"It's never a good idea to glorify war, but holy shit do fighter planes make it hard not to. It's not just the badassery of the machines themselves, but the fact that being a fighter pilot takes a special kind of balls that borders on crazy."
A Brief History Of Military Aviation
Almost as soon as the aircraft was invented, men decided it might make a nifty way of killing other men without getting too much blood or mud on one's uniform
. The history of military aviation is a story of rapid technological evolution closely coupled with human excellence and bravery (and extreme violence as well), and as a result has been an abundant source of material for almost every kind of narrative media. It has also had massive effect on the development of modern warfare. On every level of military planning the ability of military aircraft to support or interdict must be taken into account. In addition to their importance in regular action, aircraft have often been used in extraordinary actions
in which relatively small forces have acheived disproportionally great strategic advantages. This means that the outcome of warfare between roughly equal opponents in the early 21st century can be extremely unpredictable, in contrast to the situation in the beginning of the 20th century when stalemate was more or less the only possible outcome.
The fictional airman is often an Officer and a Gentleman
, and/or a Military Maverick
. Neither trope is completely without real life basis.
The first military branch to incorporate aircraft in their doctrine was the Navy: from 1911 to 1913 all major navies had fledgling air services using small floatplanes, medium-sized flying boats, and large airships. Their primary role was reconnaissance. While the sighting range from a ship was around 20 kilometers (11 nautical miles), an aircraft at 3000 ft had a sighting range of nearly 100 km (54 n.m.). In addition, aircraft were good for spotting minefields and submarines.
They soon picked up another role, the air strike
. Even the smaller aircraft could carry flechettes, light bombs, or rockets, which made them essentially self-spotting long range artillery. The first recorded bomb dropped from an aeroplane was during the Italo-Turkish war of 1911-1912, but naval aviation developed this role a lot during World War One
. Special carrier ships could deliver air strikes against land and sea targets, and torpedo-carrying aircraft and dive bombers were soon able to threaten even capital ships. Come World War II
, naval aviation quickly showed that air superiority was essential to naval operations, offensively and defensively.
Turning the airstrike Up to Eleven
, very soon several countries were building very large aircraft
carrying bomb loads of several hundred kilogrammes to strategically bomb targets in the enemy's homeland. Until World War II
, many military theorists believed that fleets of bomber aircraft were going to be the
decisive weapon in future wars (thanks to the development of interceptor aircraft and radar warning systems, these expectations weren't quite fulfilled). The most common type of bomber during WWII was the twin-engined medium bomber; only the British and Americans used heavy bombers.
The armies initially found little use for aircraft. The infantry still didn't move very fast and units were generally very easy to spot when moving, which made air reconnaissance less important to land warfare. Until the invention of the tank, infantry didn't really present any hard targets needing special attention either, except for bunkers which were invulnerable to early aircraft-carried weaponry. Aircraft were
useful for artillery spotting, but until radio equipment light enough to be carried by aircraft had been developed (around 1915), communications between ground and air were crude and tedious. As military aircraft became more efficient through use in other branches, they eventually became crucial to the army too. Ground attack planes could be used for supply interdiction, and could attack enemy formations, fortifications, and armored vehicles in coordination with army units — these activities were later developed into Close Air Support tactics.
In the inter-war era, transport aircraft gained sufficient capacity to allow deployment and supply of troops
, and airborne infantry units were set up in Italy, the Soviet Union, Germany, Japan, France, and Poland. During World War II
the assault on Crete by German paratroops was so impressive to the British and Americans that they created airborne infantry divisions of their own. Ironically, the heavy losses during the same operation caused Hitler to cancel further airborne operations by Germany.
Aircraft of course also attacked each other. At first air-to-air combat was sporadic, erratic and inefficient. The introduction of the machine-gun in aircraft ushered in the era of dogfights and Ace Pilots
. After quite a bit of experimentation
by various aircraft designers, a French pilot called Roland Garros and a Dutch engineer called Anton Fokker independently came up with ways of mounting a machine-gun so that it could fire through the the arc of a propeller without striking the blades, making the job of aiming a gun while flying a plane much easier (and also making it easier for the pilot to clear frequent gun jams). Increasing airspeed and armor of later aircraft designs meant that More Dakka
was always needed: by the late 1930s eight
rifle-caliber machine-guns were required for interceptor aircraft, and soon autocannon were starting to replace some, then all of the machine-guns.
