The Sten gun was Britain’s answer to a serious shortage of arms at the time of the Battle of Britain. As a response to the shortage, they came up with a submachine gun that ultimately carried the British all the way through World War II. The Sten gun is an example of what can be done in a hurry with relatively common tools and primitive materials, and still produce effective weapons if one is willing to put quality where it's needed. The gun proved to be extremely reliable, with tens of thousands of them being dropped to troops from the air into occupied Europe.
Learn more about the British Sten Machine Carbine in the “I Have This Old Gun” segment from a recent episode of American Rifelman TV.