As shown below, just about anything can be used as a weapon.
The most famous swordmaster in all of history, Miyamoto Musashi, occasionally chose to fight with a bokken (wooden sword), and consistently won with them. In his fight with Sasaki Kojiro (his most famous fight), he wielded a bokken carved from the oar he used to row himself there.
And he in turn allegedly lost only once - to an elderly monk wielding a hoe.
Supposedly at some point the famed swordsman came to eschew steel swords in favor of wooden ones after becomed sicked by the number of promising swordsmen he killed in duels, and no matter whether he used a steel or wooden sword, still only suffered the one defeat.
According to one legend, Musashi's sole defeat was at the hands of Muso Gonnosuke, the founder of Shinto Muso Ryu. One version of the story goes that, Muso, using a bo, dueled Musashi, and was defeated when the sword master broke his staff. Distraught, Muso carried the broken staff with him and meditated until he recieved a divine inspiration on how to use it to overcome Musashi's two sword technique. They dueled again, this time with Muso as the victor. The shorter stick, the jo, was preserved in Muso's system. If true, this is an oddly recursive case of a seemingly-useless broken weapon being used as an improvised weapon. It was also, of course, just a stick: one of the original improvised weapons in Real Life.
Most of the weapons traditionally associated with ninja started out as farming implements and underwent little transformation. The reasons for this were twofold: firstly, because ninja were not members of the samurai class and so did not have the legal right to own proper weapons; and secondly, because real ninja were not the highly visible sort and carrying something that could do legitimate work was a lot less conspicuous. Examples include the kunai (originally a trowel), shuriken (the most common form, the bo shuriken, is basically a stake), sai (prying tool), and kusarigama (lawnmower).
Perhaps one of the most infamous and iconic improvised weapons in the real world is the Molotov Cocktail, a weapon which has such ordinary components as gasoline / petrol, a glass bottle, and some sort of wick or fuse (often a cloth rag). It was successfully used by the Finnish against intruding Russians.
The original recipe was a cocktail, in that components were mixed and shaken up, particularly, a small amount of tar was added to the gasoline to make it stick to the target. Leslie Thomas gives the full recipe in one of his stories where a Spanish Civil War veteran is teaching British Home Guards in World War II how to make them and disable tanks with them.
In fact, it was so effective that it was later mass-produced specifically for tank-killing purposes.
There's a story about King George VI being given a demonstration of the new weapon. When asked if he would like to try one, he is reputed to have said "Save them for the Germans."
One of the other methods of disabling tanks in the absence of a proper anti-tank weapon was to simply cram a log in the tread assembly, which caused the tank to throw a tread and become immobilized.
Another World War II improvised antitank weapon was the "sticky bomb", a sock filled with TNT, rigged with a simple fuse, and dipped in Kerosene to make it sticky. Soldiers would run up alongside an enemy tank, attach the bomb to the tread, light the fuse, then run like hell.
The sticky bomb wasn't a very effective "improvised" anti-tank weapon. Although it was made with simple materials, the British soon issued sticky bombs to their troops, with adhesive to make it stick better. It was ineffective because it had a tendency of going off prematurely or sticking to the user when lighted.
Prime example was in Saving Private Ryan: in this case, it falls in line with holding a grenade for too long...
Pipe bombs. As their name suggests, made from a short length of metal or PVC pipe packed with explosive material. The Unabomber was famous for making ones with nails. One person killed himself with a pipe bomb stuffed with shredded playing cards.
Shivs, MacGyver-like knives typically made by prison inmates out of ordinary things such as sharpened toothbrushes, spoons, styrofoam, pieces of paper, and chicken bones.
Prisoners occasionally show remarkable ingenuity when it comes to designing makeshift weapons. An episode of MythBusters successfully demonstrated the potential of a crossbow made from rolled newspaper and an elastic waistband.
Prisoners have been known to shit and piss into a bucket and keep it in their cell for days or more, allowing it to fester and become truly disgusting. Just so they can throw it at the guards.
The Pen Gun, a testament to Norwegian ingenuity, is made from standard office supplies and can launch a pencil through a soda can. More than enough to penetrate the tranchea or temple.
Roman senator Tiberius Gracchus was killed with a bench. A little later, the tribune Saturninus and his followers were murdered while being held in the Senate house—some impetuous aristocrats climbed onto the roof and threw clay roof tiles down on them.
In WWI, soldiers in the trenches would sharpen their entrenchment tools (small shovels) and use them in hand-to-hand combat.
