In the early 1940s he approached the British Ordnance Board with blueprints of a new submachine gun he had designed and patented.
It uses two rows of ammunition in staggered, double-stacked configuration. When the front stack of the magazine is full, a spring-loaded lever in the side of the receiver depresses the rear stack, allowing the bolt to bypass the rear stack and feed from the front. When the bolt retracts and ejects the last case fired from the front stack, the front follower rises into position and cams the lever out of the way, allowing the rear stack to rise, and the bolt to feed from it. This gave the weapon a great capacity for uninterrupted fire, while still maintaining a magazine of reasonable design and profile that could be loaded by hand.