Brigadier General Courtney Hodges, took the M1917 shell as the basis of the new prototype, trimmed off the brim and added a visor and skirt-like extensions to protect the back and sides of the wearer's head. Rejecting the conventional systems of cradles, the new helmet was given a Riddell type liner and suspension system, based on the contemporary style of football helmet, with an adjustable strap for the nape of the neck to prevent the helmet from rocking. The resulting prototype was designated the TS-3, and the McCord Radiator Company manufactured the first examples from Hadfield steel. In tests, they were found to be able to resist a .45 ACP pistol bullet fired at point-blank range, exceeding the initial specification. The TS-3 was given official approval on June 6, 1941 and was designated "Helmet, Steel, M1". Full scale production commenced almost immediately. Service Over 22 million U.S. M1 steel helmets were manufactured through September 1945. Production was done by McCord Radiator and Manufacturing Company and Schlueter Manufacturing Company; the former developed a method to create an almost eighteen-centimeter deep bowl in a single pressing, which was an engineering milestone at the time. Total production per year during the period 1941-45 : - 1941 : 323 510 - 1942 : 5 001 384 - 1943 : 7 648 880 - 1944 : 5 703 520 - 1945 : 3 685 721 In 1944, the stainless steel helmet rim with a seam at the front was replaced by a manganese steel rim with a rear seam, as well as the helmet bails being changed from a fixed, welded version to a swivel model in 1942, along with slight alterations to the shaping of the side brim. Further M1 helmets were manufactured for the Korean War. Production continued during the Cold War era with periodic improvements; in 1955 a grommet in the front of the liner was deleted, in 1964 the liner construction was changed to laminated nylon and a new chinstrap design was introduced in 1975. The final contract for US M1 helmets was placed in 1976. The M1 was phased out of US service during the 1980s in favor of the PASGT helmet, which offered increased ergonomics and ballistic protection. Following World War II, the M1 helmet was widely adopted or copied by numerous other countries and its distinctive shape was adopted as the NATO standard. Postwar analysis of wartime casualty