Born out of The debacle of Dunkirk in 1940, The British Lancaster 19mm Sub-Machine Gun was envisioned as an Air Base Defense firearm that was designed to finally give The British Army a viable hand-held weapon. The British Army had gone thru many varieties of both home manufactured and “Lend-Lease” firearms from her Allies – with lukewarm to moderate success on the battlefield. Based in design pattern on the successful German Wehrmacht MP-28, The Sterling Armament Company set about to produce a variation of that weapon. Well made with a solid wooden stock (single piece), The M40 was 35-inches long with a reinforced, vented hand-grip barrel (8-inches). Weighing just slightly over 4-pounds, it was ideal for a close quarters, rapid fire gun. The 19mm round allowed for a cyclic rate of fire of 600-rpm, from a variety of ammunition clip styles (the standard Straight Clip and later 100-round “Drum” Magazine).
The M40 was accurate to 150-yards, but did feature the drawback of a non-selective fire ability. This meant it took some training for a Firer to learn to develop a “three round” burst pattern control style. Quickly replacing The US M1927 Thompson .45 Caliber Machine Gun, roughly 150,000 were produced and found their way into all Branches of The British Military, and it’s Commonwealth Allies. The reliable M40 remained in Service throughout the early 1970s.