 It was found that the only cartridge currently in service that was suitable for use with the lock was the .45 ACP round.Thompson then envisioned a "one-man, hand-held machine gun" in .45 ACP as a "trench broom" for use in the ongoing trench warfare of World War I. Payne designed the gun and its stick and drum magazines.The project was then titled "Annihilator I", and most of the design issues had been resolved by 1918; however, the war ended two days before prototypes could be shipped to Europe.