During World War II the U.S. military recognized that a powerful lightweight weapon was needed for defending infantry and light armor units due to advancements in armor technology by enemy forces. The Ordnance Department Small Arms Division commenced development of the 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 on the European and Pacific theatres.

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 during the Korean War, but were phased out after being replaced by wired guided missiles introduced during the Vietnam War in the 1960s and 1970s. Currently, M20 recoilless rifles are being used as part of the avalanche control system used by the U.S. National Park Service. There are also pictures suggesting its use by guerrillas in the Lebanese Civil War