Thompson Submachine Gun
The Thompson submachine gun was named for its inventor, US Brigadier General John Tagliaferro Thompson, who spent most of his career as an Ordnance officer involved in small arms manufacture and design. After retiring in 1914 he was recalled to service during the First World War, On his own time, he devoted himself to the idea of designing a fully automatic rifle - without using gas operation (which he considered too complicated), recoil operation (which he considered too heavy) or blowback operation (which he considered too weak for military calibres). He settled on a locking system patented by Commander Blish of the US Navy, and with Blish set up the Auto Ordnance Company.
The Blish locking system used inclined faces which locked under pressure, and unlocked when pressure in the action released (when the bullet of the cartridge left the barrel, pressure in the action would release the bolt). While the Blish system was useless with rifle cartridges, it worked well with low-powered pistol size ammunition. Thompson retired again 1918, and his new weapon was not perfected in time to be used in World War One. He had nicknamed the weapon a "Trench Broom", but with the war's end it was decided to market the weapon for police use, and Thompson himself invented the name "sub machine gun."
The M1921 was designed in five different calibres, but it appears only .45 calibre was produced. Few militaries noticed the many variations on the .45 M1921, and the gun became a favourite among gangsters and criminals in the United States. Not until the US Marines used the weapons in Central America did the weapon receive military attention. The son of the original financier of Auto Ordnance sold the company in 1938 to a shrewd investor who thought that impending war in Europe would boost sales. Both the French and the British governments placed orders, as did the US government in 1940.
The service version of the M1921 was the M1928A1 and was expensive, but the gun was well loved by troops who used it in the field. It was regarded as accurate, reliable, and the large .45 cartridge was considered a "man stopper." The M1 version appeared in 1942, much simplified.
The Canadian Army adopted the Thompson after the fall of France, and eventually armed section commanders in infantry platoons with the weapon. All troops in the United Kindgom adopted the Thompson, and the weapon first saw Canadian combat use in Hong Kong in December 1941. In 1942 the Sten Gun - which was much cheaper to produce - began to replace the Thompson. However, all troops going to the Mediterranean continued to use the Thompson exclusively and the Sten Gun was not used at all in that theatre, due to logistical concerns (while .45 calibre ammunition was being supplied to the US forces in theatre, adding the Sten Gun to the Commonwealth arsenal would have provided an additional requirement for 9mm ammunition - no other weapons in theatre at that time used that calibre).
The gun could be fitted with a large 50 round drum magazine, which was sometimes done in Canadian service, but these drums were very heavy, made the gun bulky, and was too noisy for patrol work. Twenty and thirty round box magazines were the norm. The M1928A1 version had a pistol-type foregrip, and the Thompson also had a removable buttstock which made the weapon more compact.