In the inter-war period air-to-air doctrine began to diverge with only a few countries (notably Italy and Japan) developing agile lightweight dogfighters (like the A6M Zero and G.50 Freccia) in the WWI tradition, while most countries bet on formations
of powerful and fast fighters with ground-attack capability (single-engined medium types like the German Bf109, Soviet Yak-1, and US P-40, and twin-engined heavy types like the German Bf110, British Whirlwind, Soviet Pe-2, and US P-38). Britain didn't really put much faith in the fighter aircraft at all and as a result didn't develop modern medium fighters such as the Hurricane and Spitfire until 1937 (some medium bombers like the Mosquito were also reinvented as heavy fighters).
Planes got faster, stronger, better-armed and more specialised but generally remained biplanes made of canvas and wood until the mid-late 1930s, when a new generation of aircraft started to emerge, spearheaded by Germany's emerging Luftwaffe
. Multi-engined monoplane bombers could outpace the best British and French fighters, and the Messerschmitt Bf109 fighter blew everything else away. The British responded just
in time with their Hawker Hurricane and Supermarine Spitfire, and held off the German attack, while the French, who were still in the process of upgrading their air force and hadn't had the time to deploy their more modern fighters, were over-run.
This indicates what the armies of the world were just starting to realize - Air Power was now all-important. This lesson was shown again and again during the course of World War II
, as traditional naval Battleships were sunk at Taranto and Pearl Harbor and the most important naval battles were between carrier aircraft. Many small Pacific islands which would otherwise have been bypassed in the fighting took on great importance as air bases.
Towards the end of the war, jet engines were developed, with the German and British air forces being the first to put jet aircraft into action. During the Korean War
, jets fought each other for the first time, but it wasn't until shortly afterwards that the next major development in air combat took place: The Guided Missile.
Guided missiles now meant that aircraft could kill each other from miles away without ever seeing each other. It also meant the decline of the traditional bomber, as a single laser-guided bomb could now destroy a bridge, factory, railway yard, etc that had previously required a whole lot of saturation bombing
At this same time, the first vertical take-off aircraft were developed. Most fell by the wayside, with only the very good Harrier and the very poor Yak-38 "Forger" making it to operational service.
The Vietnam War
was one of the first major wars to use guided missiles, but guns often ended up being used, as the early missiles were unreliable and US rules of engagement required visual identification before firing. The US had actually taken guns off its fighters, then realised their mistake and stuck them back on. It was also the first war that proved the deadliness of the surface-to-air missile: Vietnamese SA-2
batteries made life hell for bomber crews. The US countered by developing air-to-surface tactics in Wild Weasel missions
After that war, both sides focused on technology rather than speed. The United States developed stealth aircraft, becoming border-line unbeatable (for the time being) in an air war as a result.
Conventional fighter v. fighter combat has been rare in recent years.
Types of Military Aircraft
The most glamorous and high-profile aircraft in any given air force. There are numerous sub-types depending on their precise tactical role (interceptors, air superiority fighters etc.) but as a general rule they're fast, agile and armed to shoot down enemy aircraft. Known originally as "scout" or "pursuit" aircraft. Armed generally with one or two machine-guns during World War One
, progressing to six or eight during World War II
(sometimes with the addition of explosive-shell-firing cannon). Missile armament is standard these days, though a cannon of some sort is usually included for close-in fighting and for when you run out of missiles.
The top speed of fighter aircraft hit just over Mach 2 in the mid-1960s, then levelled out. Studies in Vietnam found that the high speed was useless in close-in combat (which generally stayed under 600 knots). Exceeding Mach 1 also makes you a big target for infra-red missiles.
There are very few aircraft these days solely dedicated to this task.
Six separate generations of jet fighter aircraft can identified:
- First generation- the early sub-sonic fighters, featured in the closing stages of WW2 and in Korea, such as the F-86 Sabre and MiG-15
- Second generation- early supersonic, with primitive guided weaponry. The US "Century Series" (F-100 to F-106) and the MiG-19 are examples.
- Third generation- Improved weaponry and speed. Includes the F-4 Phantom II, the Dassault Mirage, and the MiG-21.
