of 4.5-inch ammunition, at an average of 12 rounds per gun per minute, during one action in January 1941. QF Mark IV: used a two part (charge and shell) ammunition system. Designed for use by small warships. Fitted in mountings BD Mark IV, CP Mark V and UD Mark VI. QF Mark V: a further development of the Mark IV, designed for anti-aircraft use with remote power control (RPC, where the guns automatically train and elevate the target following the director) and a high rate-of-fire assisted by automatic ramming. Carried in the mounting UD Mark VI, with separate high-angle and low-angle hoists for the two types of ammunition (AA and SAP/HE) and a third for the cartridges. The rate of fire of the Mk V was 24 rounds per minute when power-loaded, 12–14 when hand-loaded, and up to 18 in burst mode when hand-loaded. Some 800 naval 4.5-inch guns of various marks were built. 474 guns were built for the army, all in 1939–41. During the 1950s, a change was made in weapons systems nomenclature which focused on the gun mount rather than the gun. Together with a change from Roman numerals, the Gun QF Mark V on mounting BD Mark VI became simply the Mark 6. The Mark 7 was never produced as the planned Malta-class aircraft carriers they would have been used on were never built. The majority of new escort vessels built for the Royal Navy in the 1950s and 1960s carried at least one Mark 6 mounting, with two in the Leopard-class frigates and County-class destroyers and three in the Daring-class destroyers. This gave these ships a level of firepower unprecedented only 15 years earlier. The Type 81 Tribal-class frigates were an exception, using reconditioned Mark V mounts from scrapped C-class destroyers that were fitted with RPC and known as the Mark 5* Mod 1. The evolution of the 45-calibre 4.5 inch gun family ended with the Mark V gun / Mark 6 mounting. It has been replaced by a new weapon of original design, the 4.5 inch Mark 8 with a 55 calibre-long barrel. Naval service Ships with 4.5 inch guns QF Mark I in twin mounting UD Mark III aircraft carrier HMS Ark Royal Dido-class cruisers and naval auxiliaries Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark II Reconstructed Queen Elizabeth-class battleships and Reconstructed Renown-class battlecruiser Illustrious-class aircraft carrier