BL 7.5-inch Mk II – V naval gun
The BL 7.5-inch Mk II–Mk V guns were a variety of 50-calibre naval guns used by Britain in World War I. They all had similar performance and fired the same shells. History. Mark II. Mark II guns were originally developed to suit India's coastal defence requirements. During World War I several reserve guns made for India but still in the UK were employed as coastal defence guns in the UK. They were scrapped or sent to India soon after the war. Marks II*, II**, V. These were built  and employed specifically as naval guns and were mounted as secondary armament as a heavier alternative to 6-inch guns, on the following ships : Mark III. Mark III guns were built by Elswick Ordnance to arm the battleship "Constitución" they were building for Chile. Britain acquired them by default when she bought "Constitución" in 1903 to avoid the risk of the ship being acquired by Russia. "Constitución" became HMS "Swiftsure" in British service. "Swiftsure" was decommissioned in 1917 and her guns were used for coast defence in Britain, as siege guns on the Belgian coast near Nieuport for attacking German  batteries, and on "M15"-class monitors. Mark IV. Mark IV guns were made by Vickers for the battleship "Libertad" they were building for Chile. Britain acquired them by default in 1903 when she bought "Libertad" together with "Constitución". "Libertad" became in British service.