High Quality Content by WIKIPEDIA articles! The QF 4.5 inch (113 mm) gun has been the standard medium-calibre gun used by the Royal Navy as a medium range weapon capable of use against surface, aircraft and shore bombardment targets since 1938. This article covers the early 45-calibre family of guns up to the 1970s. For the current unrelated 55-calibre Royal Navy gun, see 4.5 inch Mark 8 naval gun, manufactured by BAE Systems. Like all British nominally 4.5 inch naval guns, the QF Mk I has an actual calibre of 4.45 inches (113 mm). From the BL Mark I of 1916, the QF 4.7 inch gun (120 mm) was the mid-calibre weapon of choice for the Royal Navy, used particularly on destroyers. Apart from some ships armed with QF 4 inch guns due to supply problems, it remained the standard weapon for destroyers up to the W class destroyers of 1943. However, its usefulness as an anti-aircraft weapon had been limited by the failure to develop a mounting with elevation over 55°, the lack of a predictive fire control system in destroyer classes built prior to the introduction of the 4.7" twin mount, (see HACS) and the setting of fuzes by hand on early, prewar, mountings.