Recoilless rifle

A recoilless gun or recoilless rifle (RCL) is a lightweight form of weapon that allows the firing of a heavier projectile than would be practical with a recoiling weapon. Technically, only devices that use a rifled barrel are recoilless "rifles". Smoothbore variants (those devoid of rifling) are termed recoilless "guns". This distinction is often lost, and both are often called recoilless rifles.

Normally used for anti-tank roles, the first effective system of this kind was developed during World War II. Recoilless rifles are capable of firing artillery-type shells at a range and velocity comparable to that of a normal light cannon, although they are typically used to fire larger shells at lower velocities and ranges. The near complete lack of recoil allows some versions to be shoulder-fired, but the majority are mounted on light tripods and are intended to be easily carried by a soldier.

Design

The typical recoilless gun functions very much like a conventional gun. The projectile and propellant are supplied as a single round and loaded into the breech. When fired, however, instead of all the propellant blast following the projectile out the barrel, a large portion is allowed to escape to the rear, providing an inertial force to counter the inertia of the projectile. Since recoil has been mostly removed, the heavy and complex gun carriage and recoil damping mechanism can be dispensed with. Despite the name, it is rare for the forces to completely balance, and real world recoilless rifles do recoil noticeably (with varying degrees of severity). Recoilless rifles are maintenance-intensive weapons, and if the breech and gas ports are old, damaged, plugged or poorly maintained, the recoil-dampening effect can be reduced or lost altogether, leading to dangerously powerful recoil.

Unlike a rocket launcher, which fires fin-stabilized rockets from a smooth bore, recoilless rifle rounds resemble conventional artillery shells. They generally have a rifling band to engage the rifled launch tube, spin-stabilizing the projectile, hence the term "rifle". The "case" area of the shell can be perforated to vent the propellant gases which are then directed to the rear, as the base of the shell disintegrates.

Since venting hot gases to the rear can be dangerous in confined spaces, some recoilless guns such as the Armbrust and MATADOR use a combination of a countershot, smoothbore barrel and pistons to avoid both recoil and back blast. The fin stabilized Armbrust "cartridge" contains the propellant charge between two pistons with the warhead in front of one, facing forward, and an equal countermass of shredded plastic in front of the other piston. Upon firing, the propellant expands rapidly pushing the pistons outward. This pushes the projectile forwards towards the target and the countermass backwards providing the recoilless effect. The shredded plastic countermass is quickly slowed by air resistance and is harmless at a distance more than a few feet from the breech. The pistons jam at the ends of the barrel trapping the hot propellant gases inside. All this allows safe firing in enclosed spaces.

The MOBAT 120mm recoilless rifle was a substantial piece of equipment that had to be towed behind a vehicle.The weapon was aimed via a spotting rifle, which fired much smaller projectiles whose trajectory matched that of the main weapon. Tracer rounds were fired first until hits were observed before firing off the main gun.

History

The first recoilless gun was developed by Commander Cleland Davis of the US Navy, just prior to the First World War. His design connected two guns back to back, with the backwards-facing gun loaded with lead balls and grease of the same weight as the shell in the other gun. His idea was used experimentally by the British as an anti-Zeppelin and anti-submarine weapon mounted on an Handley Page O/100 bomber and intended to be installed on other aircraft. During the Second World War the Swedish company Bofors Carl Gustaf developed a small 20 mm device, the "20 mm m/42"; the British expressed their interest in it, but by that point anti-tank rifles were already out of date.

In the Soviet Union development of recoilless weapons ("Dinamo-Reaktivnaya Pushka" (DRP), roughly "dynamic reaction cannon") began in 1923. In the 1930s many different types of weapons were built and tested with calibers ranging from 37 mm to 305 mm. Some of the smaller examples were tested in aircraft (Grigorovich I-Z and Tupolev I-12) and through some limited production and service, but development was abandoned around 1938, possibly as a side effect of Great Purge. The best-known of these early recoilless rifles was the "Model 1935 76 mm DRP" designed by L.V. Kurchevski. A small number of these mounted on trucks saw combat in the Winter War. Two were captured by the Finns and tested; one example was given to the Germans in 1940.