- Fourth generation- Increasingly multi-role and improving the electronic equipment, as well as "air combat maneuvering", brought on by the lessons of Vietnam. The MiG-29 and Su-27 "Flanker", US "Teen Series" (F-14, F-15, F-16, & F-18) are of this vintage.
- Generation 4.5- Further improvements to electronics and weaponry, but not stealth. Most of the recent fighters, such as the later "Flanker" derivatives, the Saab 39 Gripen and the Eurofighter Typhoon. American and Russian air forces generally retrofitted these features to fourth generation aircraft rather than designing new ones.
- Fifth generation- stealth fighters. Only the F-22 Raptor (US) is in service at the moment, but will soon be joined by the F-35 Lightning II, while the Sukhoi PAK FA (Perspektivnyi Aviatsionnyi Kompleks Frontovoi Aviatsyi, or Advanced Tactical Frontline Fighter) has just begun flight testing. Even the Chinese have recently gotten into the field with the Chengdu J-20, though it's not exactly clear how far they've gotten with their design.
- There is significant criticism against the USA for marketing the F-35 as an air superiority fighter. Sure it can do the job, but compared to even fourth generation fighters (especially upgraded 4++ generation Sukhois) it's woefully underpowered - both in terms of thrust as well as turning rate, critical factors in air to air combat. Which is not that surprising since it was developed under the Joint Strike Fighter program.
- The Su-47 Berkut was only a demonstrator of the type, although elements will almost certainly feature in the final design of the PAK FA.
Dedicated bombers appeared during the final stages of World War One
- big, lumbering, multi-engined beasts with multiple machine-gun mounts for self-defence and many, many, many bombs in their bellies. Before that, the most heavily armed aircraft to ever exist(sporting as many as twenty-five guns!
carried obscene payloads of bombs and sometimes even other aircraft,
and were used for strategic bombing. However, they were used mostly for naval patrols instead of being dedicated bombers. Between the wars, the idea that "the bomber will always get through" led Britain and France to neglect their fighter forces with near-disastrous results. With the advent of the Cold War
, bombers gained a new role - they were the main delivery system for nuclear weapons and were designed to fly very low or very high to avoid detection. With the advent of ballistic missiles for nukes and guided missiles for conventional arms, the traditional bomber faded from service. They're still useful for some things - they can carry a lot of bombs a long way, so the US keeps some B-52s around in case saturation bombing is needed.
In the most recent conflicts, bombers have found new life and tactical importance as their role shifts from saturation bombing to air support. Their long range translates into long loiter times and wide areas of coverage. Their high capacity means they can carry a wide range of different weapons in their bays all at once, suitable to provide whatever fire support the troops on the ground need. Bombers such as the B-1 and B-52 can hang out in an Area of Operations (AO) for eight or more hours at a time and quickly respond to trouble spots
The standard for "bombers" is high these days, with the International Institute of Strategic Studies setting a 10,000kg weapons load as the lower limit. About 8 aircraft (B-52, B-1B, B-2, Tu-22M, Xian H-6, Tu-95, F-15E and Tu-160) today qualify.
Sometimes these are dedicated aircraft (such as the famous Stukas and Sturmoviks of WW2
), other times they're just modified fighters. Ground Attack aircraft are designed for pinpoint surgical strikes on small moving targets that bombers aren't practical for, such as tanks, artillery, trains, infantry. During the two world wars, this was accomplished by flying very low and packing bombs, rockets, cannon and whatever else could be thought of. These days, Ground Attack aircraft have more or less entirely taken over the traditional strategic role of the bomber as well thanks to smart weapons. There's even a subcategory of the mission called "Wild Weasel
", where your whole objective is to go in first, thread your way through whatever array of ground-based anti-air defenses the enemy has up, and destroy it all, so that your pals can come in unmolested later. (See "Electronic Warfare" below for more details.)
Helicopters are often used for Ground Attack duties (the famous US Cobra and Apache types, for instance), as they can hover behind terrain before "popping up" and launching missiles, thus minimising the amount of time that the enemy can shoot back. Airplanes that share the role also share some performance characteristics: they tend to be small, nimble and relatively slow-moving. Perhaps the epitome of the role is the US A-10 Thunderbolt II, AKA the Warthog, which can't break the sound barrier, looks really
awkward, is built around a huge gatling gun
and can still fly with half the wings and engines shot off. Again, though, the advent of precision guided weapons means that just about any airplane can perform this role, because the pilot doesn't have to be smart; the bomb
does all the thinking.
