Laid down of the shipyard of Vickers, Barrow in Furness in 1916, three years later launched and on 26 January 1932 during exercises lost in the Lyme Bay, Dorset, England. Part of the M-class submarines. After her sister ship the M 1 was lost in 1925 she and her other ships M 3 were used for experiments. Displacement 1,594 long tons/1.620 tons (surfaced)-1.946 long tons.1.977 tons (submerged) and as dimensions 90,14 x 7,52 metres or 295’9”x 24’8”. Fitted out with 2x12 cylinder Vicker diesel and four electric motors allowing a speed of 15 (surfaced)-8/9 (submerged) knots. Test depth 61 metres/200 feet. The crew numbered 62 men. The armament consisted of 1-12” gun, 1-3” anti aircraft gun and 4x18” bow torpedo tubes. Instead of the 12” gun was after 1925 a hangar placed to carry with her a Parnall Peto seaplane which conversion was completed in 1928. Colledge claims she was the former K. 19 renamed in 1917 and launched on 19 October a year later. At the dockyard at Chatham was in April 1928 the main gun removed and replaced by the hangar.
