In May 1939, the British War Office was informed of a submachine gun designed by Hungarian small arms designer Pal Kiraly. Kiraly had sent the designs to Birmingham Small Arms, who manufactured a pilot batch which they claimed only cost £5 per gun. The information was passed on to the Ordnance Board, who trialed a long-barreled version and a short-barreled version of the weapon. The long-barreled version used parts from the Swiss SIG MKMO submachine gun, including the magazines. The trigger mechanism was very complex and is shown below. It used a flywheel and spring to reduce the rate of fire. Although it was accurate and performed reasonably well during tests, the mechanism was far too user-unfriendly; in the words of Major Frank W. A. Hobart, "no soldier could have coped with this watchmaker's dream".
When approached, Kiraly agreed that if further interest was shown in the weapon, he could simplify the trigger mechanism. Despite this, the Ordnance Board never asked for any improvements on the design and so none were ever made. This prototype did, however, act as the forerunner to the Hungarian M39 submachine gun.