English Channel near Start Point in Devon after a collision with a Swedish collier, SS Vidar, on 12 November 1925. The wreck of M1 was discovered by a diving team led by Innes McCartney in 1999 at a depth of 73 metres. Later that year the wreck was visited again by Richard Larn and a BBC TV documentary crew, and the resulting film was aired in March 2000. M2 was converted to a seaplane carrier in 1925, a hangar replacing the gun turret. She was lost off Chesil Beach, Dorset, on 26 January 1932. It is thought that the hangar door was opened prematurely. M2 lies in shallow water, 32 metres deep with the top of the conning tower only 20 metres below the surface at low tide. She is a popular attraction for local scuba divers with as many as six boats anchored above her on busy days. M3 was converted to a minelayer in 1927 with stowage for 100 mines, primarily to test the mine-handling equipment of the Grampus class. The mines were carried on a conveyor belt which ran along her upper deck and was covered by an enlarged casing. The mines were laid through a door at the stern. She was scrapped in 1932 after the trials had been completed. M4 was broken up before completion. In 1924 all three completed members of the class were used to test hull camouflage to reduce the visibility of submarines to aircraft; M1 was painted grey-green, M2 dark grey and M3 was painted dark blue. See also Cruiser submarine References Martin H. Brice M-class Submarines, Outline Publications, 1983, D.K. Brown, The Grand Fleet, Warship Design and Development 1906-1922, Caxton Editions, 2003, External links RN Subs 1916 - 1932: M Class Innes McCartney on search for M1 and Affray Maidstone Sub Aqua 427 Gulls of War, October 1931 article in Popular Mechanics Submarine classes