M18 recoilless rifle

M18 Recoilless Rifle
M18 on a M1917A1 Tripod
Type	Recoilless anti-tank weapon
Place of origin	United States
Service history
In service	1945–1960s
Used by	United States Republic of China (Nationalist) People's Republic of China North Vietnam Philippines Tanzania
Wars	World War II Second Sino-Japanese War Chinese Civil War Korean War Vietnam War (limited)
Production history
Designer	Kroger and Musser
Designed	1942
Produced	October 1944
Variants	Type 36
Specifications
Weight	22.04 kg (48.6 lb)
Length	1.56 m (5 ft 1 in)
Crew	1–2
Shell	57×303mmR HEAT (5.64 lb (2.56 kg)) HE (5.3 lb (2.4 kg)) WP (5.66 lb (2.57 kg))
Caliber	57 mm (2.26 inches)
Action	Interrupted lug rotating breachblock
Recoil	Recoilless
Carriage	M1917A1 Machinegun Tripod Mount
Elevation	+65° to -27°
Traverse	360°
Muzzle velocity	365 m/s (1,200 ft/s)
Effective firing range	450 m (490 yd)
Maximum firing range	3.97 km (2.47 mi)
Sights	M26 2.8x Scope

The M18 recoilless rifle was a 57 mm shoulder fired anti-tank recoilless rifle used by the U.S. Army in World War II and the Korean War. Recoilless rifles are capable of firing artillery-type shells at reduced velocities comparable to those of standard cannon, but with greater accuracy than anti-tank weapons that used unguided rockets, and almost entirely without recoil. The M18 was a breech-loaded, single-shot, man-portable, crew-served weapon. It could be used in both anti-tank and anti-personnel roles. The weapon could be both shoulder fired or fired from a prone position. The T3 front grip doubled as an adjustable monopod and the two-piece padded T3 shoulder cradle could swing down and to the rear as a bipod for the gunner. The most stable firing position was from the tripod developed for the water-cooled Browning M1917 machine gun.

During World War II, the U.S. Army's Artillery Section was working on a 105 mm recoilless cannon, based on captured German models that used a plastic blow out plug in the cartridge case. At the same time, there was a freelance research by the U.S. Army's Infantry Section of a man-portable recoilless 57 mm cannon by two engineers, named Kroger and Musser. Instead of a blowout plug, the infantry section's recoilless cannon used a British development in which the cartridge case had hundreds of small holes in the side walls with a lining of plastic on the inside of the cartridge case walls to keep water and other elements out until the round was fired. Another unique innovation was the use of pre-engraving bands on the 57 mm projectile that engaged the barrel's rifling. The belief was this feature would reduce friction on firing, allowing more of the propellant gases to be used to force the shell towards the target and less being used to achieve the recoilless effect and therefore giving their design a much higher muzzle velocity than most recoilless cannon at that time period had achieved.