several expensive failures. While the reactors could remain active for 15 years they also could never be refueled and were intended to be replaced at the end of their life, like a battery is; despite this the Alfa hadn't been designed with quick reactor replacement in mind, so the process would have been expensive and slow, potentially more than refueling a traditional submarine. In addition, while the Alfa reportedly had a crush depth of over 1300 meters, deep dives did permanent damage to the submarine's onboard equipment, so that impressive diving ability was largely wasted in practice.
** The Alfas were also ''louder'' than other nuclear attack subs of their era, which is a problem since stealth is the main weapon of a submarine. On the other hand all this loudness was mainly during the top speed runs, at cruising speeds ''Alphas'' weren't any louder than other Soviet subs of that generation.
* The ''Seawolf''-class submarine, which was the last Attack Submarine of the Cold war era, was designed to combat the advanced ''Akula''-class and ''Typhoon''-class submarines of the Soviet Navy. Cue the fall of the Soviet Union which led to the ''Seawolf'' becoming so unnecessary (and more importantly, ''expensive''; in today's dollars they'd cost over $3 billion apiece, comparable to the cost of a new supercarrier) that only 3 out of an intended 29 of them were built. The class was an example of a costly political boondoggle, as BillClinton's promise to keep the program afloat in 1992 enabled him to carry the state of Connecticut (Electric Boat, the USA's submarine contractor, is a huge employer in the state) over New Englander Paul Tsongas in the Democratic primaries and ultimately become President. The ''Seawolf'' was succeeded by the ''Virgina''-class attack submarine, which was a less capable blue-water sub, but (in theory) less costly to build due to using commercial-off-the-shelf electronics and lower-grade steel.
** Sadly, the ''Virginia'' class is turning out to be just as expensive as the ''Seawolf'' was. No real savings there, after all, and overall, it's doubtable that either class is an improvement (operationally) than simply building more of the older ''Los Angeles'' class would be, particularly in a post-Cold-War environment. The building schedule and modular construction of the Virginia-class boats does mean they are becoming more cost-effective to build, and will be overall cheaper as the R&D expenses are spread across more hulls.
* [[NazisWithGnarlyWeapons German]] electronic industry of the 1930s was a pioneer of the radar and Kriegsmarine battleships had very advanced radar systems, more accurate than even battleship guns when ranging a ship-sized target, yet none of them had a plotting grid or means to broadcast the radar data to the fire control directors, so each radar range had to be corrected by optics to get a firing solution.
* Italian [[http://en.wikipedia.org/wiki/Vittorio_Veneto_class_battleship Littorio-class battleships]] of UsefulNotes/WorldWarII had greater firepower of anything that wasn't American or the ''Yamato'' (yes, even the famous ''Bismarck'' was badly outgunned by the Italian ships) with the longest-ranged guns of any battleship ''ever'' (and a piercing capability comparable to the much bigger 406mm-caliber guns of the American battleships and the 457mm guns of the ''Yamato''), had an awesome point defense, were 30 knots fast (enough to qualify as fast battleships, and faster than most), and were awesomely armored. Also, the guns were tremendously inaccurate at the long range they were used at (not just due a lack of radar: they remained inaccurate even after the Italians managed to develop and install it) and had short barrel life (due to the excessive velocity) and low rate of fire, the point defense wasn't ranged enough to defend from radio-controlled guided bombs (the only ship of the class to be lost was sunk exactly by a German anti-ship guided bomb. To be fair, not even the Germans had seen it coming at the start of the war), the torpedo defense used an ineffective design more expensive than the conventional (it would have been superior to normal, had the right construction techniques been available and not been compromised by speed-optimized hullforms), and the combination of high speed and thick armor made them fuel hogs, with the fuel shortage suffered by Italy during the war forcing them to stay in harbor for most of the war. Note that this is the ''less impractical'' version: the ships had been originally built with bulbous bows for higher speeds but had been modified due excessive vibrations, and the original design was supposed to use 406mm-caliber guns but opted for smaller 381mm guns because they would have to be designed from the ground up while 381 designs to improve were already available.
** Italian ships of UsefulNotes/WorldWarII in general: as Italian doctrine of the time was geared to fight the French navy, ships other than battleships were built with high reliability, ludicrous speed and thin armour in mind, so that their light cruisers would chase down and sink enemy destroyers and lure enemy light cruisers where heavier firepower was available, their heavy cruisers would chase down enemy light cruisers and lure enemy heavy cruisers in the guns of the battleships (that would have been able to sink enemy battleships from range and avoid counterfire at smaller ranges thanks to superior speed), and their destroyers would simply avoid enemy battleship fire and torpedo them with impunity. While arguably effective against the intended opponent, the Italians never fought the French navy but the [[BritsWithBattleships Royal Navy]], whose more aggressive combat doctrine, combined with higher initiative allowed to British commanders, the presence of carriers and the British ability to consistently break Italian and German codes, and British superiority in radar technology (Italy did not have functional radars when they entered World War II) ended up causing Italian ships to fight with similar-sized opponents again and again, where speed was less a factor than thick armour.
* Similar to the above, the Italia ''Zara''-class cruisers were one of the finest cruiser designs of the second World War: A unique armor layout made them the best protected cruisers until the introduction of the ''Des Moines''-class by the USN, an innovative scheme of secondary weapon placement that made their anti-aircraft defenses extremely formidable, and saved weight meant they were only 2kts slower than the preceding ''Trento''-class, whose GlassCannon tendencies they were designed to address. Indeed, there were no better ships for their intended mission - zooming up and down the Italian coast defending it from French attack. In the Battles of Calabria and Cape Spartivento, they gave the British serious difficulty. All that weigh reduction meant cutting down the superstructure, meaning it was very difficult to mount radar, which in turn meant the ''Regia Marina'' didn't bother (which did not even matter because Italy didn't even have access to radar technology when the ships were being designed anyways). The folly of this decision was demonstrated at the midnight Battle of Cape Matapan: three (radar-equipped) British battleships, the ''Warspite'', the ''Valiant'', and the ''Queen Elizabeth'', were able to close to within 3 kilometres of a flotilla of three ''Zara''s - point-blank range in naval terms - and opened fire, illuminating the Italian ships with their searchlights (the ''Valiant'''s searchlights were commanded by [[TheHouseOfWindsor Prince Phillip]]). Within minutes the ''Zara''s were out of action. They had not even managed to fire a single shot in reply.
* Meanwhile, the Imperial Japanese Navy's post-Washington Treaty light cruisers showed that they were all about this trope. While they pioneered the idea of circumventing the treaty by [[LoopholeAbuse abusing its loophole of defining light cruisers only by gun caliber]] and building what were effectively heavy cruisers with light cruiser guns [[MoreDakka in huge numbers]] (the US Navy and Royal Navy promptly copied this idea) in the form of the ''Mogami'' class, they also insisted on using 6.1-inch (155mm) guns even though the IJN already had ships in service with 6-inch (152mm) guns of nearly identical capability to the new slightly larger guns. Why? Because they were so offended by their government agreeing to the treaty that they required that every treaty-compliant ship have the absolute maximum allowable capabilities. Even when it resulted in complicating the fleet's logistics for no discernible gain.
* There are modern schools of thought that suggest the modern concept of the supercarrier (massive floating airfields with dozens or over a hundred aircraft and thousands of sailors and airmen) is, itself, awesome but impractical for the purposes of naval engagement. While they are powerful political tools and amazing resources for fighting asymmetrical wars (being essentially unreachable by "boots on the ground"), antiship missile technology has matured to the point where even relatively lower-tech countries can afford to just [[MacrossMissileMassacre spam effective anti-ship missiles in such numbers that getting through to such a massive target is virtually certain.]] Additionally, supercarriers and their escort fleets can be easily spotted even from space by their massive wakes and by surface radar.
** Basically, the theory goes that they're already outdated, and there just hasn't been a symmetrical naval war large enough to make this fact apparent. Not to mention the extreme expense that goes into building and operating what is effectively an entire floating city compared to more BoringButPractical measures like simply basing aircraft out of ground-based airfields in friendly territory.
** Much of this has always been true (and has been argued since before WWII), but the problem has been magnified by procurement decisions of the United States Navy over the last 50 years. Most specialized strike aircraft, anti-radar aircraft, anti-submarine aircraft, and everything else that isn't a COD or a helicopter have been folded into the Hornet and Super Hornet programs, sacrificing operating range in order to maintain the two aircraft as supersonic-capable air superiority fighters. The lack of long-range interdiction capability requires carriers to operate closer to land, and within anti-ship missile range. The problem will be magnified in the future, as fifth-generation stealth aircraft are expected to complete the vast majority of their missions on internal fuel, as to not compromise their stealthiness.
*** However, one potential solution is the use of drones, which have over double the effective range of manned aircraft. This is why the Navy is now investing heavily in Northrop Grumman's X-47B, which has been able to autonomously land and take off from carriers.
* The submarine itself was like this for many years. It was slow and often more dangerous to its operator than to an enemy ship (the first successful sinking of a surface warship (the USS ''Housatonic'') by a submarine (the ''H. L. Hunley'', armed with [[RammingAlwaysWorks a Spar Torpedo]]), during UsefulNotes/TheAmericanCivilWar, was followed soon after by the ''third'' sinking of that same submarine). Germany, the last Great Power to build a submarine, was able to demonstrate its capabilities once and for all when, in the opening weeks of World War I, a single U-boat sank three British cruisers in under an hour.
[[/folder]]

[[folder:Landcraft]]
* Double Barrel Tanks are undeniably cool, but:
** The Soviet [[http://en.wikipedia.org/wiki/T-28 T-28 tank]], with Finnish nickname ''Postivaunu'' (Stagecoach). Three turrets, three cannons and up to five machine guns, but horribly unmaneuverable and slow, and easily defeated with improvised anti-tank weaponry. Finnish troops captured seven of these monsters during the war. In the vehicle's defense, it had first been deployed in 1931, at which time it totally out-classed any other extant design. It was simply kept in service well-beyond its effective life.
** The Soviet T-35 heavy tank deserves special mention here; it looked [[ImpossiblyCoolWeapon impossibly cool]], [[MoreDakka had 5 turrets and 6 machine guns]], weighed 45 tons and took 11 crew members to operate. It was also slow, incredibly expensive, and far too mechanically complex for the rigors of war. Only 61 were built, and most of those were lost due to mechanical failure rather then German Panzers. The T-34 was half as big, and only had one turret. This tank won World War II, and 84,000 T-34s were eventually built. Worst of all, the turrets, when aligned a certain way, actually blocked the escape hatches. So, if the tank was hit, the poor bugger crewing it had to ''hand-crank'' his turret out the way before he could bail out - or, if the turret was damaged and unturnable, presumably use his sidearm to shoot himself rather than burn to death.
