late 1940's vintage industrial heavy gauge steel m20 perforated artillery shell casing. fabricator unknown. the artillery-type spent shell was fired using a u.s. recoilless 75 mm caliber m20 rifle or gun. the pierced metal shell has been thoroughly cleaned and treated with a cleat coat lacquer to prevent the formation of surface rust. 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 propellent gases from the firing of a shell, to greatly reduce the recoil of the weapon. it is this use of vented propellent 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. two other shells available.