An American knife company makes a reproduction of the Soviet MPL-50 entrenching tool, with particular emphasis on the fighting and generally offensive applications of it.
The British Army has achieved respectable results when called upon to perform crowd-control duty by issuing its soldiers with pickaxe handles. The practice apparently began when security was needed for the officer detailed to collect the garrison payroll from a bank, as rifles would tend to over-penetrate.
On Deadliest Warrior, the Green Berets were shown to use entrenchment tools. These were pre-sharpened, and they were trained in their effective use as weapons.
The French Army was one of the leaders in the development of trench knife designs and concepts. Besides shortening long sword-like bayonets and commissioning the development of new designs, unit blacksmiths fashioned field expedient weapons such as the French Nail, made from stolen barb wire stakes. Supposedly the Nail was so successful the Germans stole the design and concept after they encountered them firsthand.
The Millwall Brick, a testament to human ingenuity in coming up with a way to kill each other with newspapers snuck into football events.
Robert Rankin has a scene in one of his novels where an SAS veteran folds a newspaper into a dagger and uses it to stab a hole in a bar counter. This was probably based on the Millwall Brick.
More likely the Chelsea Brick popularized by W.E. Farbairn while he was training the S.O.E.
For more improvised weaponry, consider the first two sentences of the history article of that page:
"In the late 1960s — in response to football hooliganism at matches in England — police began confiscating any objects that could be used as weapons. These items included steel combs, pens, beermats, Horse Brasses, Polo mints, shoelaces and boots."
'Chechnyan Firecrackers'- otherwise known as home-made guns. If you have something explosive, materials and tools to work with and maybe even bits of actual guns, with the right know-how any enterprising rebel, terrorist, gang member or ordinary person can build a usable firearm of some sort, though safety is not a guarantee. As the nickname suggested, Chechnyan rebels are well-known for creating and using guides to build these. The Other Wiki has an article about this.
Britain's heavy restrictions on firearms (handguns are illegal and the police make spot-checks to ensure owners haven't got careless about storing their weapons under lock and key) severely limit the black market supply of proper firearms, so the next best thing for your average would-be armed robber are crude derringers kludged together from starting pistols and replicas. Firing one is either an act of great courage, great foolhardiness or both.
Leon Trotsky was eliminated with the use of an ice ax.
On another occasion, Indian soldier Yogender Singh Yadav used his ice axe to hack down opponents in an assault on a enemy position during one of the Kashmir wars.
Do not try this at home (even though you will anyway, fun disclaimer): There's a YouTube video floating around of a person who filled a Super-Soaker tank with WD-40, attached a flaming rag in front of the nozzle, and made a pretty effective flamethrower.
Somewhere around 2003, a kid built a functional flamethrower out of PVC pipe (for the tank), hose, copper tube (handle), a gas line tap (valve), able to shoot a 12 yard jet of flame, and a lot of people immitated the design. Subversion: it still needs a (relatively high-tech) tire inflating compressor to load and pressurize it before it fires.
Inverted by a guy who built what he planned as flamethrower and decided to test it with water. The performance was seriously impressive and he went on to use it to for water fights.
Low-quality softair guns powered by a small gas tank are known for discharging their tank in a few shots if fired upside-down; instead of the small puff of gas that is normally used to propel the pellet, they dump a third or so of the tank, emitting a jet of ice-cold gas. The nozzle for refilling the gas tank has the same size as the one for refilling butane lighters.
The term "platik" in the Philippines refers to both improvised firearms created in back-alley workshops and homemade guns. According to The Other Wiki, the term originated late in the Philippine-American War when guns and ammunition had become scarce. The most common form of the weapon was a gas pipe attached to a rifle stock. Wire was usually wrapped around the barrel to keep the pipe from expanding when the gun is fired. It was muzzle-loaded and fired a medium sized bullet or musket ball. A small hole at the breach end of the barrel accommodated a cigarette or match that was used to ignite the primer, making aiming difficult. This also gave rise to the nickname, "Cigarette Gun". Modern paltik guns can range from crude constructs of pipe and metal to functional copies of real guns. The construction of such weapons was so common in the Danao city area that the government just decided to legalize the clandestine gun-makers rather than go through the headache of trying to clear out all of them.
Irregular Vietnamese forces in the Vietnam war used a vast array of homemade and converted weapons, some as simple as a length of pipe fitted with a crude breech and a rubber band and nail to act as the firing pin, firing shotgun cartridges. They would then set up a trap designed to ensnare or otherwise disable an enemy soldier, lie in wait near the trap, and once the trap is sprung they would just walk up to the poor guy and execute him, "liberating" him of his weapon. They'd then hand off the improvised weapon to the next poor guy who has to make do with it.
