When World War II started, silenced weaponary was an extreme rarity. As a result, in 1942, work was begun on the De Lisle Carbine, a totally silent rifle for use in covert operations. While there were initially several competing designs of the De Lisle, a version chambered in 0.45 ACP that used the magazine of a Colt M1911A1 and the stock and action of the Lee Enfield Mk.3 rifle was eventually used. Operating the bolt made more noise than firing a round. The De Lisle c.c. is still outstanding among silenced weapons, even now.
De Lisle Commando Carbine on Wikipedia