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M18 recoilless rifle
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.〔''Jane's Infantry Weapons'' 1976 page 571.〕
== Origins and development ==
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.〔While many sources claim the pre-engraving on the M18 projectiles drive band in 1943 was a first, the Germans in World War I had this feature on projectiles for their famous Paris Gun. Later it was discovered that pre-engraving the band gave no advantage and future rounds were produced without this feature〕 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.〔Ian Hogg ''The Guns 1939-45'' page 151 Ballantine Books 1970.〕〔With most recoilless cannon, there is a 1-to-9 ratio—meaning that when the weapon is fired, 1 part of the propellant gases is used to force the shell forward and the other 9 parts of the propellant gases are expelled to the back to counter act that forward force, achieving a recoilless effect.〕
The "Kromuskit", as the new 57 mm weapon was called (a word play on the engineers' family names) was officially designated the T15 and first tested in November 1943. The tests proved that the Infantry Section's concept for a recoilless weapon was superior to the Artillery Section's concept and the development of the 105 mm weapon was canceled.〔''Weapons and Warfare'', p. 879, Vol. 8, 1978.〕 In late 1944, the T15 was redesignated the M18 57 mm Recoilless. The cannon and 57 mm ammunition were placed in mass production. Four types of ammunition were initially produced:〔The "T" designation was for experimental or early production shells and is similar to the modern "XM" designation. The "M" designation is used for standardized items.〕 an anti-tank HEAT round (T20E2 / M307), an HE round (T22 / M306), a Smoke (White Phosphorus) "bursting smoke" round (T23 / M308), and a Training Practice round.〔TM 9-1300-204, ''Ammunition for Recoilless Rifles'', p. 9, Washington: Department of the Army, 1959〕 By early 1945, over 2,000 M18 recoilless rifles and 800,000 rounds of ammunition were on order.〔Ian Hogg ''The Guns 1939-45'' page 151 Ballantine Books 1970.〕 After World War II ended, a canister round (T25E5) with a range of 175 meters was also produced.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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