Home-made guns in the USA were called "zip guns" they were very unsafe, and as handguns have become more readily available they are mostly forgotten.
There was a CCTV recording showing a hotel clerk successfully fought off robbers with a fire extinguisher when they think they have everyone under control.
Technicals, which are usually nothing more than civillian pickup trucks with salvaged guns or rocket tubes welded on, have proven to be effective in combat in the Middle East and North Africa whenever proper fighting vehicles are hard to come by. What technicals lack in armor, they make up for with speed and maneuvability, and are much less costly to produce, allowing belligerents to deploy them in large numbers to compensate for their fragility. Although as some such forces have learned from time to time, even a large number of such technicals are no match for proper armored vehicles in a force-on-force battle. Most machine guns will do little more than get the attention of a tank, and many of the rocket launchers will lack the penetration required if fighting armored vehicles head-onnote For most armored combat vehicles, the bulk of the armor is on the front, with the assumption that they will most often be facing their enemy. There is less armor on the sides and back, and the weakest armor is typically on the top and bottom of the vehicle, which is why the most effective way to kill a tank is often to use an airplane or a helicopter with missiles..
Many of the classic weapons of martial arts were improvised, as their origins dated from a time when swords were forbidden to anyone outside the samurai class. The bo staff was a wooden pole used to carry buckets of water; the sai was a piece of metal that kept wagon carts attached to the wagons. Tonfa were handles taken from wells. Nunchaku were implements used to whip horses (or to thresh grains; history is a little unclear on this one). Kamas and sickles were for cutting crops or grass.
The self defence manual Street Ninja, by one Dirk Skinner (if that's his real name I'll eat my hat) uses the term TOYS for Tools Of Your Surroundings to mean a bunch of sand or coins slung in an assailant's face, a bottle snatched from a bar, a key between your knuckles etc.
On a side note, NEVER hold a key between your knuckles and try to hit someone. The key will twist and at best go down, and at worst, go up and slice into the webbing between your fingers. Hold the key between your thumb and index finger, much better for stabbing.
Israeli author Eugene Sokut recounts a tale where an old man uses keys between the fingers to open the face of a young troublemaker. The old man was a former commando with enough expertise that the keys were likely unnecessary as a weapon to begin with, though. Ultimately, the author used the tale to underscore the point that using keys between the fingers was not a favorable tactic for a novice.
When it comes to keys, your best bet is throwing them into the face of your opponent. Try it on soda cans, milk cartons, something similar and you'll see the kind of damage it does. Although, this troper has seen keys used in a fight not to stab, but held between the knuckles and raked across the opponents face like claws.
Tyre irons. The lever-type can be used as a cosh and the cross-type can be used as a giant shuriken (or vampire repellent), in addition to having hand-guards. It's also great to parry with, what with all the angles.
With knowledge in in human anatomy and physiology (particularly concerning arteries), any rigid pen or pencil can become a lethal weapon. It is for this reason that the pens issued in prisons are the bendable kind.
Probably half of the hand weapons in any book of medieval military technology first started out as this trope, when farmers who didn't own any decent weapons adapted their agricultural implements as pole arms, nunchaku, caltrops, etc.
Additionally, there's actually a significant difference between axes specifically designed for war, and the sort of axe a peasant farmer would have lying around his home. The latter has a deep, wedge-shaped edge ideally suited for cutting or splitting wood, and were not actually intended for use in warfare. While it certainly can be pressed into service as a functional weapon, a true military axe has a thin and almost sword-like edge, and is much better at cutting and hacking flesh. This makes the use of common wood axes a case of this trope, as well.
Even honest-to-goodness guns can be used this way, if circumstances arise that prevent you from using them for their designed purpose (out of ammo, weapon malfunction, bad guy inside the effective range, etc.). Members of the armed forces are trained to use their firearms as melee weapons, including a fluid set of four melee attacks for use with a rifle note These are called Buttstrokes (Stop giggling), You swing the butt of the rifle up, then thrust the butt forward, then swing the barrel down, slashing them with either the barrel or an attached bayonet. Then you can either try to hit them with the butt again, or jab them with the barrel (the last two moves make a lot more sense with a bayonet attached)
And bayonets are an example of turning a rifle into an improvised weapon, in this case, you make it into a short spear by sticking a knife on the end.
A bayonet isn't an improvisation if the gun is designed to mount them.