One well known subtype of attack aircraft is the SVTOL (Short/Vertical TakeOff and Landing) attack plane. The most famous example is the US/UK Harrier. Planes with this capablity are generally used for ground support because they don't have the range or speed to go toe-to-toe with true fighters but their ability to land anywhere allows them to stay near the front lines in support of ground troops, and they can carry more weight (read: bombs, missles, and rockets) than most attack helicopers. That same ability also makes them popular as naval aircraft for countries without full-sized carriers.
Yeah, yeah. Not exactly glamorous, but stuff needs moving, and transport aircraft can move it quicker than boats. Just not as much of it at once. First used on a large scale during World War II
, notably for dropping paratroops and then resupplying them, and you'll often see them in footage from disaster areas where they fly in aid. Modern transport aircraft are often designed to be able to land on short and rough fields, allowing them to fly in aid (or troops if need be) to anywhere, not just somewhere with an airport.
Transport is also the other main job of the helicopter, which really can land pretty much anywhere.
Different "classes" of transport exist, but distinct "generations" of transport are less clear-cut as this is one role that an old, well-proven design can actually best a state-of-the-art, high-tech whiz-bang engineering marvel in.
- Light Transports - Single-engined workhorses like the still-used Antonov An-2 "Colt", a biplane powered by a single massive radial engine (piston power) and twin-engine small transports like the venerable C-47 Skytrain (Military version of the Douglas DC-3 Dakota, one of the most revered designs in all of aviation), and more recently turboprop planes similar to the small prop airliners used now for short-distance commercial flights, and biz-jet sized transports, these planes are for small loads. Not a lot of capacity but the things are dependable and effective. Basically the aviation equivalent to a moving-van. These aircraft carry no more than a few tons.
- Medium Freighter - Bigger than the light transport, but still able to operate from rough, short, unpaved or otherwise "rugged" airfields, this class is one of the few that can be truly described as synonymous with a single aircraft: the legendary Lockheed C-130 Hercules. Aviation's answer to the heavy mail van (the type of van UPS uses). Tough and noisy but it gets the packates delivered. These aircraft usually carry 15-35 tons of cargo, the legendary Hercules can carry 22.
- Tactical Heavy Airlifter - Despite the name, a class with freight capacity roughly equal to the Medium Freighter, but can travel a longer distance before needing to refuel. The C-17 could be considered an example of this, or the now-retired Lockheed C-141 Star Lifter. Sometimes used to transport a LOT of personnel at once. In the road vehicle weight comparison, one of these for personnel transport is the aviation version of a Greyhound bus.
- Strategic Heavy Airlifter - This one is the true heavy airlifter. Very few of these exist. The C-5 Galaxy for the Western World, and the Russian counterpart, the Antonov An-124 "Condor". Aviation counterpart to the semi-truck (a Lorry if you're British). These aircraft carry anything in the range of 70-150 tons. Recently, the development of Hybrid Airships(airships that are partially heavier-than-air, like a plane) in both DARPA and the Army, has shaken up the Strategic Heavy Airlifter niche, with their highly useful capability of carrying 2-5 hundred of tons of supplies and landing on any flat surface, all rather economically, albeit slowly.
As You Know
, Knowing is half the battle
. Reconnaissance was the first combat job undertaken by aircraft, and remains one of the most importance. Cameras have been used since the Great War, and remain the main plank of Recon to this day, though the cameras themselves have improved markedly. Some recon aircraft are purpose-built (think of "spy planes" like the U-2 and SR-71 Blackbird), but most are adapted from fighters or bombers. Of the purpose-built ones, the SR-71 is designed to go really fast and really high, whereas the U-2 goes really slow
and really high, having more in common with a glider than a powered aircraft. Nowadays, unmanned drone airplanes, helicopters and airships conduct surveillance in a variety of roles, ranging from hand-launched spyplanes to ultra-long-endurance high-altitude drone airships.
There is in fact a 34-nation treaty called the Treaty on Open Skies allowing unarmed recce flights over signatory countries to a set quota.
There are also ELINT (ELectronic INTelligence) aircraft, that listen in to communications or acquire radar information about the enemy.