*** This type of tank was called the "land battleship" and was used by many different armies, such as the German Grosstraktor and Neubaufahrzeug, and the British [=A1E1=] Independent, along with numerous development projects by various nations that never left the drawing board. They were developed in a vacuum between the two world wars, when there was a train of military thought that believed battles between tanks would be like battles on the seas. Hence "cruiser tanks", "battleship tanks" etc. Needless to say, in reality the battles were nothing like that, and all these designs quickly fell out of favour and were replaced by more practical ones. The idea of sticking guns poking out everywhere on a tank may have seemed like a neat and effective idea, but the difficulty a commander faced in coordinating all the guns, the increased crew requirement to man each gun, problems in ammunition management and supply for varying calibres of weapons, and the complexity and cost that multiple turrets and sponsons added to production were ultimately the undoing of the Multi-turret concept. It was finally realized by the latter half of the 1930s that perhaps the French were on the right track after all when they just stuck all the guns onto a single rotating turret for the granddaddy of modern tanks, the FT-17. Even then, the hull-mounted auxiliary machinegun managed to linger on through World War II, but eventually by the end of the Korean War it was realized that drilling a hole into the front armor protecting a tank to stick a machinegun in was an avoidable design flaw.
* What could be more awesome than [[http://en.wikipedia.org/wiki/War_elephant War Elephants]]? Unfortunately, they tend to panic in battle, trampling friend or foe with indifference. During Timur's invasion of India, his forces faced 120 armored Indian war elephants with (for even more awesomeness!) ''poisoned tusks''. In an act of genius, insanity, or both, he ordered all his camels lit on fire and sent the screaming animals towards the advancing elephants. The massive beasts panicked and trampled over their own forces. Timur's army then easily ran down the fleeing enemy troops. Timur then picked up the IdiotBall himself, incorporating the elephants into his own army, perhaps figuring that no one else would figure out his strategy.
** War elephants had been made obsolete in Europe by the Roman ways (yes, ''ways'') of dealing with them, that include such things as ox-driven chariots equipped with ''huge'' spikes to wound the elephants and pots on fire to scare them (these ultimately failed, but [[PyrrhicVictory provoked many losses among Pyrrhus war elephants]]), insane numbers of flaming arrows (scary enough to make Pyrrhus war elephants panic and stomp his own troops), extremely loud horns (that made run part of Hannibal's elephants over his own army) and simple axes. When the Romans started chopping enemy war elephants with axes, their enemies finally got the memo and stopped using them (Parthians and Sasanid made use of war elephants, but never deployed them against the Romans).
** [[HollywoodHistory Despite common depictions of the contrary]], only one of Hannibal's 37 elephants survived the crossing of the Alps and the first battles in northern Italy, and did little more than parading Hannibal around.
** During the decade-long [[http://wildfiregames.com/0ad/page.php?p=7050 Numantine War]] (sometimes nicknamed Rome's [[UsefulNotes/TheVietnamWar Vietnam]]) the Romans themselves got desperate enough to try war elephants and hired a company from the allied African kingdom of Numidia. As they were about to charge before the walls of Numantia, however, one of the local warriors threw ''[[RockBeatsLaser a stone]]'' with a sling that hit one of the elephants in the head (some versions say [[ImprobableAimingSkills right in one eye]]). The elephant panicked, the other elephants panicked in turn, and before they knew it the entire herd was stomping [[HoistByHisOwnPetard the Roman lines behind]]. The Romans never used elephants in Spain again.
** The only real value war elephants have is that something about the smell of elephants makes horses panic, rendering the enemy cavalry worthless near them...unless your enemy knows about this, and has trained their cavalry horses near elephants to get them used to the smell.
*** Horses are also scared of camel smell, making them a far cheaper and more reliable alternative to war elephants.
**** And if you can field enough of them, camels make better mounts than horses for cavalry because camels are faster than horses. Then can also carry troops through arid regions much better than horses, as a camel can go for much longer without needing to be watered.
* The Soviet KV-1 heavy tank and KV-2 heavy artillery tank. They were so heavily armored that they were almost completely immune to German tank fire, while having enough firepower in turn to blow apart concrete structures or punch through German tank armour from a thousand meters away. There are few cases where KV-1 tanks have managed to face off against foes several times their number --in one case, a single KV-2 tank held off an ''entire German division'' for a day. The problem is that they also happened to be too heavy for most bridges to support, and lacked the snorkeling equipment necessary to ford rivers. It also made them very slow and resulted in far more breakdowns than the famous (and far more effective) T-34 tank. And of course, being immune to German tank fire is one thing. Being immune to German aerial bombardment is something else. The large, slow KV-1 and KV-2 were easy targets for Stukas.
** KV's reliability problems were [[SarcasmMode Legendary]]. Out of 600 KVs the Soviets had at the beginning of the war, 200 broke down without enemy contact at all, and another 200 were incapacitated by non-penetrating hits. In the end the Germans hardly noticed KVs at all, whereas T-34 quickly became a major problem for them.
** The vast turret of the KV-2 almost deserves an entry in itself. In order to equip the lethal 152 mm howitzer, the Soviets built a very tall turret for it; unfortunately that made it an almost impossible to conceal giant target. So, to protect the poor bastards who had to lay, load, and fire the massive gun, the Soviets added lots of armor, hoping to compensate for the turret's huge size and lack of sloping. It worked. It worked so well, in fact, that the electric motors installed to turn the turret ''couldn't turn it against gravity'', so the tank couldn't operate at even a slight angle, or the turret would seize.
* The German [[http://en.wikipedia.org/wiki/Tiger_I Tiger]] [[TankGoodness tank]] was infamous for its firepower and protection. Just the merest mention of a Tiger would be enough to panic Allied tank crews, as they were capable of splitting a Sherman Tank in half from over a kilometer away. However, the Tiger was actually something of a white elephant: it was slow, heavy, unreliable, and very difficult to maintain. The fact is that in spite of its vaunted reputation, the Tiger tank was something of a rush job that was pushed through in response to superior Russian tank designs. It broke down a lot and required a full maintenance overhaul every few hundred miles, which often meant sending the tank back to a factory that it just got out of. Furthermore, Germany's deteriorating military situation meant that crucial supplies of nickel, molybdenum, tungsten, and manganese for armor plate were cut off; so the previously excellent German alloy steel was replaced with weakened variants to save on vital materials. This in turn meant that the Tiger's thick armour had an embarrassing habit of shattering on impact, and their tendency to overstuff their guns with propellant in order to make a bigger bang meant that the tank's mighty 88mm gun wore out quickly and had a muzzle-flare that could be seen from miles away. It was also very expensive to manufacture: a Tiger cost somewhere around twice as much as a Panzer Mark IV and over four times as much as a StuG IV assault gun.
** Although the Panther tank was generally a better war machine than the Tiger --it cost noticeably less, was considerably more mobile, and was just as effective against Allied armour-- it still suffered from considerably more reliability problems than the American Sherman tank and was still quite expensive and time-consuming to manufacture. The problem had a lot to do with the fact that the Germans over-engineer their designs, which meant that they were generally built far more complicated than they needed to be. They also spent far too much time and resources trying to make their machines meet 100% of all design specifications, when simply meeting most of them meant that they could come up with a finished product in half the time.
** Incidentally, the Panther's biggest problem came from the opposite of the German tendency to overengineer and overinvest. When the Panthers were being mass produced (especially 1944), the biggest remaining problem was the final drive system, which was notoriously weak. This was because Germans intentionally used cheap, weak parts on the reasoning that the Panthers that were produced would not survive long enough in combat to make use of the more expensive but durable parts uneconomic.
** Meanwhile, the [[http://en.wikipedia.org/wiki/Tiger_II Tiger II]] was a Tiger I doping on bull shark testosterone. It was a bigger, badder version of the already big and bad Tiger I, with improvements including thicker, sloped armor and [[UpToEleven an even more powerful 88mm cannon, the most powerful tank-turret mounted cannon in the entire war]]. However, much like anyone else doping on bull shark testosterone, the Tiger II had some serious performance issues. Because of production limitations due to the Allied bombing campaign targeting German industrial production, the Tiger II's initial drivetrain was from a tank half the size, thus resulting in constant breakdowns that often destroyed the engine completely. It was also fuel thirsty, fuel the Third Reich didn't have. The biggest liability however was the Tiger II's sheer size. Try to imagine just how much of a panic attack a logistics officer had when trying to figure out how to pull a 76-ton tank out of a crater in a bog in the middle of a battle. More Tiger II's were rendered unrecoverable due to mechanical failure and getting stuck in terrain than those that were destroyed. When they were destroyed, it was usually due to being in terrain "lesser tanks" had an easier time negotiating and liberal use of the air superiority that the Allies so enjoyed at that point of the war.
** Although the "Porsche Version" of the Tiger Tank lost to the "Henschel Version", Hitler decided that the "Porsche Version" should be used as the basis for a new Heavy Tank Destroyer which initially became known as the ''Ferdinand'' and was later renamed ''Elefant'' which turned out to be a terribly fitting name for a tank that required ''five'' armored recovery vehicles to tow it off the battlefield if disabled. Early models also had no machine guns, which meant Soviet troops could hide in trenches until the tank passed, and then swarm it with Molotov cocktails. Still, unlike some of Nazi Germany's other designs, this did fit the "awesome" part of the description: at the Battle of Kursk, the 653rd ''schwere Panzerjäger-Abteilung'' claimed 320 Soviet tanks for the loss of only eleven ''Elefanten''.
** Another example was the colossal ''Jagdtiger'', the heaviest armored vehicle used in WWII, which was essentially a Tiger II with a massive 128mm gun mounted in a fixed casemate. On one hand, it's frontal armor was nigh impenetrable and it's gun had a range of over 4 kilometres, and which distance it was still capable of going through a terraced house and destroying the US tank behind it...on the other, everything else about it. It was slow, heavy, unreliable, had a pisspoor rate of fire due to it's unique loading method (which required two men instead of one), and by the time it was employed was easy prey to air attacks.
** The Germans also built the ''Stummoerser Tiger'' or ''Sturmtiger'', an assault gun with a colossal 3.8cm rocket mortar for destroying buildings. 19 vehicles were produced by Alkett and saw action in the Warsaw Uprising. The unit commander reported that the 3.8cm rocketgun was extremely effective. [[GoneHorriblyRight So effective, in fact, that the explosion of the projectile tended to damage the firing vehicle with its colossal blast.]]
** Most of the problems the Germans had with the above designs could have been averted if Hitler had diverted as much resources to logistics as he did to the sharp end. The most critical failure in this regard was the Nazis neglect of armored recovery vehicles. Most modern armies base their [=ARVs=] on the principle that "1 pulls 1": ie, 1 ARV is sufficient to recover 1 main battle tank. The Germans, due to a failure to update their designs, maintained recovery vehicles based on the Panzer IV chassis even as the ''Heer'' switched to Panthers, Tigers, and then on to Tiger IIs. It took ''five'' Bergepanzer [=IVs=] or three halftracks to pull a Tiger or ''Elefant'' out of action, even more for a Tiger II. In some senses, Hitler's neglect of logistics made ''the entire Wehrmacht'' AwesomeButImpractical.
*** Loss-rates for armoured vehicles during offensive operations in WWII average 50-300%, but irrecoverable losses were typically only 20-50% (no new vehicles being added). It is extremely easy to put a vehicle out of action, and thus immeasurably important to have an effective vehicle-repair institution in place. Not losing the ground you fight on is also extremely important, as it means you don't have to destroy your immobilised vehicles to prevent the enemy from capturing them.
* Many heavy tank and superheavy tank designs are prime examples of this trope. They have been rendered completely obsolete by the main battle tank, which combines firepower, protection, and mobility to a much higher degree than any historical heavy or superheavy tank has been capable of.