Or even on some guns NOT designed to mount them. The Plug Bayonet was rammed into the end of a musket after it was fired for charging into close quarters combat. It was quickly realized that it was rather better to have a bayonet that could be attached before firing the gun, since time is rather short in the middle of a battle, and bayonet lugs were invented.
In September of 2010, Sergeant Dipprasad Pun of the Royal Gurkha Rifles apparently beat a Taliban attacker off a rooftop with the tripod of a heavy machinegun. The thing weighs about sixteen pounds and is made of solid steel, so smacking somebody with it is probably a lot like whalloping them with a warhammer.
The Dutch were infamous throughout their history for using their own country as a weapon. Because most of the populous west lies below sea level, more than one war has been won by breaching the right dike at the right time and flooding or cutting off enemy troops. Once, they even sailed their own fleet inland to liberate a besieged city.
In a similar vein, the Russians have repeatedly used their merciless winters (promoted to General) against invaders. Both Napoleon's and Hitler's armies have been savaged by them. One of the few nations to use this successfully against Russian troops were the Finns during the Winter War, when they would (among other things) systematically destroy field kitchens of Red Army detachments. Having no hot food in -40C conditions is very bad for you.
Inverted by king Karl X Gustav of Sweden in 1658, when he used an unusually cold winter to march the entire Swedish army across the normally open sea and invade Denmark. (This had evidently been done before on a smaller scale; an old Danish law says that any Swede who walks across the ice to Denmark may be beaten with sticks.)
Older Than Dirt, unsurprisingly. The oldest unequivocal weapons known to archaeology are the Schöningen spears, approximately 400-375 millennia old. They were simply carved from wooden poles, and don't have any points hafted on them.
The 1933 "Battle of Stockton", a clash between fascist Blackshirts and pissed off locals, involved a great deal of improvised weaponry, ranging from sticks, pickaxe handles and stones, to at least one potato studded with razor blades. The latter actually managed to take one fascist's eye out.
ANFO, fertilizer and diesel, mix and voila, instant bomb. And you can make a gun with an door bolt for the firing mechanism and a bullet with a bamboo section full of match heads and a nail. Put it all in a pipe and ad a pebble in front of it, you got a gun now. Mac Guyver for all!
One of the hazards of being a teacher trying to break up a fight between students in schools (especially those with severe disciplinary problems) is the fact that sometimes said students use school supplies—pens, pencils, scissors, etc.—as weapons.
During his time as Prime Minister of Canada, Jean Chrétien once had an intruder get into 24 Sussex, the Official Residence of the Prime Minster, while he and his wife were home. He grabbed a smallish Inuit soapstone carving as an improvised weapon. Doesn't count as any sort of Badass, though. He was hiding in the next room while his wife was talking to the intruder, keeping him busy until the security detail was able to get inside and deal with the problem. This doesn't say much about the security detail being all that Badass either. (The time he broke away from his security escort, proceeded to wade through a crowd, and started to strangle some poor schmuck who didn't get out of the way fast enough doesn't say much about the quality of the security detail or his suitability as a person at large, either.)
The Browning Automatic Rifle was designed as a light machine gun for the US Army during World War One and was used heavily in World War II and The Korean War. It was not unknown for soldiers to cut off the bipod, which both reduced the weight and practically turned it into an assault rifle (which was what it pretty much was anyway).
It is a general rule that any weapon will be used for a mission it is not intended for once it is discovered it is useful for that. Examples are the German 88 which could fulfill both anti-aircraft and anti-tank, the bazooka which was found to be useful for destroying fortifications, and the B-52 which was originally for dropping nukes but turned out to be extremely useful in raining Death from Above on conventional troops.
Another good example: Self-Propelled Anti-Aircraft Guns. Most of these, such as the ZSU-23-4 have multiple rapid-firing machine cannons or rotary cannons. While initially designed to defeat helicopters and fixed-wing aircraft, they have proven themselves equally good at fighting infantry in mountains and urban areas. This is equal parts due to their higher rate of fire compared to conventional tanks and their higher range of elevation on their guns, meaning that they can rake even the tallest buildings or steepest cliffs with high-explosive cannon fire.
The M45 Quadmount during WWII is perhaps the first example of this. An electrically-powered turret mounting four M2 .50 machine guns, intended to be a highly-portable anti-aircraft weapon (easily mounted on the back of a truck), but it was quickly adapted to anti-infantry use and given the nickname "Krautmower". (Due, in part, to the fact that by the time it was deployed in combat there weren't very many German aircraft left for it to shoot at, but still lots of ground troops.)