At the start of the second World War the Thompson submachine gun was already an obsolete design. But it was also the only design available for use by Allied troops. Throughout the War, the government wanted to replace the Thompson with something that was lighter, cheaper, and faster to produce. This led to design submissions from many companies in different countries.
In 1939 the first design submitted for evaluation was the Hyde Model 35. George Hyde designed machineguns for Germany in the first World War. But his Model 35 submachine gun, bearing a close resemblance to the Thompson, proved to be inferior in several ways.
Hydes Model 35 was soon followed by the Spanish Star, the Finish Suomi, the Reising (from the Harrington & Richardson Arms Co.), the High Standard (from Gus Swibelius at High Standard Manufacturing Co.), a semi-auto carbine from Smith & Wesson, and the British Mark II STEN (named for its designers; Sheppherd, Turpin, and the Enfield Armory). Interestingly, even though the STEN was ultimately rejected by the Army, in a series of tests where the guns were rated on a scale of 100, the Thompson scored a 57, while the STEN scored an 88, highest of all guns tested.
Even though it was rejected, the British STEN had a profound affect on the U.S. military way of thinking. Unlike traditional military firearms, the STEN was cheap, crudely made, and ugly. It was a simple design of stamped metal welded together and painted. This was in stark contrast to American military firearms that were made from machined steel, blued or parkerized, and adorned with hardwood gunstocks.
The STEN represented a new breed of disposable submachine gun designed for the needs of modern warfare; battle at close range with high firepower. The British STEN, patterned after the German Schmeisser, and its sibling the Australian AUSTEN could be produced in vast numbers at the bargain basement price of about $10.
In 1942 the Army Ordnance Dept. took another look at the British STEN (Mark III). But again it was rejected. This time though, the Department told George Hyde, who had developed the unsuccessful M2 (submachine gun, not carbine) while working at the Inland Manufacturing Co. of Dayton Ohio, to design an all metal submachine gun as cheap and capable as the STEN. Amazingly Inland returned one month later with a prototype gun that met all the requirements. It was smaller, lighter, and could be made for under $20 in less than half the time. The gun fired at a much slower 400 rounds per minute, which the Army deemed as more desirable, and would eventually prove to be more reliable than the STEN.
On December 24, 1942, after one month of testing, the new gun was designated U.S. Submachine Gun, Caliber .45, M3. The Thompson and Inland M2 were downgraded to limited standard, and six months later the M2 was dropped entirely. In the summer of 1943 the M3 was put into production by the Guide Lamp Division of General Motors. But because of M3 production problems, Tommy Gun sales continued until February 1944. By the end of the War some 600,000 M3 Grease Guns were produced.