* Many British and French tanks in the early stages of the war. guns that can kill enemy tanks, check, armour that means enemy tanks can't kill us, check, ability to move above a walking pace, che-no wait, pass. They did have tanks that could go fast too, but most had tin-foil armour. Things didn't get much better until very late in the war, by which time it was over anyway.
* The ball tank, #2 of ''Website/{{Cracked}}'''s [[http://www.cracked.com/article_19914_6-utterly-insane-innovations-history-was-sure-were-coming_p2.html 6 Utterly Insane Innovations History Was SURE Were Coming]] and #2 of [[http://www.cracked.com/article_17366_7-wtf-military-weapons-you-wont-believe-they-actually-built_p2.html 7 WTF Military Weapons You Won't Believe They Actually Built]].
* Tankettes in general. While the idea of a miniature tanks sounds awesome, the reality is that they were impractical for multiple reasons, and phased out during World War 2. Problems included: very thin armour (even hand grenades could pierce it); relatively slow speed (armoured cars were usually a lot faster); very high vulnerablility to infantry assaults (their small size meant enemies could easily clamber onto them); most couldn't mount any weapon larger than a machine gun meaning they were useless against enemy armoured vehicles; lack of a turret - this meant that their guns had a limited arc of fire and range.
[[/folder]]

[[folder: Aircraft]]
* It's 1949, and the US Navy high command is ''pissed''. For nearly two centuries, the Navy has been the lynchpin of US strategic defense, but now everyone is talking about the Air Force, nuclear bombing, and Strategic Air Command. The USS ''United States'', supposed to be the largest and finest (and most expensive) American warship ever launched, as been cancelled 5 days after being laid down. So what do you do? Well, if we can't launch strategic nuclear aircraft from ships, we'll just launch them straight off the damn sea! And so was the [[http://en.wikipedia.org/wiki/Martin_P6M_SeaMaster Martin P6M SeaMaster]] born. A ''transonic flying boat'' to be used as a strategic nuclear bomber. This was in many respects a cutting-edge, extremely advanced aircraft, designed to float on open water, supported by seaplane tenders or special submarines, hopping from place to place and making it hard for the Soviets to find and destroy them. Trouble is, all this brilliant innovation was dedicated to solving a problem that could more easily be circumvented entirely, and it was, with the fleet ballistic missile submarine and the aircraft carrier - suddenly back on the agenda following the [[http://en.wikipedia.org/wiki/Revolt_of_the_Admirals Revolt of the Admirals]] - eventually beating out the [=SeaMaster=] for funding. The program was cancelled as Navy pilots began conversion training to use the new bomber.
** The [=SeaMaster=] as originally designed was even more impractical: it was supposed to be ''ramjet-powered''.
* The B-1 "Lancer" was originally conceived as a nuclear bomber that would roar in at supersonic speeds to defend itself against missiles and enemy aircraft, and would, if hit, eject the entire cockpit as a survival capsule that would parachute to earth. By the time its production version, the B-1B, ended its operational life it was used as a conventional bomber operating almost all the time at subsonic speeds. And no capsule. Ironically, despite it less glamorous mission, the B-1B has become quite effective in its new role, the "Roving Linebacker" for urgent-need air support.
* Some awesome Atomic Age aircraft were rendered impractical not so much by inherent design problems as by advances in missile technologies:
** The [[http://en.wikipedia.org/wiki/XB-70 XB-70 Valkyrie]] was a six-engined high-altitude strategic bomber designed to travel at Mach 3 (which would allow it to outrun Soviet interceptors). All very impressive -- before the development of surface-to-air missiles that could effectively target and destroy high-altitude supersonic bombers. Furthermore, bomber designs like the XB-70 were made obsolescent by advances in intercontinental ballistic missile technology. An [=ICBM=] that could accurately hit a target half way around the world in 45 minutes increasingly marginalized the role of strategic bombers. There was also the huge per-unit costs. To get those impressive Mach 3 speeds, the airframes had to be made of titanium and other expensive metal alloys, making it economically unattractive to mass produce them.
** The [=MiG=]-25 Foxbat was a blisteringly-fast high-altitude interceptor designed to intercept bombers like the XB-70. Despite its short range and primitive but rugged avionics, it might have been effective in that role. But it also had terrible maneuverability and a limited payload (four missiles, no cannon) which made it [[CripplingOverspecialization rather useless when its intended mission disappeared]]. While useful in a reconnaissance role, its combat record (in the service of Egypt, Syria, and Iraq) is poor. And its engines would melt if it pushed to around Mach 3 (what it was ''designed to do in the first place'')[[note]]But that was okay, because the steel leading wing edges made the plane so heavy that by the time it got up to Mach 3 it ran out of fuel anyway[[/note]], eliminating its cost effectiveness as well.
*** The Foxbat did get a limited, short-term use as a propaganda item as it was by far the fastest and highest flying jet fighter at the time (one incident had a Soviet Foxbat in Syrian colors saunter up to an Israeli F-4 running flat out at operational ceiling altitude, let the F-4 crew get a good look, and then accelerate and climb away), but even this backfired when the US developed jet fighters designed to defeat the plane that the US THOUGHT the Foxbat was, namely the ''uber''-successful F-15 Eagle. Then, the US got hold of one through Viktor Belenko's defection in 1976, and discovered all the shortcomings.
*** Its successor, the [=MiG=]-31 Foxhound, is also a pure interceptor, and at first glance looks like a two-seat Foxbat. In reality, it's only loosely based on the [=MiG=]-25, and has a stronger fuselage that allows it to go supersonic even at low altitude. The top speed was dialed back to Mach 2.8 (still very fast, and what turned out to be the top ''safe'' speed of the [=MiG=]-25). The [=MiG=]-31 turned out, despite its limited role, to be far more practical, due to its far superior radar and missiles making it effective against terrain-hugging cruise missiles, not just high-flying bombers.
*** The Foxhound is also seeing a new use in Russian weapons testing, apparently - with their speed, they're perfect chase planes for the Russian military's new planes.
** The [=B-47=] Stratojet had been a CoolPlane, but just the features that made it cool blew the efficiency to hell: the graceful almost Sci-Fi airframe barely had space for a crew of 3 and the wings were thin enough to be flexible in flight, the aerodynamics [[GoneHorriblyRight were so efficient]] that the plane would float over the runway instead of touching down, the superior manoeuvrability mandated the nuclear bomb had to be tossed in a wide looping like a fighter would do in a ground attack flight (less fun when the [=B-47=] weighed almost 100 tonnes at takeoff with full load and maybe 60 tonnes at the point where the ordnance would be released) and the combat range was too short, only 2000 miles or so, shorter than a regular commercial airliner.
** The [=B-58=] [[EmbarrassingNickname Hustler]] was an awesome aircraft for [[TheFifties the mid-1950s]] (it could climb like a rocket and cruise at Mach 2.2 for hours years before the ''parents'' of most Tropers were born), yet it was so breathtakingly expensive to build and maintain (it needed a gigantic belly tank to carry its fuel and just changing a fuselage panel in the field required the specialized jig from the factory to be brought at the airbase) that it was dropped after 10 years in service to be replaced by [=ICBMs=].
* The [[KatanasOfTheRisingSun Mitsubishi A6M Zero]]. Yes it's the most agile thing in the sky and packs a punch, but it tends to blow up at the slightest provocation (compared to the [[BoringButPractical F4F Wildcat]], which could make a Zero empty its ammo into itself and still fly), because all this maneuverability was achieved by lightening the plane to the point that it might as well been made from cardboard. Including the unprotected fuel tanks that spew the flaming gasoline around after the first hit. It still was a tough thing to hit, and only became a true death trap when the US Navy started fielding fighters powerful enough that they could use their high-speed maneuverability to negate the Zero's slow speed agility, namely the F4U Corsair and the Wildcat's successor, the [[TookALevelInBadass F6F Hellcat]], which retained all of the Wildcat's durability.
* The Messerschmitt Me 321. It began its life as a glider, the biggest glider ever made. The mission for this glider was to rapidly transport large amounts of troops and medium or light tanks into the battlefield. The first problem was how to make something that big glide. Thus, it was made largely of hollow steel tubing, doped fabric and wooden spars. Then came actually getting it up into the sky. Normally, a tow aircraft would be used to drag it up into the air, but two towing aircraft would have to do the job, which would be impossible to synchronize safely. The solution? [[http://www.militaryfactory.com/aircraft/detail.asp?aircraft_id=528 They just stuck two Heinkel He-111's together with a third engine between]]. Originally it was intended to be used for the scrapped invasion of Britain, but then was used for Operation Barbarossa. After that, feedback from the people who "flew" them led to a big design change. Sticking six powerful engines on it, they turned it from a glider into the Me 323 transport plane, and it ''still'' needed the damn Franken-Heinkel to take off (or RATO or three airplanes working in sync) if it was fully loaded. It arrived just in time to support Rommel in his collapsing North African campaign. Where they were shot down in droves, because they were slow, ungainly and massive targets loaded with fuel, ammo and other things that went boom. In one famous incident, [[CurbStompBattle 22 were shot down in just one flight]]. It saw service for little under a year before being retired.
* The Convair B-36 "Peacemaker" long-range atomic bomber, which kept the balance of power during the cold war and looked positively badass. When everyone was switching to jets Convair used six huge radial engines - which turned out to be maintenance nightmares, both for their inherent complexity (the ground crews loathed sparkplug replacement duty) and because they were never meant to be mounted in a pusher configuration, resulting in many failures (when your plane losing an engine is considered so routine that ''the mission is allowed to continue as if nothing happened'', you know you have a problem). And for all that the plane was still underpowered, so they eventually fitted four additional jet engines to compensate. The B-36 also featured an innovative control-by-wire system for the engines... but no mechanical backups, so if the electrics failed you were screwed. And the electronics were mounted in delicate housings that would shake themselves apart under the vibrations caused by the turret guns. Even after the design was tweaked and bludgeoned into some kind of functionality, it still had a tendency to spring oil and fuel leaks all over the place or abruptly catch fire. It got retired ten years after its creation, while its Soviet counterpart the TU-95 is still in use today and is predicted to stay in production for ''several more decades''. There again, it could carry ''ten times'' the payload of the famous B-17 Flying Fortress, and its morale and propaganda value was enormous.
** There again, engine failures were less of a problem for the B-36 because its wings were so enormous that the aircrew could actually crawl around inside them and fix the engines in flight if necessary.
** The B-36 was so ''very'' prone to engine fires (mostly caused by excess fuel from air intake icing) and failures that the aircrew soon turned the typical phrase "six turning and four burning", indicating all engines were running properly, into "two turning, two burning, two smoking, two joking and two unaccounted for".
* Fighter aircraft have been getting progressively more complex and more expensive, to the point that a joke got started that pretty soon the Air Force, Navy, and Marine Corps are going to have to share one plane (the Air Force gets it on even days, the Navy on odd days, and the Marines on Feb. 29). The F-35 Lightning II was partly intended to offset this in that it was ''supposed'' to have a much lower unit price tag than the F-22 Raptor. As luck would have it, it ended up being about a third again ''more'' expensive.
** While at the same time not bringing the same capability for aerial combat to the table that the F-22 did, which would've left the US military lacking in aerial combat capability. Of course, it could be said that it already has since the F-22 itself is proving to be plagued with some rather unfortunate problems.
