WWII Grease Guns: How GM Helped GIs

By Frank Iannamico

The M3 submachine gun design had begun as the T-15 prototype, which was developed by the Ordnance Department and the Inland Division of General Motors. The three key individuals who shared much of the responsibility of the project were: Frederick Sampson, Chief Engineer of the Inland Division of General Motors; George Hyde, who had a number of original submachine gun and light-rifle designs to his credit; and U.S. Army Ordnance R&D officer Colonel René Studler. No submachine gun requiring extensive machining operations would be considered for adoption. The requirements called for an all metal weapon fabricated from sheet metal stampings to permit fast and inexpensive production with a minimum of machining operations, and no critical metals, such as aluminum, were to be used.

The original T-15 specifications of October 8, 1942, OCM 19007 were altered to include a kit to enable the weapon to be converted from its original .45 caliber to 9mm which was the standard pistol and submachine gun cartridge of the British and the Germans. Another amendment to the original T-15 design was the elimination of the semiautomatic function. This was done to simplify the design. The cyclic rate was such that semiautomatic fire could be accomplished by trigger manipulation. The new designation for the new 9mm/.45 full-automatic-only weapon was the T-20. Five prototype models of the T-20 and five 9mm conversion kits were built by General Motors for testing. The cyclic rate was relatively slow at 400 rounds per minute. There was very little muzzle climb. In the standard test of firing at a 6ft x 6ft target at 50 yards, the T-20 scored 97 hits out of a possible 100. This was a higher percentage than achieved by any other weapon tested in the trials except the Hyde-Inland M2.

U.S. Submachine Gun, Caliber .45, M3

The M3 submachine guns were all metal, fabricated mainly of stamped steel parts to take advantage of speed and economy of manufacture and assembly. Its weight distribution, along with its slow 350-400 rounds per minute cyclic rate, allow for excellent accuracy for a weapon of...

This article first appeared in Small Arms Review V23N2 (February 2019)
and was posted online on December 14, 2018


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