The Welrod was a program to develop a silent assassination pistol for British SOE (Special Operations Executive) late in 1942. It needed to be chambered in the .32 ACP cartridge, be effective to a range of 15m, and have its firing not recognizable as a firearm at 50m distance. The project was led by Major Hugh Quentin Reeves, who developed much of SOE's inventory of gadgets.

The Welrod concept was ready in January 1943, and it was not quite the Welrod that we recognize today. This initial MkI design used a fixed internal 5-round magazine and a thumb trigger, along with a rifle style bolt action mechanism. Samples were produced in April 1943, and testing showed that it was rather awkward to use. A MkII version was quickly developed in June 1943 with a more traditional style of grip and magazine, and formal trials led to the adoption of that MkII design. Incidentally, this is why the first Welrod produced was the MkII, and the later production version in 9mm was designated the MkI (it was the first mark of 9mm Welrod).

Eventually many thousands of Welrod pistols were manufactured, and they almost certainly remain in limited use to this day. This example we have today is the only surviving MkI example, however.

Many thanks to the Royal Armouries for allowing me to film and disassemble this unique prototype! 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/