British Air Ministry engineer William Godfray De Lisle came up with the concept of an integrally suppressed rifle while working at home in 1942. He created a prototype chambered in  .22 caliber and based on a Browning semi-automatic rifle to hunt small animals for food. After much success, he realized the extreme quiet of the rifle might fulfill his intended role for it, after all… Killing men.

In early 1943, he informed Sir Malcolm Campbell, head of the secretive Combined Operations, of his invention, and Campbell suggested an interesting way to demonstrate it – in the open with unsuspecting people around.

From the roof of a building overlooking the River Thames in London, De Lisle fired several shots into the water as people strode by on sidewalks. Campbell watched with interest to see if anyone heard the shots. None did. The weapon found a buyer right then. First, though, there needed to be improvements.

Combined Operations wanted a more potent caliber. Shunning rifle cartridges, a 9mm, the standard British and German pistol round, sounded right. De Lisle disagreed and suggested something larger: the U.S. .45 caliber pistol round. Denied, he created the 9mm version based on the standard Lee-Enfield bolt action. Subsequent testing showed reliability problems with the 9mm, and De Lisle, still insisting the .45 caliber the optimum choice, at last won over the officials and built the next version. This time, the tests went much better and established the De Lisle carbine as one of the quietest firearms in history.

35 inches long and weighing 7.8 pounds from stock to action, the carbine looked like a miniaturized Lee-Enfield rifle, then standard-issue in the British army. That is where similarities ended, for starting at the barrel, everything changed

De Lisle used a Thompson submachine gun barrel cut down to 8 inches, and ported it from the front of the chamber to almost the end of the bore. This bled gas from the already subsonic .45 bullet to where it emerged from the barrel still at lethal velocity, but without muzzle flash and almost without sound.

To give an idea of just how quiet it was, working the bolt to extract and chamber a fresh round made much more noise. The primary reason for this ability was the size of its silencer, a 2-inch diameter tube that extended well beyond the 8-inch barrel, to make up than half the length of the weapon. A forearm, which, like the stock, was made of wood, extended partway under the silencer and enabled the carbine to be handled like a rifle.

Feeding came from modified 7 or 11 round M1911A1 magazines. In testing, using the weapon’s iron sights gave the  .45 round gave adequate accuracy out to 50 meters, its most effective accurate range.  Theoretically, 200 meters was the stated maximum distance, but all knew that was wishful thinking with the .45. Besides, 50 meters was more than good enough for man-sized targets, and, even more important, the weapon still remained inaudible at that distance.

Combined Operations requested a small production run soon after trials, and Ford-Dagenham factory hand-built the first 17 examples under DeLisle’s direction. Once test-fired, the guns were packed and sent off to their first users, the Commandos

Initial reports from the field touted its efficiency. They did not realize it, but the De Lisle, along with the crude Welrod pistol, another purpose-built silenced model, gave the British the most efficient tools for clandestine killing the world had ever seen.

The 17 carbines continued service into 1944, when Sterling Armaments Company received a further order for 500. More improvements were made as well, though in the end only about 130 of the order saw production. Despite the low number, Special Operations Executive agents and Jedburgh teams obtained some of the guns, and it is known that two senior German officers, maybe its highest profile victims, were killed with one at some point in the year. And Europe was not the only place it harvested bodies.

In Burma, still only available in handfuls, the S.O.E. and S.A.S. employed them well, killing numerous Japanese sentries, and enabling missions, at least during the opening phase, to proceed quietly.

Meanwhile, back in Britain, work on a final model before the end of the war entered the prototype stage for airborne forces. The salient feature of this version was its folding stock. But the war’s end meant this variant never saw production, and the future of all De Lisle carbines was in doubt. The surviving examples lay dormant in armories used by the S.A.S and MI-6 when some were recalled to service in Korea, the Malayan emergency, The Troubles in Northern Ireland, and perhaps classified operations into the 1980s. Apart from photographs taken during World War II, only a few exist showing use beyond that, which plays into it and the Welrod’s reputation as tools for covert special killing.

The De Lisle shall remain an oddity. Few were made, ensuring that it stays a little-known weapon outside of WWII history books, where even there, it receives rare mention. While never a firearm expected to compete with the likes of a Garand, STEN, or Mauser, in its role it did the job, and according to those who used it, did it well.