The Sten gun was designed by RSAF Senior Draftsman (sorry, Draughtsman) Harold Turpin in December, 1940. He sketched out a simple trigger mechanism on December 2, showed it to Major Reginald Shepherd the next day, and then finished out the rest of the submachine gun design that week. The first prototype gun was completed on January 8, 1941 and it was tested by the Small Arms School that same month. The design was approved for production (alongside the Lanchester) March 7th, 1941 and the first of 300,000 Sten MkI guns was delivered to the British military on October 21, 1941. The MkI and MkI* Stens were all manufactured by the Singer sewing machine company in Glasgow, with three contracts for 100,000 guns each issued in 1941.

The Sten was the British response to a dire need for a large number of cheap infantry weapons, and it served that purpose well. The MkI was quickly followed by a somewhat simplified MkI*, which discarded the unnecessary flash cone and the wooden front grip. An even simpler MkII optimized for mass production followed, along with a MkIII. As the end of the war approached the MkV was introduced which had much improved handling, and it would remain in service until the 1950s, when it was finally supplanted by the Sterling.

Many thanks to the Royal Armouries for allowing me to film and disassemble these rare submachine guns! The NFC collection there - perhaps the best military small arms collection in Western Europe - is available by appointment to researchers:

https://royalarmouries.org/research/national-firearms-centre/

You can browse the various Armouries collections online here:

https://royalarmouries.org/collection/