closely and when the Mk.V was designed, the Americans followed suit with the A/N M3 but unreliability continued. After the war the United States Air Force (USAF) adopted a version of the M3 cannon as the M24, similar in most respects except for the use of the addition of electrical cocking, allowing the gun to re-cock over a lightly struck round. The problems of the American weapons led to most US fighters being equipped with the AN/M2 .50 cal Browning light-barrel machine gun throughout the war. Post-war development After the war, the Hispano variants disappeared fairly quickly as fighter armament due to the introduction of revolver cannon, based on the prototype versions of the un-built German wartime Mauser MG 213 design. The British introduced the powerful revolving 30 mm ADEN cannon in most of their post-war aircraft, while the French used the similar DEFA cannon, firing similar ammunition. The USAF introduced the 20 mm M39 cannon to replace the M24, while the Navy combined the original Hispano design with a lighter round for better muzzle velocity in the Colt Mk 12 cannon. As a ground vehicle-mounted gun, either anti-aircraft or as a general-purpose autocannon, the HS.404 lasted into the 1960s. A powered turret variant is still in production in Honduras and is used as a light anti-aircraft gun by the army and navy in several nations. The AN/M3 was developed into the Mk12 Colt 20 mm automatic cannon, one of the main weapons on boats of the Mobile Riverine Force in the Vietnam War and also used on some larger amphibious ships. Properties The Hispano fired a 20 mm diameter projectile from a long casing, the whole round weighing . Lengths of the projectiles varied with type but were set to variable depth in the casing to produce a total full round length of regardless of projectile type. The gun had a muzzle velocity between , depending on barrel length. Rate of fire was between 600 and 850 rounds per minute. The gun was long, weighing between . The British Mk V and American M3/M24 weapons were lighter and had higher rates of fire than the early HS.404 guns. Users France HS.404 Bloch MB.152 Breguet 693 Dewoitine D.500 Dewoitine D.520 Lioré et Olivier LeO 45 Morane-Saulnier M.S.406 Potez 631 UK & other Commonwealth countries Hispano Mk. I Gloster F.9/37—a design not taken into service Westland Whirlwind—the RAF's first cannon-armed fighter.