Originally, it had been expected that the Cromwell would use the "High Velocity 75 mm" gun designed by Vickers but it would not fit into the turret. Development of the gun continued and as work commenced on the Comet, the gun design evolved into the 17 pdr HV (High Velocity). The gun now used the same calibre (76.2 mm) projectile as the 17-pounder but the cartridge case was from the older QF 3 inch 20 cwt anti-aircraft gun loaded to higher pressures. The resulting round was different from 17-pounder ammunition, being shorter, more compact and more easily stored and handled within the tank.