Royal Navy`s M class, sending the largest gun to sea By the outbreak of war in 1914, the majority of navies with submarines wanted a gun as an alternative to the torpedoes, but it was the Royal Navy which sent the largest gun to sea in a submarine with the M class. The thinking behind such a weapon was made clear by Rear Admiral Submarines "The object was to supplement torpedo attacks against surface ships, which could often elude a torpedo. A 12 inch projectile fired at fairly close range should be difficult to elude. Furthermore, fifty shells could be carried instead of a few torpedoes." The idea of a submersible battleship was first proposed in 1915, the proposal was to mount a 60 ton, 12 inch gun from a battleship in front of the conning tower. The scheme was eventually approved in February 1916 and four were ordered using the keels of K class boats, at that time constructed K-18 to 21. The M class was partly double hulled. The gun came from a Majestic/Colossus class battleship. The boats behaved well both on the surface and submerged and the gun was reliable even after being underwater for several hours. The first of class, M1, was not operational until April 1918 and never saw action.   Specifications, HMS M-1, M class: Displacement (srf/sub tons): 1,600/1,950             Dimensions (L*B*D feet): 296`0*24`6*18`9 Propulsion: 2*1,200hp Vickers diesel engine, 2*800hp electric motors for submergence driving two shafts Speed (srf/sub knots): 15.5/9.5 Range (srf/sub n/miles@knots): 3,800@10/80@2 Diving depth (feet): 150 Complement: 68 officers and enlisted Torpedo: 4*18" bow torpedo tube (21" in M-3), total of 8 torpedoes Mines: none Armament: 1*12" Mk XI main deck gun, 3" disappearing AA gun   Construction Four boats were ordered, M-1 and M-2 from Vickers Limited in Barrow launched April 1918 and November 1919 respectively, M-3 and M-4 from Armstrong Whitworth. M-3 was launched in 1920 and M-4 was canceled.   After the war the Washington Disarmament Treaty restricted the size of gun that could be mounted on a submarine to 8.5". M-2 and M-3 had their guns removed, M-2 was fitted as a seaplane carrier, and M-3 was converted to a minelayer. Back to History Index Image Country Year Description Lesotho 1999 British submarine of M class-interwar years