AKA sub-hunting. Maritime patrol aircraft need to be big enough to carry sensitive sonar and magnetic detection equipment, and be able to stay airborne for long periods (it's not uncommon for them to carry two crews and rotate them). They are often converted airliners (such as the British Nimrod
, adapted from the Comet
airliner) or bombers (such as the Russian "Bear".) Most carry one or two torpedoes, though some, such as the US P-3 Orion, can carry as many as eight. They are particularly useful for antisubmarine warfare mainly because they travel much faster than submarines and the hunted sub can't shoot back. Indeed, most surface sailors would much prefer to stay out of torpedo range and let the flyboys do the work if it's at all possible. Blimps and airships were and are the preferred aircraft for this role, serving with spectacular success during WW1
and on through the Cold War, until the invention of the Nuclear Submarine rendered them obsolete.
Helicopters also do this job, and though their range is shorter and payload smaller, they can land on small frigates, destroyers, and cruisers, potentially giving a formidable antisub capability to almost every ship in a fleet.
Air-to-air refuelling tankers
Extending the range and endurance of other aircraft is very practical and these are very valuable "force multipliers". The US has by far the biggest fleet of these, although some other nations have a few. Converted from airliners, generally, they refuel other aircraft in-flight. This is not a 100% successful activity (one reason why this was never adopted for commercial aviation, despite some experiments). Examples include the KC-135 Stratotanker (a modified Boeing 707) and the Russian Il-78 "Midas". There are a number of methods of doing this.
Some ground attack aircraft and fighters carry "buddy stores", allowing to refuel other aircraft. More a Russian thing, as their tanker force has been historically poor.
Airborne radars / AEW&C
The acronym stands for "Airborne Early Warning And Control
." Again usually airships or converted airliners (although helicopters are used too), these aircraft, identifiable by the big saucer-like (or rod-like
) things often stuck on top of them, are used to monitor large sections of airspace (as in hundreds of thousands of square miles), vectoring in aircraft to do various things: hit this; don't hit that; be aware of enemies to the left; protect these friends; and keeping everyone up-to-date on how the battle's going.
The US E-3 Sentry is a particularly good example of this type, operated by the US, the UK and NATO on a collective level. The NATO Sentries form the entire Air Force of Luxembourg, despite being based in Germany. In other words, Luxembourg can't do much fighting itself... but boy can it call for friends.
With the advent of radar and surface-to-air missiles, preventing the enemy from locking onto a strike force became important. These aircraft, often converted fighters or ground attack aircraft, use powerful jamming devices to jam radar signals. Many also carry anti-radiation missiles, which home on radar sources and destroy the radars. You used to be able to stop these by just switching off your radar, but now they can remember their targets. The presence of these can force a SAM battery to not even take part in a fight. On the other hand, jammer aircraft tend to vulnerable to enemy fighters [[http://www.strategypage.com/htmw/htintel/articles/20090301.aspx?comments=Y
though there have been exceptions), and the development of SAMs with passive home-on-jamming features might change the game once again.
The first helicopter to achieve flight was the Focke-Wulf Fw 61 in 1936.
The earliest helicopters, limited by underpowered engines note
were not good for very much other than reconnaissance and maybe very light transport and medevac duties (like that chopper you see in every episode of Mash
). As the technology developed, the helicopters became more robust and could carry heavier payloads, which for a time mostly translated to carrying more people. They saw use in both the Army and the Navy due to their ability to hover over the ground and because they did not need runways or full-length flight decks like airplanes did. Later on, they began to mount weapons on them for self defense, then decided to mount more
weapons on them, to actively go after the enemy. The bulky transport designs were slimmed down to the sleek sexy attack choppers we know today (including the American Apaches and Cobras, and the Russian Mi-28's, Ka-50 Alligators and Ka-52 Black Sharks (known by the western militarys as the Havok, Hokum A and Hokum B, respectively
Helicopters, in their own way, fill many of the same niches that fixed-wing airplanes do, with a few exceptions. Helicopters rarely, if ever, engage in air to air combat, being designed primarily for air-to-surface roles. Also, there is a practical size limitation for how big you can make a helicopter before it's more trouble than it's worth, so they don't get used for strategic airlift. They can do a few tricks that most airplanes can't do, including hovering in place
or sling-loading bulky cargo underneath them. In various navies, they have replaced most ASW airships, and can hunt submarines or use their radar equipment from high altitudes to give the fleet a better ability to detect incoming threats, sometimes even going so far as to act as decoys to Taking the Bullet
draw anti-ship missiles away from the fleet.
