The Sten Mk4 was developed experimentally in 1943 for use by British paratroops. It used a remarkably awful folding stock along with a shortened receiver and barrel to make a very compact package – albeit one that must have been very uncomfortable to shoot. Several different models were made, with this one being a Mk4a(S) – the suppressed version. The suppressor is essentially the same system as used on the MkII(S), but with the rear endcap and barrel being permanently fixed to the receiver of the gun.
Only a small number (allegedly 2000) Mk4 guns were originally made, and they were used for testing only – never for field service. Virtually all were destroyed after the war, with a few remaining examples in British museums. This one was amnesty registered in 1968, and is almost certainly the only one in private hands in the US (and possible the only privately owned one in the world).
The Mk4 was dropped in favor of the Mk5, which was a much more effective gun and was used by the British paratroopers in the late days of World War Two.