High Quality Content by WIKIPEDIA articles! HMS M1 was a submarine of the British Royal Navy, one of four vessels of her class ordered towards the end of the First World War. She sank with the loss of her entire crew in 1925. The vessels were originally intended as coastal bombardment vessels but their purpose had been changed before detailed design began. M1 was fitted with a 12 in (300 mm) gun which was intended for use against surface ships in preference to torpedoes, the argument being that, "No case is known of a ship-of-war being torpedoed when under way at a range outside of 1000 yards".