*** It's worse than that - it lacks the air-to-ground ability of fighter-bombers already in use, and lacks the air-to-air ability of the F-22. At this point, it's being pushed ahead more because of an "we've invested so much already we can't stop now" attitude than any real demonstration of success. On the other hand, we don't know if all the onboard computers simultaneously have a stroke upon crossing the international date line as the F-22's did.
* In World War 2, Japan actually deployed balloons to drop bombs. They tied bombs to high altitude balloons that would ride the natural air currents across the Pacific, at which point a built-in timer would release the payload and bomb whatever happened to be below. In a sense, they were successful, being the only attempt by an Axis power in WWII to directly bomb the Continental US that actually ''hit''. On the other hand, the carried bombs were too small and too widely-dispersed to reliably hit anything of strategic value, making them useless as anything other than a terror weapon. A family of six in Oregon killed by one of the bombs are the only known civilian deaths in the US during the war directly caused by enemy action.
** The notorious Unit 731 of the Japanese Army perfected a system to drop Plague-carrying fleas via the same balloons, but the US managed to locate and destroy the launch facilities before it was ready. It wouldn't have really done much damage in the scale of the carnage occurring at the time, but would have been awkward and messy to contain had a Plague outbreak started in a major west-coast city.
** Also, thanks to gag orders and censorship, the US Government was able to keep any news of the balloon bombs out of the press. The Japanese then believed the project was a total failure and scrapped it.
* The B-2 Spirit suddenly lost much of its value as a strategic stealth bomber when the Soviet Union collapsed in 1991. It has since been relegated to rear echelon status and has seen action, as a conventional bomber in only four conflicts: Kosovo, Afghanistan, The 2nd Gulf War, and the Libyan Civil War.
** On the other hand, it does that very well, with an absolutely absurd bomb capacity. Problem being that it's incredibly expensive to maintain and if the computers fail the damn thing ''will'' crash.
* Stealth aircraft in general can be considered this. They're hard to detect with standard engagement (X-band) radar, allowing them avoid anti-air and launch surprise attacks. However, they're expensive to build and maintain. They also have reduced combat capabilities as they carry their weapons and fuel internally. They would also be detected if they use conventional radar or radio (or outgoing datalinks), and are easy to detect with IRST or VHF radar (latter of which however can only be ground-based). While they are great for niche roles like attacking heavily defended command centers, they aren't versatile or practical enough to completely replace conventional planes.
* In the 1980s, the Kamov Ka-50 competed with the Mil Mi-28 to become the next Attack Helicopter of the Russian Army. Although the Kamov was chosen as the winner, budget cutbacks following the collapse of the Soviet Union and the rise of asymmetric low-intensity warfare (Lack of massed armor to target) meant developing a dedicated tank killer wasn't feasible, allowing the Mi-28 to make a come back as the Russian army's secondary Attack Helicopter.
** For that matter, the Soviet Union's first attack helicopter, the Mi-24 "Hind" could qualify. The Hind was modified from the Mi-8 transport helicopter, and still retains a troop carrying capability. It is also heavily armed and armored, making it extremely difficult to shoot down without dedicated anti-aircraft weapons. However, it also has several glaring flaws. For starters, the Mi-24 can't take off vertically if it has a full complement of troops and ammunition, requiring the use of a runway. It also isn't very maneuverable. Part of this is due to the heavy weight of the aircraft, but the design of the hardpoint wings can cause the Hind to [[http://en.wikipedia.org/wiki/Dutch_roll Dutch roll]] and crash. These tend to give the Hind the characteristics of a slow, albeit heavily armored airplane, as opposed to a nimble helicopter. The Hind's armament is also not very impressive. Although modern versions are equipped with a powerful cannon and numerous rockets, it has very limited anti-tank capabilities, using only four anti-tank guided missiles (as opposed to the typical eight to sixteen, depending on mission requirements, of most other attack helicopters). Ironically, the qualities that make it lacking in the sort of armor-rich environment that WorldWarThree would have been make it very useful in the low-intensity, asymetric warfare that became common in the UsefulNotes/ColdWar and post-Cold War period.
* The Messerschmitt Me-262 Schwalbe, the world's first jet fighter. While fast enough to leave any Allied plane in its contrails and an excellent bomber interceptor, its engines were prone to mechanical problems and required high temperature alloys that Germany didn't have enough of. It also required more fuel than the Germans could afford to ration to it. And then, if that weren't enough, [[AdolfHitler some idiot with too much power]] decided the 262 should be a fighter-bomber so they could take the fight to the British Isles again. [[EpicFail Three guesses how that worked out.]] Another problem was that the jet engine relied on mixing two fuels which ignited on contact, which was fine if they only came into contact where they were meant to in the engine, but less than ideal if the plane suffered damage and the tanks leaked or ruptured.
** Too much has been made of the fighter-bomber decision. Hitler was right in believing that the 262 would be the only aircraft capable of penetrating the air umbrella over an Allied invasion fleet, though it wasn't ready in time, and the fighter-bomber issues only delayed production by about a month. And by that point in the war ALL fighters were effectively fighter bombers, as the Allies realized that fighters made effective ground attack aircraft and used them to replace dead-end types like dive bombers. And even if the Me 262 had gone straight to fighter units their primary opponent, the P-51 Mustang, still would have outnumbered them 60-1.
* Around the end of UsefulNotes/WorldWarTwo many rather impressive prototypes of fighter and bomber aircraft had been designed by various American and Russian manufacturers. Innovative uses of old technology (for instance, contra-rotating propellers) made them fast and powerful; sadly, the innovative use of ''new'' technology - namely the jet engine - resulted in aircraft that were even faster and more powerful, but also more efficient and less maintenance intensive. Needless to say, this doomed all the new piston-engine planes into never leaving the prototype stage.
** Related to the above is the turbo-compound engine. It was a late development that used a turbine placed at the end of the exhaust that would recycle power wasted by the piston engine and add it directly to the driveshaft. The engines thus obtained were very powerful and efficient, but were both maintenance-intensive and impractical: the bigger the turbine was the more efficient the engine became, until someone eventually figured out that you might as well leave the piston engine out altogether and simply use the turbine as a turboshaft.
*** The turbo-compound could make a comeback. The problem was it put a lot of stress on exhaust valves which would fail and their shards would take out the turbine. A lot of the power that could potentially go to the turbine was also absorbed by those valves. However, if used on a Wankel rotary engine, which has no exhaust valves, turbo-compounding could potentially make a Wankel engine that runs on automotive unleaded gasoline provide fuel economy and horsepower competitive with turboshaft engines, but without the turbo-lag.
* The jetpack, sadly, turned out to be this. Starting with the Germans in the later years of WWII, several nations attempted to build a practical jetpack for military purposes. (Though contrary to popular belief, the earliest designs were intended for short jumps rather than sustained flight. Enough to bounce over a minefield or quickly cross a river.) And sure enough, many of the designs did work. They were just too impractical. The engines were incredibly loud, they could only fly for a short time (20-30 seconds), and the pilot could get a nasty burn on his legs if he wasn't careful. Ultimately all the military applications jetpacks might have had could be done using easier, cheaper, and safer (though sometimes slower) methods. So while working jetpacks do exist, barring a revolutionary new discovery in small-scale rocket propulsion they are doomed to an eternity as scientific curiosities.
[[/folder]]

[[folder:Artillery, Missiles, and Small Arms]]
* The Nock Volley Gun, a smoothbore flintlock small arm with ''seven barrels'', designed to be fired from the rigging of Royal Navy warships during the NapoleonicWars. Unfortunately, it turned out most men weren't big or strong enough to fire it without a) being thrown violently backwards by the recoil, b) falling off whatever high place they were firing it from, c) having their shoulder shattered, or d) all of the above. It also took freaking ages to reload, even by the standards of the period.
* The Japanese Type 97 20mm Anti-Tank Rifle. Fielded by the Imperial Japanese Army during WWII, and operated by nobody that was sane. The recoil on the Mk-97 was likely to produce the same self-inflicted injuries as the Nock Volley Gun.
* [[http://www.backyardartillery.com/82500 The rubber-band Gatling gun.]] The ''ultimate'' in rubber band small arms technology, it can fire over a hundred bands in a matter of seconds. Unfortunately it costs $500.00 (not including shipping), takes around half an hour to load, has a tendency to jam if not loaded very carefully, and is horribly inaccurate.
* Ironically, the ''actual'' Gatling Gun was viewed as being this when it was first developed, although it has since been VindicatedByHistory. With the UsefulNotes/AmericanCivilWar underway, military quartermasters already had their hands full trying to develop logistical standards for weapons and ordinance. They simply did not want to deal with ''another'' weapon with its own unique set of ammunition and upkeep needs.
* The Gyrojet gun fired rocket propelled bullets and was cool enough to showcase in the Bond film ''Film/YouOnlyLiveTwice''. Rocket propulsion caused problems, though: rather than starting fast and slowing down, it started slow and built up speed. This mean that within a certain range, a bullet would not be moving fast enough to do any significant damage. They were also both more difficult to manufacture and much more expensive then conventional bullets. Finally, air turbulence resulting from the transition from subsonic to supersonic speed effectively destroyed its accuracy. So, lack of power at short range, and lack of accuracy at long range. While later designs have ameliorated some of these problems, they remain more curiosities than practical weapons.
* Actual use of nuclear bombs in war. They make those wonderfully huge explosions, but can't be used anywhere near anything you want to capture, and the strategic advantage gained would probably not be worth the international stigma. (On the other hand, credible ''threats'' of using nuclear bombs can be quite useful.)
** A novel compared the use of a tactical nuclear weapon in war as nothing more than a big cudgel. A tank division gets hit with a tactical warhead, most of the tanks are intact (ground zero was a few miles away), even though the tank crews would die from radiation poisoning in a few hours. The commander immediately realized that they need to immediately prepare for battle. Only an idiot uses a nuke like this and doesn't follow up with a force to secure the area. Sure enough, they quickly spot an enemy tank division on the way.
** Nuclear weapons are the most awesome (in the truest sense of the word) weapons ever created, but practical only for their considerable deterrent and political value, not in terms of strict military utility. Some specific nuclear weapons were even more impractical:
** The [[http://en.wikipedia.org/wiki/Tsar_Bomba Tsar Bomba]] hydrogen bomb took this trope UpToEleven. While massive and impressive in yield, none of the planes in the Soviet air force was large enough to carry it without special modifications, and the bomb's explosion could destroy the bomber that dropped it. It was so large that the bomber that delivered it had to have its bomb bay doors removed and so powerful that even at half the planned power (that is, the output was ''only'' fifty megatons) and with a parachute to delay its detonation the plane barely made it out of the blast zone. Like the Tsar Cannon, it was created for show.
*** Tsar Bomb was more a proof of concept than a real weapon. It was essentially a technology demonstrator designed to ''find'' the upper limit of what was practical. It turned out that it was already too much, but it still made a hell of a PR stunt.
**** The Tsar Bomb as tested had a yield of roughly 50 megatons, and as designed 100 megatons. The design, however, was known as a 'layer cake.' The designed bomb was only one layer, you could add more for increased yield, potentially with no limit. Going above one layer was pointless though, at 100 megatons the size of the fireball would equal the thickness of the atmosphere. Anything more would simply vent into space.