Helicopters inherently have to expend energy to stay aloft, and as such they are quite Cool, but Inefficient
, burning fuel at a frightening rate. They are also inherently noisy, and cannot fly at very high altitudes, while simultaneously carrying only modest payloads and being exorbitantly expensive to buy and operate. These drawbacks are important to keep in mind, considering all of the unrealistic things helicopters are portrayed as doing in fiction, such as the Black Helicopter
, a trope devoted to using helicopters for extended, stealthy surveillance,
despite being arguably the worst
type of aircraft for the job.
You might have noticed a certain theme with how the American Army names their helicopters
: They are all named for Native American tribes (the UH-1 Huey is officially known as the "Iroquois"; there is no "Huey" tribe of Native Americansnote
). Navy, Marine, and Air Force helicopters do not follow this system as a rule, although airframes derived from Army helicopters will often feature similar names (the Navy "Seahawk" and the Air Force "Pavehawk" variants of the Army Blackhawk helicopter, for instance).
Airships were the first powered aircraft ever invented, coming into existence before the American Civil War,
and they have seen surprisingly extensive military use. In fiction, they are notable for having tons of Diesel Punk
and Steam Punk
cred, as well as being used to indicate alternate realities
or being just plain cool.
Airships are any steerable or powered aircraft that use buoyancy from lighter-than-air gases to get some or all of their lift. Expect nautical terms and themes
to be everywhere, in fiction and in real life. They're not called airships
Airships are poorly understood aircraft. If airplanes can be considered the Jack-of-All-Stats
or Fragile Speedster
of aircraft, and helicopters a Glass Cannon
, then airships would be roughly analagous to a Mighty Glacier
. They are only about 1/4 or 1/5 as fast as a jet airliner, or slightly slower than a helicopter, but they have the benefit of having the highest payloads of any aircraft as well as being the most durable
type of aircraft(when not filled with Hydrogen
) and have long endurance. Surprisingly, they're also quite cheap, relative to comparable aircraft, due to their mechanical simplicity. Their main drawbacks are their bulk, which makes landing difficultnote
and storage expensive. There's also the fact that foul weather, while easily survivable, ruins their speed and fuel efficiency, forcing them to either retreat or fly around squalls and hurricanes, similar to helicopters.
There are many types of airship, even more than there are types of airplane. Today, there are four main groups. Aerostats are the most common, airships which are moored to the ground with a tether and used for surveillance. These can be small or quite large, and often carry distinctive radomes and have inflatable fins. Blimps are non-rigid steerable balloons which use slight internal pressure to maintain their shape, and are still used, albeit more rarely than aerostats. Zeppelins, airships with external frames and internal cargo spaces, have almost died out completely in the military, but they were used extensively in the past, until Hydrogen gave Zeppelins bad rap.
The last kind of airship has just been recently invented, the Hybrid Airship, which can be a blimp or a Zeppelin, but is heavier-than-air. This allows them to carry truly gargantuan payloads, with the added safety margins of a plane and the efficiency and scale of an airship.
In fiction, airships in the military are often portrayed as Awesome, but Impractical
. However, their actual military role has been more Boring, but Practical
. This wasn't necessarily true in the early days of World War One
, because Zeppelins and airships were pressed into sometimes spectacular roles due to the simple nonexistence of alternative aircraft. They were used as heavy bombers, flying out in armadas to bomb cities. Even more spectacularly, they are the only aircraft capable of being a true Airborne Aircraft Carrier
. But their more common usage was to escort shipping, hunt submarines and conduct long naval patrols. Eventually their Hydrogen weakness was exploited by the invention of the incendiary bullet, and airships' true value as a defensive rather than offensive weapon was developed, in conjunction with the use of non-flammable Helium. By WW2
, airships were used to great effect, and continued to due so well into the cold war.
Today, airships are mainly used for surveillance, a role they are highly suited to. They are many times cheaper than drones and hundreds of times cheaper than satellites, but are often more effective than either because they can carry more payload and have much higher endurance. Their large payloads are also being developed for strategic heavy airlift, where their low speed is counterbalanced by their fuel efficiency and low cost.