HMS M4 (1919)

HMS M4 was an M-class submarine of the Royal Navy, built by Armstrong Whitworth at Newcastle upon Tyne and laid down in 1917. She was launched on 2 July 1919 but was never completed: the boat was cancelled and sold as an incomplete hulk on 30 November 1921. The M class was a large submarine type designed around a single 12-inch gun, and M4 as designed was to displace 1,594 long tons surfaced and 1,946 submerged, to be 305 feet 9 inches long and to carry 62 crew, with twelve-cylinder Vickers diesel engines, four electric motors and four 21-inch bow torpedo tubes. Her Wikipedia article is a short stub, so little more of her history is recorded.