** In a similar category, many American interceptors from the 1950s and 1960s were equipped with nuclear-tipped air-to-air missiles to shoot down incoming bombers. However, the F-101, when used in this role, was so unmaneuverable that if it managed to destroy the bomber, it was guaranteed to also destroy itself, along with both its crew members.
** The [[SuperiorFirepowerTacticalNukes M-388 "Davy Crockett"]] recoilless rifle, formally named the [[http://www.youtube.com/watch?v=im3Hg7Zu-eA&feature=related M65 Nuclear Rifle]], was designed to fire a .01 kiloton atomic weapon a maximum distance of three miles, which left the crew within range of fallout from the bomb. It was a failure as a nuclear launching platform, even in the nuke-friendly 1950s, but come on -- it's an ''atomic bazooka!'' It doesn't get much more awesome than that.
*** The actual nuclear device in the Davy Crockett was the [[http://en.wikipedia.org/wiki/W54 W54]], the smallest acknowledged nuclear device the US ever manufactured. One of the other uses it was put to was the [[http://en.wikipedia.org/wiki/Special_Atomic_Demolition_Munition Special Atomic Demolition Munition]], which was intended for nuking any ground target you might want to attack with a small, hand placed nuke. Yes, that's right, this bad boy was meant to be schlepped in on foot by a soldier (actually two specially-trained US Army Engineers Demolitions specialists, who might go in by parachute, boat, swimming, foot or ground vehicle, depending on the precise target) in a special backpack, then set of with a mechanical timer. Which makes it a nuclear landmine.
*** The W54 was used in the M-338, and had a definitely instantly fatal radiation dose within 500 feet and a probably fatal dose is a quarter of a mile, significantly less than its three mile range. Because of its poor accuracy in testing, it was decided its danger would be its extreme radiation hazard.
** The majority of reasonable sized nuclear weapons are surprisingly '''inefficient''' as battlefield weapons. Two examples: 15-20 kiloton nuclear weapons could not sink at first hit large cruisers like ''Prinz Eugen'' or battleships like ''Nagato'' while classic naval guns could, and later megaton-sized strategic weapons could not be guaranteed to destroy a city or a large military force at first hit (in fact, nuclear strategists estimate that in a nuclear hit large city 80% of the population and 95% of major buildings and assets will survive in a reasonable state, so there is always the possibility for them to retaliate furiously). The actual use of strategic weapons is the "countervalue attack", destroying the industrial facilities needed to sustain civilian life, as opposed to military industry which can be built in protected, underground or fortified areas.
* Other types of [=WMDs=] fall victim to this as well. If you use chemical weapons on the battlefield, you automatically allow counter use... and there are a LOT of countries with covert or open stocks of chemical weapons. The standing policy of the United States (which no longer has chemical weapons in its arsenal) is that any WMD attack will be responded to in kind - i.e., with ''nuclear'' weapons, the only [=WMDs=] America still has.
** Of course, that doesn't mean the US isn't willing to allow their allies to use chemical weapons themselves. During the Iraq-Iran war, the US supplied Iraq with chemical weapons, and gave them the intelligence and equipment needed for Iraq to unleash Sarin Gas on the Iranians.
* The third type of [=WMD=] that has been developed, biological weapons. All sides had operational weapons before the end of WWII (anthrax for the US weapon, and Plague-bearing fleas that could be dropped from a bomb casing for the Japanese one). These ''theoretically'' might have been more devastating, and certainly anthrax could have been more persistent, than the nukes actually used. However, in practice they proved to be absolutely unreliable, as the stresses and conditions of ''deploying'' them tended to kill both the vectors (such as infected fleas) and the disease microbes themselves. And even in the cases when the weapons were successfully deployed (like Japanese did in China), they usually managed to devastate a couple of villages at most. And the strict wartime quarantine measures, available under martial law, were later shown to be very effective in successfully stoppping the epidemic, negating the very reason of the weapon's existence. US learned this from the captured Japanese scientists after the war, and quickly abandoned the concept. Soviet Union toyed with the idea longer, up to the very end of the UsefulNotes/ColdWar, trying to overcome these shortcomings, but without much success.
** Also, unlike conventional weapons, there's often going to be a chance that the disease will spread to your own soldiers or some neighboring allied country[[note]]then there's the political issues that make the use of biological weapons even less practical[[/note]].
* Going cyclic. Dumping your magazine with fully automatic fire is seldom good for anything other than making a lot of noise. It's useful in some situations for suppressive fire, such as when the unit is at risk of being overrun, necessitating dumping as many rounds as possible downrange. With weapons not placed on some sort of mount or chassis, it's a great way to waste most shots after the fourth into the wild blue yonder at anything beyond short range. Not to mention overheating and jamming your weapon which can potentially lead to a catastrophic failure.
** Standard NATO practice is to almost always use only semiautomatic fire. Makes one wonder why they bother with installing the burst fire and full auto capabilities to begin with.
** The Soviets, however, found it more cost-effective to just ''train'' soldiers to fire in short bursts.
* The first iterations of the Sidewinder heat-seeking missile. So strong was the belief in this technology that many NATO fighter and interceptor designs of the 1950s and 1960s era were missile-only (completely without guns.) However, in the Vietnam war, pilots of F-4 Phantom II's equipped with Sidewinders only would sit and watch with frustration as the missiles would fail to launch, launch but miss the enemy airplanes completely, or switch tracking the heat of the enemy's jet exhaust for the heat of the jungle and scream into the ground. The Vietnamese--whose [=MiGs=] had cannons--could just get in close and blow them out of the sky. While later versions of the Sidewinder were much more effective and reliable, this experience led to almost all future U.S fighters and attack aircraft being equipped with guns.
** The Air Force equivalent of the early Sidewinder, the AIM-4 Falcon, was no better. The AIM-4's seeker had a wider field of view than the Sidewinder's - but unfortunately it was too wide; the Falcon could lock on to targets that it couldn't maneuver to hit and lacked a proximity fuse, meaning that it required a direct ''contact hit'' of an enemy aircraft. The on-rail nitrogen bottle that cooled the seeker heads of the Falcons mounted on the Air Force's F-4D Phantom IIs was also considerably smaller than the Sidewinder's, allowing a much shorter useful time window for its seeker. Several influential USAF pilots hated the Falcon and agitated for a return to the Sidewinder, and an improved version of the Falcon, the AIM-4H, was refused by the Air Force in favor of the AIM-9E, and the Sidewinder remains in service to this day.
** One of the first radar guided air-to-air missiles, the Sparrow. While use of radar guidance gave it longer range than the Sidewinder, its first use was too cumbersome: before the invention of the HUD, the pilot had to look down his cockpit (and thus take his eyes off his outside view) into a small screen to aim at his target. Worse, unlike the Sidewinder (and the Sparrow's successor, the [=AMRAAM=]), the pilot had to keep his plane's radar pointed to the enemy until impact, which made him a sitting duck (the [=AMRAAM=] used its own internal radar to maintain guidance, making it a "fire-and-forget" weapon like the Sidewinder). Finally, such long range at the time without Friend-or-Foe identification systems meant you couldn't see your enemy, and thus confirm if your target was really the enemy. Ultimately the Sparrow was relegated to the role of a [=SAM=] as the Sea Sparrow. And while Sidewinder achieved probability of kill between 15 and 20%, radar-guided missiles in Vietnam achieved Pk of no more than 10%. They had same problems with clutter as Sidewinders did, but were larger, less maneuverable and less mechanically reliable.
* Project Thor, aka "Rods From God". A platform in orbit firing kinetic-energy projectiles at targets on Earth. Sounds awesome, right? Well, not so much:
** It takes about 15 minutes from firing to impact, but about 50 minutes (on average) to target.
** Everyone would know exactly where a launch platform is at any instant, what it could possibly hit, when it fires, and once it fires determine very quickly what it's firing at.
** Due to the plasma sheath that forms around a projectile entering the atmosphere, the projectile can't use sensors to retarget itself.
** Finally, the dealkiller: the amount it would cost in money, energy and resources to put enough weapons platforms and projectiles in orbit to make Project Thor effective as a weapon system would buy more than enough existing and conventional weapon systems and launch platforms (which have more flexibility) to make project Thor utterly pointless to have, except when conventional weapons can be easily shot down or fooled by countermeasures.
** Plus, isn't there a treaty that bans weapons in space?
*** Thor would be technically legal, as the treaties that cover weapons in space are pretty specific (Conventional Weapons Allowed. Weapons of Mass Destruction, including Nuclear, Chemical, or Biological, are not allowed).
** To be fair, the Thor was to be used against hardened, heavily fortified targets that wouldn't be moving anyways, but then you could probably just drop a bunch of bunker busters on it faster and cheaper.
* The AN-94 assault rifle, originally intended to replace the AK-74 as Russia's general issue rifle. It is extremely accurate thanks to a 2-round burst system that puts out both bullets before the recoil even affects the shooter's aim. However, it is prohibitively expensive and its internals are much more sophisticated than the AK-74, relegating it to Special Forces use.
* The VSS Vintorez Russian sniper rifle. Its built-in suppressor makes it nearly silent, and its 9mm rifle round hits hard enough to pierce concrete and body armour, despite its suppressor-friendly subsonic speed. However, said ammunition is heavy and rarely issued in the Russian military, it has a prohibitively short range for a designated marksman rifle, and it's extremely expensive. On the other hand, it ''was'' explicitly designed as a special forces rifle, unlike the AN-94. Its primary intended purpose is for urban operations, in which its optimum range of 300 meters or less is more than sufficient since in a city it'll be a rare event to get a shot at longer ranges.
** The VSS can take proprietary 10-round magazines or 20- and 30-round ones made for its brothers, the AS Val and SR-3 Vikhr. It is almost always used with 10-round magazines because, with a magazine any larger, it would be impossible to aim and fire from a prone position without giving oneself away.
* The German [[http://en.wikipedia.org/wiki/Dora_gun Schwerer Gustav and Dora Gun]] were railway siege guns, and the two biggest artillery weapons ever. Designed specifically to destroy France's Maginot Line forts, the guns weren't ready at the time of the Battle of France, which at any rate ended up completely bypassing the fortifications altogether thus eliminating the need for the guns in that campaign. The Schwerer Gustav was used to very good effect in the siege of Sevastopol, but only fired 48 rounds before wearing out its barrel. The Dora was only deployed briefly against Stalingrad, but quickly withdrawn when Soviet encirclement threatened.
** These guns were also awesomely impractical when it came to manpower. It took the equivalent of an entire regiment just to man, move, fire and maintain one single gun.
** In a sense though, Gustav and Dora were actually practical in that they were in effect the only weapons ever created that could breach some of the targets they were used against, in the case of the siege of Sevastopol. Many targets within the city such as the White Cliff ammunition magazine underneath Severnaya Bay were literally immune to any other weapon, and had those targets not been destroyed the siege of the city might have taken even longer then it had, tying up the Germans for a greater period of time and contributing to a hastier collapse. Think of it like this, what's more helpful to you when you need to tighten a bolt: A big expensive wrench that fits the bolt, or a bunch of small inexpensive ones that don't? While the situations where the 80cm guns were of use were limited, they did exist and there was a military requirement for a gun that could penetrate such massively hardened targets, and while Gustav and Dora were expensive and required a great deal of time and manpower to manage, they did ultimately do those jobs adequately.
