That's one quiet .45

The De Lisle was made in very limited numbers; 129 were produced during the period of 1942 to 1945 in three variations (Ford Dagenham Prototype, Sterling production and one Airborne prototype). Thompson submachine gun barrels were modified to provide the .45 calibre barrel, which was ported to provide a slow release of high pressure gas.

The suppressor, 2 inches (5.1 cm) in diameter, went all the way from the back of the barrel to well beyond the muzzle (the suppressor makes up half the overall length of the rifle), providing a very large volume of space to contain the gases produced by firing. This large volume was one of the keys to the effectiveness of the suppressor. The Lee-Enfield bolt was modified to feed the .45 ACP rounds, and the Lee-Enfield's magazine assembly was replaced with a new assembly that held a modified M1911 magazine. Because the cartridge was subsonic, the carbine was extremely quiet, possibly one of the quietest firearms ever made.

The De Lisle carbine was used by the British Commandos and other special forces during World War II and the Malayan Emergency. It was accurate to 250 metres (820 ft). -- Wikipedia.

Found at Sipsey Street