De Lisle carbine The De Lisle carbine or De Lisle Commando carbine was a British firearm used during World War II that was designed with an integral suppressor . That , combined with its use of subsonic ammunition , made it extremely quiet in action , possibly one of the quietest firearms ever made . Few were made as their use was limited to specialist military units . History . The weapon was designed as a private venture by William Godfray de Lisle ( known as Godfray ) , an engineer who worked for the Air Ministry . He made the first prototype in . 22 calibre ; this he tested by shooting rabbits and other small game for the table , near his home on the Berkshire Downs . In 1943 , he approached Major Sir Malcolm Campbell of Combined Operations with his prototype ; this was informally tested by firing into the River Thames from the roof of the New Adelphi building in London . This was chosen to discover if people in the street below heard the firing of the weapon . They did not . Combined Operations officials were impressed with the weapon and requested De Lisle produce a 9mm version . However , this was a failure . A third prototype , using the . 45 ACP cartridge that was favoured by de Lisle , was much more successful . Tests of this showed the weapon had adequate accuracy , produced no visible muzzle flash and was inaudible at a distance of . Subsequent official firing tests recorded the De Lisle produced 85 . 5 dB of noise when fired . As a comparison , modern testing on a selection of handguns has shown that they produce 156 to 168 dB when firing without a suppressor , and 117 to 140 dB when firing with one fitted . The de Lisle ' s quietness was found to be comparable to the British Welrod pistol . However , the Welrod was useful only at very short range and used fabric and rubber components in the suppressor that required replacement after a few shots . The de Lisle was able to fire hundreds of rounds before the suppressor required disassembly for cleaning . 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 . In 1944 , the Sterling Armaments Company was given an order for 500 De Lisle carbines , but eventually only produced around 130 . The Sterling version differed in a number of details from the earlier , Ford Dagenham version . Two prototypes of a further version , for Airborne forces , were made . These had folding stocks , similar to those fitted to the Sterling submachine gun . 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 ) . 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 . A number of De Lisles were shipped to the Far East and used during the Burma Campaign . The De Lisle would also be used during the Korean War and the Malayan Emergency . It has been claimed the weapon was also used by the Special Air Service during the Northern Irish Troubles . Description . The De Lisle was based on a Short , Magazine , Lee - Enfield Mk III * converted to . 45 ACP by modifying the receiver , altering the bolt / bolthead , replacing the barrel with a modified Thompson submachine gun barrel , and using modified magazines from the M1911 pistol . The primary feature of the De Lisle was its extremely effective suppressor , which made it very quiet in action . So quiet , in fact , that working the bolt to chamber the next round makes a louder noise than firing a round . The . 45 ACP was selected as its velocity was subsonic , it could therefore retain its full lethality when used with a suppressor ( supersonic rounds fired with suppressors generally have their power reduced , to avoid the crack of the bullet breaking the sound barrier ) . The Thompson gun barrel was " ported " ( i . e . drilled with holes ) to provide a slow release of high pressure gas into the suppressor that surrounded it . The suppressor , in diameter , went all the way from the back of the barrel to well beyond the muzzle , making up half the overall length of the rifle . The suppressor provided a very large volume to contain the gases produced by firing , this was one of the keys to its effectiveness . 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 . The single - shot , bolt operation offered an advantage in that the shooter could refrain from chambering the next round if absolute silence was required after shooting . A semi - automatic weapon would not have offered this option as the cycling of the bolt coupled with rearward escaping propellant gas would produce a noise with each shot . As silent as the carbine was , it was not very accurate . De Lisle ' s own . 22 prototype was given to the National Army Museum in London , but it was subsequently lost and its present whereabouts are unknown . A reproduction of the carbine is manufactured by the American company , Valkyrie Arms . Another company , Special Interest Arms , has announced limited production of a De Lisle replica which incorporates an improved magazine adapter system that allows the use of unmodified M1911 magazines and also fully supports the barrel chamber in the action .