** The Dora is vindicated in the first ''Literature/{{Worldwar}}'' novel by HarryTurtledove, where it's used to take out two LizardFolk starships parked in Ukraine (one of which just happens to hold most of their nukes). The thing only manages to fire two shots, though, before being blasted by the lizards' air force. It doesn't help that it takes about 30 minutes to reload.
** The railguns were also so large they couldn't use existing rail lines when emplaced, unlike normal railway artillery which could either pivot on its carriage or would simply use an area where the rails curved and move forward or backwards to adjust the aim horizontally. Custom rails had to be built wherever the guns had to be set up, using dual sets of tracks in a curve. When broken down for transport, the gun was moved in a train of 25 cars length on conventional tracks.
* The V-2 rocket, a single-use weapon that cost a fantastic amount of resources per shot, and, thanks to careless use of slave labor, still the only weapon that killed more people on its own side than enemies. [[FridgeHorror But since the slave laborers were also considered enemies it still sorta worked from the Nazis perspective]].
** The main problem was the guidance system, which often failed to hit any of the Britain Isles, if it didn't crash into a German town first.
*** Later it turned out that the guidance system ''design'' was basically pretty sound — the missiles lack of accuracy were largely the result of [[HeroicSacrifice the deliberate sabotage of the concentration camp prisoners]] that built them. Boris Chertok, a Soviet rocket scientist and influential chronicler of the SpaceRace, who worked at their Mittelwerke production site shortly after the war, noted that the workers learned to make the unreliable solders and other parts that looked and worked fine on the initial inspection, but basically shook themselves apart due to stresses and vibrations during the flight. Another issue was that the German spy network in Britain had ''all'' been converted to double agents by the British, so when V-2s would land accurately, they would often send back false reports to Germany that the missiles weren't aimed far enough, causing the Germans to "correct" the problem and end up overshooting.
*** Another problem was the decision to steer the missile by the "gas rudders" — graphite vanes placed into the nozzle that directed the exhaust flow. These were fragile and unreliable all by themselves, and were quickly replaced by vernier engines of pivoting (gimballing in the engineering parlance) the whole combustion chamber and nozzle assembly together both on the Soviet and the American designs.
**** As if all this wasn't enough, the V-2 was intended as "Vengeance" for Allied bombing and so it was fired primarily at London, rather than at the Western Allied beachheads in France, which were often chock-full of vulnerable supplies.
** The V-2's big brother, the A9 - which, fortunately, never left the planning stage, though it did come worryingly close to actually being prototyped - was '''much''' bigger, and intended to strike the US after an intercontinental flight. It would have been so expensive as to make the V-2 look like a bottle rocket in comparison, especially as it would have required an even more massive booster stage to get the required range. Such a booster, the A10, would have used six V-2 engines. The engineers realized that if they couldn't get precise targeting from V-2s there was no way it could be achieved over such long distances, so it was decided that the second stage would be manned. The pilot, had he managed to eject, wouldn't have had much of a chance, as he'd be parachuting into enemy territory. The Nazis even built test sites for this behemoth, but none were ever produced.
** And then there was the A11, which was intended as yet another stage for the A9/A10 combo, and would have used ''thirty-six'' V-2 engines. This three-stage monster was intended to target Japan, but the technology of the time would have limited the payload to... 300 Kg. For comparison, UsefulNotes/WW2-era general-purpose aircraft bombs - certainly capable of causing serious damage, but of little threat singularly - commonly had a weight of 500Kg, and often more. So Germany would have expended huge amounts of fuel, metal and man-power to deliver a payload that would have, possibly, destroyed one or two buildings. Nor did Germany, which was at the time ''allied'' with Japan, have any actual desire to attack them. Not surprisingly, this one didn't even leave the drawing stage.
* The V-3 artillery cannon, which was a massive 130 meter long cannon originally designed to bombard London from across the English Channel. While the gun could actually be fired, it was horribly unreliable since it used a series of controlled explosions to propel the projectile instead of a single explosion. This also made the gun prone to exploding, which is what destroyed the prototype. The guns also could not be turned or moved in any way, though given that they were intended to fire at cities (which by definition also cannot be moved) this was considered unimportant, but it meant that the V-3 guns were incredibly vulnerable to air attack. The intention was that the V-3s would fire 24/7, each one landing a 140kg shell in London every 12 seconds. While each individual shell wouldn't do much damage, an actual sustained bombardment would have completely shut the city down since it would never be safe to leave the bomb shelters. In practice, they never achieved such a sustained bombardment and the V-3 guns aimed at London were destroyed by Allied bombers before they could even be fired. A second set of two V-3 guns managed to shell Luxembourg during the Battle of the Bulge, but failed to do any significant damage and amply demonstrated why the original plan never would've worked even without the Allied bombers destroying the guns. Over five and a half weeks, they managed only 183 rounds fired (a far cry from the intended rate of fire) and only 44 of them were confirmed to actually hit the city, killing only 10 people and injuring 35. In addition to the inherent technical problems with the design, the Luxembourg bombardment was impaired by severe ammunition shortages due to the German railways being under constant air attack. This resulted in the gun crews improvising a much smaller 95kg sabot round containing only 9kg of explosives.
* The Karl Device. [[http://en.wikipedia.org/wiki/Karl-Ger%C3%A4t Have a look]]. The second largest calibre weapon ever fired in war, one shell weighed two tons, and each launching platform weighed 124 tonnes. Could only be effectively moved by rail, and was almost useless as tactical weapon. But ''two tons'' of explosives.
** Here is what it looked like when it hit the [[http://en.wikipedia.org/wiki/File:Warsaw_Uprising_-_Prudential_Hit_-_frame_2a.jpg old offices of the Prudential Insurance Company]] in Warsaw. Here is a picture of a [[http://en.wikipedia.org/wiki/File:Warsaw_Uprising_by_Joachimczyk_-_Dud_in_Adria_-_459.jpg dud]] shell. One was also used during the Siege of Brest Fortress, where the shockwaves from the impact could travel through metres of concrete and still be lethal.
* One of the weapons the Ottomans brought with them during their siege (and eventual conquest) of Constantinople was Basilica, a 27-foot long cannon that could launch cannonballs as heavy as 600 pounds up to a mile away. It probably didn't see much action due to a lack of effective ammo to get the desired results and required 60 oxen to drag it from place to place. It also took three hours on average to reload, giving the Byzantines a chance to repair the damage between each shot.
* The [=XM29=] OICW. It was a standard 5.56mm assault rifle with a 20mm grenade launcher that had programmable airburst grenades. Issues came about due to weight, cost, and the ineffectiveness of both the 20mm grenade and the rifle itself compared to the [=M16A2=][[note]]A nine-inch barrel went a long way to making the weapon ineffective versus the [=M16A2=] - for comparison, even the shortest M16 derivatives have never gone below a ten-inch barrel, and that's not including the five-inch flash hiders usually attached to them[[/note]]. The grenade launcher part did manage to spawn the [=XM25=], using a 25mm grenade, which has seen continued testing and actual service.
** The South Koreans actually managed to salvage the design in the form of the Daewoo K11, a combination of a 5.56mm assault rifle and a 20mm bolt action grenade launcher, with such features as a ballistic computer, thermal viewing capabilities and an effective engagement range of 300 meters, all while weighing 6.2 kilograms while unloaded. It was apparently tested in Afghanistan and while initially showing some serious defects (most notable defects with the striking mechanism and the barrel moving during firing) DAPA managed to repair these and the weapon is now fully functional. It has actually been successful enough to get export requests from several other countries, most notably the UAE and Saudi Arabia. Not so impractical after all. But South Korea makes no pretense that the K11 is suitable for replacing standard infantry rifles, as as the US tried to do with the OICW program; it's a specialist's weapon, issued to a couple of grenadiers per squad. What's impractical in one role can be quite practical in a smaller one.
* Arguably, a lot of the weapons in the US's Advanced Combat Rifle program could fall into this by the sound of it. Varieties include stuffing two bullets in a single cartridge[[note]]For example, the Metal Storm system, which used multiple barrels, each loaded with multiple rounds, to produce a storm of metal. However, the personal version of the weapon was ludicrously heavy (and the "artillery" version had serious design flaws), reloading was time-consuming, and accuracy was not a priority in the design, ultimately scrapping it[[/note]], making cartridges shorter by packing the gunpowder on the side, flechette rifles[[note]]While flechette cartridges are available for shotguns, the fin-stabilized flechette design (think of it as the fletching on an arrow) was designed to increase range and didn't do a very good job of it. In addition, the fins would frequently break or fail to deploy when the round was fired, making the bullet a lighter, ''more'' inaccurate round that frequently failed to reach the ranges they would supposed to, or even the ranges of standard slugs[[/note]], and caseless ammunition weapons[[note]]Caseless ammunition was designed to increase fire rate, by removing the mechanical necessity of ejecting a spent cartridge from the weapon after the slug was fired. While it worked, one thing the designers neglected to consider was that the ejected case also took with it a lot of the heat from the explosion of gunpowder. As a result, the barrels of caseless weapons would quickly overheat and warp from a ''single'' clip of ammunition, rendering the weapon useless[[/note]]. Unfortunately, none of these weapons produced results that were significantly better than what was available at the time. It didn't help that this program was obsessed with smaller ammunition that didn't perform any better all for the sake of MoreDakka (though many rounds, such as the 4.7mm round, were also designed with armor penetration in mind, and the thinking was that even if the bullets were individually less lethal the sheer number would make up for that).
* The XM-214 Microgun. Intended to be a man-portable version of the M-134 Minigun, it was scrapped when someone figured out two simple facts: 1) the combined weight of the gun, battery and ammo pack were still too much for any soldier to carry, and 2) such a huge amount of firepower is rarely actually needed - normal machine guns provide more than enough for the vast majority of purposes.
* [[DeadlyGas Chemical gases]] have been so effective at killing (in very gruesome ways) during UsefulNotes/WW1 that they had been banned from warfare. However, the only thing keeping the cloud of deadly gas over the enemy was the wind, which could and often did start blowing it [[HoistByHisOwnPetard towards the user's own lines]].
** Weaponized germs and viruses have a similar problem if used, except on an even greater scale. Any disease that had a high enough fatality rate and is transmittable enough to spread to many people quickly would also spread to the home nation of who ever used it.
* In the great Soviet tradition of '''moar''' firepower, the Soviet army designed their rotary cannons (the [[http://en.wikipedia.org/wiki/Gryazev-Shipunov_GSh-6-23 GSh-6-23]] and [[http://en.wikipedia.org/wiki/Gryazev-Shipunov_GSh-6-30 GSh-6-30]]) differently than the US: instead of being powered by electric motors they ran on the gas they themselves generated, which made them very fast to spool up and ''ridiculously'' [[MoreDakka dakka-capable]]. It did, however, come with a few slight issues: because they were adapted from the naval CIWS guns, the massive recoil and vibration, while quite acceptable for the much more massive ship installations, were putting so much stress on airframes that stress fractures and breakage of minor systems was practically a given (they had to install powerful lights near the landing strips, because the aircraft's own landing lights would almost invariably break upon firing of the gun), and not-so-minor ones like ''the landing gear'' would sometimes break as well. Oh, and a full magazine would be exhausted in less than two seconds of fire. And shells would occasionally rupture prematurely and damage the firing aircraft. And the cannon could be fired no more than ten times, because it was ignited by pyrotechnic charges. As a result, the final generation of Soviet fighters (and the post-Soviet Russian designs to date) have reverted to a single-barrel cannon (and repurposing the pyrotechnic charges of their rotary cannon to give the [[http://en.wikipedia.org/wiki/Gryazev-Shipunov_GSh-301 GSh-301]] the unique ability to unjam itself in the event of a dud round).
