British M-class submarine

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HMS M1
Class overview
Name	M-class submarine
Builders	Armstrong Whitworth, Vickers
Built	1916–1919
In commission	1920–1932
Planned	4
Completed	3
Cancelled	1
Lost	2
General characteristics
Displacement	1,594 tons (surfaced) 1,946 tons (submerged)
Length	295 ft 9 in (90.14 m) (M1 & M2) 305 ft 9 in (93.19 m) (M3 & M4)
Beam	24 ft 8 in (7.52 m)
Propulsion	2 × 12-cylinder Vickers 1,200 hp (890 kW) diesel engines 4 × 800 hp (600 kW) electric motors 2 × 3-blade 5 ft 10 in (1.78 m) diameter screws
Speed	15 kn (28 km/h) surfaced 8 to 9 kn (15 to 17 km/h) submerged
Range	Surfaced: 2,000 nmi (3,700 km) at 15 kn (28 km/h) 4,500 nmi (8,300 km) at 10 kn (19 km/h) Submerged: 17 nmi (31 km) at 9 kn (17 km/h) 80 nmi (150 km) at 2 kn (3.7 km/h)
Test depth	200 ft (61 m) - M2 accidentally reached 239 ft (73 m) in 1923
Complement	62
Armament	1 × BL 12-inch (304.800 mm) Mark IX gun (50 rounds) 1 × Mk II 3 in (76 mm) high angle anti-aircraft gun 4 × 18-inch (450-mm) (M3 & M4, 21 in (530 mm)) torpedo tubes (bow, 4 Royal Navy 18-inch (450-mm) torpedoes)[citation needed] (M1 & M2)
Aircraft carried	M2 converted to carry Parnall Peto seaplane

The British Royal Navy M-class submarines were a small class of diesel-electric submarines built during World War I. The unique feature of the class design was a 12-inch (305 mm) gun mounted in a casemate forward of the conning tower.

Due to the limitations imposed on submarine armament by the Washington Naval Conference, M2 and M3 had their guns removed. M2 was converted to carry a small seaplane and M3 was made into a minelayer.