[6] In 1943, he approached Major Sir Malcolm Campbell of Combined Operations with his prototype; this was informally tested by firing the weapon into the River Thames from the roof of the New Adelphi building in London.

[7] Combined Operations requested a small production run of De Lisle carbines and an initial batch of 17 were hand–made by Ford Dagenham, with Godfray De Lisle himself released from his Air Ministry duties so he could work full-time on the project; this initial batch was immediately put into combat use by the British Commandos.

[7] During the remainder of World War II, the De Lisle carbine was mainly used by the commandos, although they also saw some use by the Special Operations Executive (SOE).

[11] E. Michael Burke, the American former commander of a Jedburgh Team, stated that a De Lisle was used by them to assassinate two senior German officers in 1944.

[11] US Army Special Forces - MACV-SOG used the weapon for many years in the Vietnam War, according to MSG Reinald "Magnet Ass" Pope in a 2024 interview.

The silencer reduced the sound of the firearm discharging to such a degree that working the bolt (to chamber the next round) produced a louder noise than firing a cartridge.

[14] The .45 ACP cartridge was selected as its muzzle velocity is subsonic for typical barrel lengths; consequently it would both retain its full lethality and not require custom-loaded ammunition to use with a silencer.

The bolt operation offered an advantage in that the shooter could refrain from chambering the next round if absolute silence was required after firing; a semi-automatic weapon would not have offered this option as the cycling of the bolt coupled with rearward escaping propellant gas and the clink of the empty case against any hard surface would produce a noise with each shot.

[17] In 1970, MAC developed a 9 mm carbine called the "Destroyer",[18] inspired by the need for a silenced weapon to be used in special forces missions during the Vietnam War.