* In general, automatic combat shotguns. Weapons like the H&K CAWS, USAS-12 and the AA-12 are typically designed for close-quarters engagements in built-up urban or thick jungle/forest areas. However, where they have raw firepower, they lack versatility. With the military, shotguns are largely relegated to the role of door breaching and lack the versatility to quickly adapt from a close-range to medium-range threat like a rifle or carbine (the CAWS program was actually brought to a screeching halt simply because someone wondered what a soldier was supposed to do if they encountered an enemy further away than the 100-meter maximum range intended for the weapon). For the police, that much firepower is simply overkill and private citizens who want to own one have to go through a mountain of expensive paperwork.
** The [=Mk3=] Jackhammer never even got as far as most of the others (which are available for purchase): designed as one of the very first automatic shotguns, the Jackhammer was weighty, inaccurate (which is saying something when you're talking about a ''shotgun''), and most damning of all, could not be reloaded by hand. The only "clips" available were cylindrical revolver-like cartridges of 12 rounds which were only available, plastic-wrapped, from the factory. After the rounds were fired, the spent shells could not be removed and new ones put in: you had to sent it back to the factory for reloading. The weapon was very quickly scrapped, and only a dozen or so prototype versions were ever made, maybe two of which were actually capable of full-auto fire. But that being said, the Jackhammer had a devastating rate of fire and a surprising range when it ''did'' work.
*** True to this page's name, however, the Pancor Jackhammer's drum magazines could be placed on the ground and used as an Anti-Personnel mine. Slightly makes up for the fact that you can't reload the drums yourself.
* The M16, when first used in Vietnam, was supposed to represent the pinnacle of the modern assault rifle. It was made of lightweight polymers which reduced the rifle's weight tremendously while still giving the user the option of automatic or single shot fire, decent penetration for its weight, and a number of other features. However, mostly as a result of InterserviceRivalry and ExecutiveMeddling from Pentagon staffers who thought they knew a lot more than they really did, it was prone to clogging, corrosion and jamming in the jungle environment of Southeast Asia, mostly because the wrong type of ammunition was used, and because of its light weight, often felt like a toy to soldiers who were forced to use it (at least among Americans; South Vietnamese soldiers instead found the thing too heavy). It's since been in continuous service now for almost 50 years all over the world, and the basic concepts (lighter round, polymers, selective-fire) have all become standard for modern rifles. Regardless, the entire AR family still has numerous issues, so all the upgrades have taken it from just plain shit to regular bad.
** The immediate predecessor and the rifle the M16 replaced, the M14 was also an example of this. The M14 was a far more traditional rifle than the M16, with a body made of wood, mechanisms based on the M1 Garand rifle and firing a full-sized rifle round (the NATO-standard 7.62x51mm round). Unlike the Garand, it was selective-fire and could fire on full auto as well as semi-auto. The idea of the rifle was to replace several semi- and fully automatic weapons systems with a single do-all weapon that could reliably engage a target at any possible range. The fact that it was a more "traditional" rifle compared to the M16 also meant it was more widely accepted by the old guard of the U.S Military. However, it proved to be very flawed as a general infantry weapon. For starters, the M14 is two pounds heavier than an M16. Its ammunition was also heavier than an M16's, with the same amount of ammo becoming a much greater burden for a soldier trudging through Southeast Asia. The heavier round also resulted in heavier recoil, which made the M14 extremely inaccurate in sustained automatic fire. Finally, [[JackOfAllTrades in attempting to be a do-all weapon system]], it had [[MasterOfNone failed to surpass any of them]]. It was too light to be a squad automatic weapon, too heavy to be comparable to a submachine gun and one Department of Defense report went so far as to call it "completely inferior" to the M1 Garand. Most damning, the Springfield Armory could not produce it in the numbers needed for mass adoption (breaking a promise that had effectively sold the weapon over the FN FAL and thus gave the Pentagon the excuse it needed to not buy a foreign rifle; units in Vietnam were still equipping the M1 at the time of the M14's replacement). Eventually, the M14 was completely replaced as a frontline general-issue infantry weapon. It was however later modified into the M21 Designated Marksman's Rifle, a role it proved to be very capable in.
* In general, [[MoreDakka drum magazines]] tend to be this when compared to either traditional rifle magazines or a belt feed system. While they hold more rounds than a standard rifle or submachine gun magazine, and load faster than a belt feed system, they are also heavier than the former and a lot more finicky than the later. Because of the weight, a soldier could only potentially carry one or two. They can be reloaded by hand, but as you can imagine, reloading a 50, 70 or 100 round drum magazine by hand takes a pretty long time. Finally, they have a tendency to jam. That's why almost every firearm originally made with a drum magazine either had a traditional magazine made for it later or a belt feed system and why the G.I. issue version of the Thompson submachine gun cannot load drum magazines at all.
* The [[http://en.wikipedia.org/wiki/Urumi Urumi]] is an extremely flexible Indian sword, more like a whip that has a sharp edge to it. In the hands of a master, almost no one can get near the user and no parry would be able to successfully block it. In the hands of ''anyone'' else, they are as likely to slice their own leg off as kill the enemy. Another downside is that it requires a lot of stamina as swinging it around, even with two hands, is very tiring. There is a reason it considered one of the most difficult weapons in the world to master.

[[/folder]]

[[folder:Experimental Weapons]]
* The book [[http://www.amazon.com/My-Tank-Fight-Zack-Parsons/dp/0806527587/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1205083504&sr=8-1 My Tank is Fight!]] is all about impractical inventions of UsefulNotes/WorldWarII.
* AdolfHitler ''loved'' this trope. Here are just a few of the awesome and extremely impractical weapons that never quite made it:
** If the Tiger and Panther could have been considered Awesome but Impractical, what can one say about the enormous [[http://en.wikipedia.org/wiki/Panzer_VIII_Maus Panzerkampfwagen VIII Maus]]?
** The [[http://en.wikipedia.org/wiki/Landkreuzer_P._1000_Ratte Landkreuzer P.1000 Ratte]] would have been even more awesome and impractical. Dwarfing even the enormous Maus in size, not only would bridge crossings have been completely impossible for the 1000 ton vehicle, it would have destroyed any road it attempted to travel on! This tank would have carried a naval gun as its main armament.
** The [[http://en.wikipedia.org/wiki/Landkreuzer_P._1500_Monster Landkreuzer P.1500 Monster]] took the concept from impractical to nearly-certifiable insanity. This ''1500 ton'' aptly-named Monster would have a crew of over 100 and use the Dora Gun as its main armament! While it's true that nothing on land could have stopped it, it would also be an almost unmissable target for Allied aircraft.
** The [[http://en.wikipedia.org/wiki/Messerschmitt_Me_163 Me-163 Komet]], a rocket-powered airplane that had a seven minute flight time, flew too fast to effectively target bombers (its intended target), used two highly-corrosive fuels that spontaneously combusted upon mixing, desired or not. They also had a habit of spontaneously ''exploding'' if jarred too much by, say, a rough landing, and the thing flew so high that pilots were required to eat a special diet in order to reduce intestinal gas. No pilot ever scored more than one victory with it. It was also made of wood to keep the weight and costs down, and while it had wheels when it was going up, they broke away from the aircraft as it took off. What did you land with? ''A single skid''. The best part was that at this stage of the war, even flat runways were in short supply, so the pilots had to land them in bumpy, rocky fields. And since they turned into gliders to boot, they were completely defenseless from enemy fire. More pilots died trying to land these things than in combat. Oh, and the engines were considered more valuable than the pilots. What does ''that'' tell you?
*** The whole idea was so poorly worked out that there were multiple incidents of these aircraft destroying themselves on takeoff '''with their own launch wheels'''. Because of the poor fields they were taking off from, it was entirely possible for the rubber-tired take-off wheel assembly to bounce higher than the altitude it was dropped from...and smash into the plane, often resulting in a catastrophic explosion.
** The [[http://en.wikipedia.org/wiki/Bachem Natter]] (unrelated to Administrivia/{{Natter}}), a vertically launched rocket-engined interceptor that carried its offensive armament of rockets directly in front of the pilot. Endurance was even shorter than the Komet, but missions ended with the aircraft breaking apart and the pilot being thrown free. So impractical it was never used operationally - and the only manned test killed the test pilot.
*** Because it wasn't already insane enough, the original project (later scrapped) had the pilot expend his rockets on the enemy aircraft, then steer the Natter on a collision course with one of the surviving bombers and only ''then'' eject. With any luck.
** [[http://en.wikipedia.org/wiki/Blohm_%26_Voss_BV_40 Blohm & Voss BV 40]] Glider fighter - sort of a one shot deal, proposed to spare fuel/strategic materials for resource-strapped Germany late in the war.
** The [[http://en.wikipedia.org/wiki/Silbervogel Silbervogel]] bomber, a semi-orbital intercontinental bomber. Too impractical to build at the time, and would have had a disappointing payload in any case and would have burned up on atmospheric reentry after its flight. The inventor figured out that the thing would never be able to work half way through designing it, but continued to work on it anyway for the insane amount of money the Nazis were giving him.
** The ''ne plus ultra'' of impractical Nazi inventions was the [[http://www.damninteresting.com/the-third-reichs-diabolical-orbiting-superweapon Sun Gun]], an orbiting mirrored space station intended to be a solar KillSat. Oddly enough, also counts as MundaneUtility: in addition to establish Nazi superiority, the designers recognized its usefulness as weather satellite and communications platform.
* [[http://en.wikipedia.org/wiki/Northrop_XP-79 The Northrop XP-79]] was intended to be a rocket-powered flying wing fighter that would destroy incoming bombers be '''[[RammingAlwaysWorks ramming them]]'''. (No, they thought of that, it was designed to take the impact without significant damage.) Three prototypes were built, two were abandoned after the rocket engine failed to perform adequately, and the project was entirely cancelled when the remaining prototype, fitted with conventional jet engines, was lost (and the pilot killed) after an unexplained loss of control during test maneuvering.
* The Soviet Union/Russia, like the Nazis mentioned above, came up with some impractical gems for battle. In fact, it sometimes seems that the only reason they would design and build these weapons was just to prove that ''they could'':
** Cast in 1586, [[http://en.wikipedia.org/wiki/Tsar_Cannon the Tsar Pushka/Tsar Cannon]] is recognized as the largest cannon by calibre, with a barrel nearly ''18ft'' in length and a bore of nearly three feet. However, it wasn't actually designed as a bombard (the mount and shot displayed nearby are decoration made in 1835): its intended purpose was to be the largest shotgun ever made. Mounted on a fortress wall, it was to be loaded with 1,600 pounds of grapeshot and used against attackers. But by the time it was finally completed, the Tatar threat to Moscow greatly diminished and it never had a chance to be used in a battle. Still made a neat showpiece, though. In fact, showing off the prowess Russian bronzeworkers was a major purpose from the start.
