M20 recoilless rifle
|M20 Recoilless Rifle|
|Type||Recoilless anti-tank weapon|
|Place of origin||United States|
|Used by||United States|
|Weight||103 lb (47 kg)|
|Length||82 in (2.1 m)|
|Barrel length||65 in (1.7 m)|
|Crew||1 or 2|
|Shell||75 x 408 mm R HE, HEAT, Smoke|
|Shell weight||20.5–22.6 lb (9.3–10.3 kg)|
|Caliber||75 mm (3.0 in)|
|Elevation||−27° to +65°|
|Muzzle velocity||1,000 ft/s (300 m/s)|
|Maximum firing range||3.9 mi (6.3 km)|
The M20 recoilless rifle is a U.S. 75 mm caliber recoilless rifle T21E12 that was used during the last months of the Second World War and the M20 extensively during the Korean War. It could be fired from an M1917A1 .30 caliber machine gun tripod, or from a vehicle mount, typically a Jeep. Its shaped charge warhead, also known as HEAT, was capable of penetrating 100 mm of armor. Although the weapon proved ineffective against the T-34 tank during the Korean War and most other tanks, it was used primarily as a close infantry support weapon to engage all types of targets including infantry and lightly armored vehicles. The M20 proved useful against pillboxes and other types of field fortifications. Its poor armor penetration by the HEAT round was because of it being a spin-stabilized projectile rather than the later fin-stabilized rounds used in the 106mm M40 recoilless rifle.
During World War II, the U.S. military recognized that, due to advancements in armor technology by enemy forces, a powerful lightweight weapon was needed to defend infantry and light armor units. The Ordnance Department Small Arms Division commenced development of a recoilless rifle and, by 1944, models of a 75 mm recoilless rifle were being tested. Production of the M20 was underway by March 1945; only limited numbers were used by Allied troops in the European and Pacific theaters.
The M20 relied on a perforated artillery shell casing, combined with a rear vented breech using propellant gases from the firing of a shell, to greatly reduce the recoil of the weapon. It is this use of vented propellant gases that eliminated the need for a recoil system, thereby reducing the weight of the launcher and enhancing its use as a light infantry weapon.
Recoilless rifles, such as the M20, were used successfully in large numbers by US forces during the Korean War; and by both sides in the First Indochina War (1946–54). They were phased out after being replaced by wire guided missiles, which were introduced during the Vietnam War in the 1960s and 1970s. Until stockpiles of ammunition were exhausted in the 1990s, M20 recoilless rifles were used to start controlled avalanches by the U.S. National Forest Service and National Park Service. 
China also produced an unlicensed copy, known as the Type 56, which was widely used by the North Vietnamese Army (NVA) and Vietcong guerrillas in the Vietnam War (1960–1975); there are also pictures suggesting its use by guerrillas and militias in the Lebanese Civil War (1975–1990), such as the Amal Movement militia.
- M18 recoilless rifle – smaller 57mm model of the same era
- M29 Weasel – the "M29C Type A" variant had a center mounted M20 as its armament
- Weapons of the Vietnam War
- Weapons of the Cambodian Civil War
- Weapons of the Laotian Civil War
- Weapons of the Lebanese Civil War
- Chamberlain, Peter (1975). Infantry, mountain, and airborne guns. Gander, Terry. New York: Arco. p. 58. ISBN 0668038195. OCLC 2067391.
- "75-77 MM CALIBRE CARTRIDGES". www.quarryhs.co.uk. Retrieved 2017-10-02.
- "United States Military Artillery for Avalanche Control Program:A Brief History in Time" (PDF). USDA Forest Service National Avalanche Center. Retrieved 2018-04-11.
- Anthony Cordesman (2016). After The Storm: The Changing Military Balance in the Middle East. Bloomsbury Publishing. p. 112. ISBN 978-1-4742-9257-3.
- A Toyota Land Cruiser BJ40/42 of the AMAL militia in 1984 armed with a Chinese made Type 56 75mm recoilless rifle.
- TM 9-2300 Artillery Materiel and Associated Equipment. dated May 1949
- TM 9-314 operators, and maintenance
- SNL C-74 parts
- The short film STAFF FILM REPORT 66-21A (1966) is available for free download at the Internet Archive
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