The first recoilless rifle to enter service in Germany was the "7,5 cm Leicht Geschütz 40" ("light gun" '40), a simple 75 mm smoothbore recoilless gun developed to give German airborne troops some useful artillery and anti-tank support that could be parachuted into battle. The 75 was found to be so useful during the invasion of Crete that a larger 105 mm version was developed on the same basic pattern. Interestingly both of these weapons were loosely copied by the US Army, reversing the flow of technology that had occurred when the Germans copied the Bazooka. The US did have a development program and it is not clear to what extent the design was copied, as there were in fact differences. The Japanese had also developed a portable recoilless anti-tank rifle which they had reserved for the defense of anticipated invasion of the mainland. As it was, however, these weapons remained fairly rare during the war though the US versions of the 75 started becoming increasingly common in 1945.

In 1947, the US 75mm was acquired as war surplus by the French military and mounted on a Vespa scooter. It was used by French paratroops as a mobile anti-tank and anti-fortification platform. It saw service in Algeria and Indochina.

By the time of the Korean War, recoilless rifles were found throughout the US forces. The "original" US recoilless rifles were the 57 mm and 75 mm, followed by a 105 mm. The new models replacing these were the 90 mm and 106 mm. The Soviets likewise enthusiastically adopted recoilless rifle (actually recoilless "guns" as they were smoothbore) technology in the 1950s, most commonly in calibers 73 mm, 82 mm, and 107 mm.

The British, whose efforts were led by Denis Burney, inventor of the "Wallbuster" HESH round, also developed recoilless designs. Burney demonstrated the technique with a recoilless 4 gauge shotgun. His "Burney Gun" was developed to fire the Wallbuster shell against the Atlantic Wall defences, but was not required in the D-Day landings of 1944. He went on to produce many designs including a man-portable 3.45" (88 mm) recoilless rifle, the Ordnance, RCL, 3.45 in pushed into experimental service in late 1945. Post-war work developed and deployed the BAT series of recoilless rifles culminating in the 120 mm L6 Wombat ("Weapon of Magnesium, Battalion Anti-tank").

Lightweight SPG-9 73 mm and B10 82 mm heavy recoilless rifles are still in service in the Russian army in airborne units, and are found quite commonly around the world in the inventories of former Soviet client states, where they are usually used as an antitank guns.

As the wire-guided missile became more and more popular in the late 1960s and early 1970s, the recoilless rifle started to disappear from the military except in areas like the Arctic where battery-powered Dragons and wire-guided TOWs would fail due to extreme temperatures. The former 6th Light Infantry Division in Alaska used the M67 in its special weapons platoons. The last major use was the Ontos tank, which mounted six of the US 106 mm on a light (9 ton) tracked chassis first developed for use by the US Army airborne troops in 1950. However the Army considered them useless, and the Marines picked them up instead, albeit only 176 of them. They used them to great effect as a fire support vehicle during the Vietnam War. The crews continued to report the Ontos was a very effective fighting vehicle in this role, but the military brass continued to argue for heavier designs, and in 1970 the Ontos was removed from service and most were broken up. However the recoilless rifle found other roles, most notably in the Indo-Pak confrontation in Kashmir, where it was used with great effect against bunkers and as artillery in otherwise inhospitable terrain.

Today one of several remaining front-line recoilless rifles in the armies of industrialized Western nations is the famous Carl Gustav recoilless rifle, an 84 mm man-portable anti-tank weapon. First introduced in 1946, it is still in widespread use throughout the world today, and has even been re-introduced into the US Marine Corps as an anti-bunker weapon. The US-made, M40 106 mm recoilless rifles, usually mounted on jeeps or similar small vehicles, are very common in the armies of many poorer countries, where they serve in the role of tank destroyers.

The 84 (Carl Gustav recoilless rifle) can be used, along with 66 (aka M72 LAW) and LAW 80 for Mouse-holing whilst fighting in built-up areas (FIBUA). This is where impromptu "doors" are added to a building to gain entry, hopefully avoiding the prepared defences of the occupiers.

The M-388 Davy Crockett used a recoilless rifle to launch a tactical nuclear warhead, deployed by the United States in the 1960s.

Older discarded 75 mm weapons are still used by the U.S. National Park Service as a system for avalanche control, a case of Swords to ploughshares.

ee also

*Newton's laws of motion
*List of artillery