*** During restoration in 2008, gunpowder residue was discovered, meaning it was fired at least once.
** [[http://en.wikipedia.org/wiki/Antonov_A-40 The Antonov A-40 "Krylya Tanka"]] is... a ''Flying. Tank.'' It's [[NinjaPirateZombieRobot a tank with wings]]. If anyone remembers making paper airplanes as a child, you can understand where the problem comes in. Tanks weren't/aren't designed to fly for good reason: [[CaptainObvious they're heavy]] and aerodynamically unsound. To actually make it possible for it to fly this stinkin' thing, it was stripped of most of its '' ammunition, armament, armor'', and [[ArsonMurderandJaywalking headlights]]. This made it less a tank and more of a very heavy and cumbersome armored car that would have had very limited survival once on the ground, let alone still in the air. Only one was made, and in its solitary test, it did in fact fly... but was still far too heavy and overtaxed the tow-plane's engines to the point it risked a fire. The project, not surprisingly, was scrapped afterwards.
* The Western Allies got in on this to. Due to the German blockades, the British had a huge shortage of steel during the early part of the war, which was needed to create new carriers and the like. One genius came up with an idea: "Pykrete", a mixture of ice and wood pulp, such as sawdust or even old newspaper, that creates a material stronger than pure ice that still floats, but is also resistant to melting. Then, make a huge unsinkable ''aircraft carrier'' out of the stuff. It never got past a theoretical stage, because the giant refrigeration units that would be needed to produce ice on a scale to build a capital ship would consume just as much steel as one built the conventional way.
* The [[http://www.merkle.com/pluto/pluto.html [=SLAM=]]]. Imagine a locomotive. Now, imagine that locomotive with a ''nuclear'' ramjet engine, flying at three times the speed of sound at low level, lobbing nuclear bombs at things. Even without the nuclear bombs, the shockwave, exhaust, unshielded reactor, and fission fragments would destroy, kill and irradiate whatever it flew over. Unfortunately, the problem with building a weapon that spews nuclear waste everywhere is that nobody will give you permission to ''test-fly'' the damn thing, and your allies might disapprove of it flying over their countries to get to the USSR. Finally, nuclear tipped [=ICBMs=] are a lot cheaper, and get to their targets faster.
** The design also called for the drive reactor to be the primary warhead. This forced compromises in design that made it neither very good as a reactor nor very good as a bomb.
* [[http://en.wikipedia.org/wiki/Convair_X-6 The Convair X-6]], a ''nuclear powered'' bomber. The X-6 had potential if it was practical, such as being able to stay aloft in the air for ''weeks'' at a time without refueling. But to shield the crew at a minimal safety level required ''12 tons'' of lead and rubber. While test flights with an operational nuclear reactor on board were conducted on a similar aircraft as a testbed, the X-6 never got off the drawing board.
* The Soviets had their own nuclear powered bomber, the [[http://en.wikipedia.org/wiki/Tupolev_Tu-95LAL Tu-95LAL]], which did partly solve the weight problem of the Corvair X-6 by mainly shielding ''the crew'' instead of the reactor itself[[note]]while the reactor did have the shield, it was relatively light, and mainly served to protect the mechanics working on the plane from the inactive reactor, with full shielding only in the cockpit direction[[/note]], but while it was more practical (it even flew a couple of times with the reactor on), it still was too large, unwieldy and expensive, not to mention hugely dangerous in a crash. When the first practical [=ICBMs=] arrived the project was canceled.
* The [[http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion Nuclear pulse propulsion rocket]] concept made even the SLAM and Corvair X-6 look sedate and practical by comparison. This design used the periodic ''detonation of nuclear bombs'' for launch and forward propulsion. Surprisingly, it might have been quite [[OrionDrive practical for space travel]] from an engineering perspective, but it was hideously impractical politically (the nuclear detonations would violate the Partial Test Ban treaty, and that's before even considering public opinion).
* The Chinese failed epically with the [[http://en.wikipedia.org/wiki/Chengdu_J-20 J-20]]. Why? It's only stealthy from the front, basically meaning it's a missile, with a person in it. [[SuicideAttack Gee, I wonder what that means?]]
** If nothing else, it means that it's at least hard to detect by its target once it's laying in an attack run. Getting ''away'' from the target if they didn't neutralize the defenses in their strike could cause them some grief, but that's true of most attack planes.
* So far, [[http://en.wikipedia.org/wiki/Railgun Railguns]] are much more Awesome than they are Practical. Despite current tests showing that a Railgun can fire a 3.2 kilogram/7 pound projectile at Mach 7 speeds, there are still crippling issues with powering the gun as well as the heat from firing wearing it out quickly, limiting how useful it would be as an actual weapon. However the project cost for developing the Railgun is a lot lower compared to some of the other examples on this page (along with the finished version expected to a little more damage than a Tomahawk missile at a fraction of the cost), which has seen it survive several rounds of budget cuts.
** More feasible than railguns are '''coil'''guns. Some already exist, as seen [[http://en.wikipedia.org/wiki/Coilgun here]]. Coilguns circumvent the projectile-on-barrel friction that is the cause of a railgun's severe firing wear, by hurling a '''[=MagLev=]''' bullet.
* Not really a ''weapon'' per-se, but in UsefulNotes/WW2, the British experimented with a "Parachute-less Air Drop". Basically, the idea was to use small rocket thrusters to negate the speed at which a supply crate fell from the air, allowing it to safely lower to the ground. Unfortunately, the rockets were very finicky. In tests, they would either activate too soon and thus spend their fuel before they hit the ground, or slam into the ground at near-terminal velocity ''then'' fly up into the air, flinging whatever was inside and large spintered timbers about the landing zone. This idea was so impractical, it never got past the 'drop twenty feet from a crane' stage.
** There was a reason for this: very poor supply of silk in Britain to make parachutes. Other fibers are either too heavy, or too weak, and the three major producers of silk were China, Japan and Northern Italy, all in Axis hands till 1945. Only the development of Nylon in late 1944 allowed a large (millions-strong) number of parachutes to be made for the D-Day airborne ops.
** Other nations continued the development, though, and similar technology (in addition to conventional chutes, mind you) was introduced by Soviet Union to cushion the final landing impact of heavy airdropped loads, such as [[AwesomePersonnelCarrier APCs]] and supply containers. Both USSR/Russia and US used it as a last-second landing engines for their space capsules/ interplanetary probes, and as recently as August 2012 US used a pure rocket-engined sky crane to land its latest Mars rover. The newest Russian capsule is also planned to eschew parachutes and land on aerobraking and rockets only, and Elon Musk has declared that if [=SpaceX=]'s Dragon capsules cannot make a soft landing on Earth using only rockets and aerobraking, the project will have been a failure in his eyes.
* Project Babylon was Iraq's attempt to build a supergun that would have rivaled the Nazis' V-3 project. The project would have called for the construction of 2 1000mm cannons and a 350mm prototype, each 156 meters long. The full size cannons would have been capable of firing conventional shells over 1000 kilometers, or firing rocket assisted shells straight ''into orbit''. The guns' intended uses were to either deliver nuclear, biological, or chemical tipped warheads or to disable enemy satellites. However, like the V-3, the Babylon guns suffered from the drawback of being locked into facing a single direction, as well as being gigantic and impossible to hide. The gun was so impractical the Israelis never considered it a serious threat. The project ground to a halt after its lead designer was assassinated (whether by Israel or Iran remains uncertain; both were more concerned with his simultaneous work on improving the accuracy of Iraq's ballistic missiles), and the guns were dismantled and destroyed by the UN after the First Iraq War.
* The [[http://en.wikipedia.org/wiki/Boeing_YAL-1 Boeing YAL-1 Airborne Laser]]. Essentially a Boeing 747 with a WaveMotionGun, designed to shoot down [=ICBMs=] with a laser beam during the missile's launch stage. Unfortunately the laser itself proved too expensive and required too much power, plus the massive aircraft would be a sitting duck against enemy fighters (problematic since the laser would need a line of sight to the [=ICBM=] immediately after launch, requiring flight very close to launch site), and the project was cancelled.
* The [[http://en.wikipedia.org/wiki/Panjandrum Panjandrum]] was one of the few Allied experimental weapons in WWII that was too crazy to work. It was basically a giant, rocket propelled wheel designed to carry a large load of explosives directly into beach fortifications. Unfortunately, the thing was literally impossible to control, and had the nasty habit of veering off course and going into unpredictable directions. Not to mention the fact that the rockets would sometimes separate from the wheel, firing off in random directions as well. Suffice to say, the project was scrapped after one demonstration in front of a panel of high ranking officers went horrible awry when the panjandrum veered off course and nearly collided with the gathered spectators.
* The Mark 90 Nuclear Bomb (aka 'Betty') used as a depth charge...let me repeat...a NUCLEAR DEPTH CHARGE!!!! It was released in 1955 and removed from service in 1960. The Betty had a 5 kiloton warhead. Just for reference, the Hiroshima bomb had a 15 kiloton warhead...boggles the mind. Awesome, but irridating dolphins and whales and just about everything in the ocean was probably not a good idea.
* The TOG II, a British interwar tank design that was based around the idea that WWII would be just like WWI; thus, the TOG was to be a "breakthrough tank". Slow, lumbering, but heavily armed and armored, designed to dismantle enemy trenchlines and allow smaller tanks to pour into the gap and exploit the hole the [=TOGs=] had made. It was ''33 feet long'' and weighed eighty tonnes; despite this, it reportedly trialled successfully, reporting no reliability or mechanical issues. Sadly, WWII was not like WWI, and this feat of engineering - though not common sense - was not put into mass-production and never saw action.
* Towards the end of the second world war war, the Allied planners had to find ways of breaching the German Siegfried line of defenses on the River Rhine. One school of thought held that very heavy armored vehicles - purpose built for the task - would be sufficient to knock a large enough hole in the German defenses that the Allies could then exploit with faster armor. Both the United States and Britain designed and built ''vast'' super-heavy tanks designed for the sole purpose of breaching the lines:
** The US offering was the T28 Super-Heavy Tank, sometimes known as the 105mm Gun Motor Carriage T95. Weighing in at 95 tons, 36 feet long, with a 105mm main gun and ''300 mm'' of frontal armor, this lumbering monster had a top speed of only 8 miles per hour on roads[[note]]Some witty ''VideoGame/WorldOfTanks'' players have suggested that it didn't move, it just turned the planet beneath it.[[/note]] and an engine that had less power than some modern production cars, which meant it was barely able to climb hills. It was also too heavy to use most bridges, too low and slow to ford rivers, and too wide to haul by rail. Its gun elevation and depression was also lousy. One of the two prototypes was destroyed by a fire, whilst the other sat in a Virginian field for 27 years before a hunter found it and decided to tell someone. It is now on display in Fort Benning, Georgia.
** The British came up with the Tortoise, which was (''slightly'') more practical than its American cousin. Weighing 87 tons, and 33 feet long, a single Tortoise actually made it to Germany, but far too late to see action. Slight less well armed and armored than its American counterpart with a 94mm gun and 228mm of frontal armor, it was however designed as though it might actually, y'know, drive somewhere, with a more powerful engine that enabled it to blat along at a sprightly 12mph. In trials it was found to be a decent gun platform and also fairly reliable...unfortunately, the military need for it had completely dried up. Still, Tortoise actually got into the production stage. For a total run of six vehicles. One - in ''running condition'' - is displayed in Bovington Tank Museum, whilst another is used as a target at Kirkcudbright Military Training Area.
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