M20 recoilless rifle

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 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. 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. The M20 was one of the main anti-tank weapons used by the U.S. military in the early days of the Korean War along with the 2.36-inch Bazooka. However, the recoilless rifle failed to destroy any North Korean T-34-85 during the Battle of Osan on July 5, 1950. After the deployment of the 3.5-inch M20 Super Bazooka in mid-July, the M20 recoilless rifle no longer functioned as an anti-tank weapon, and was used as an infantry support weapon.