HMS M1 was fitted with a 12-inch gun for attacking coastal targets.
HMS M1 was a British M-class submarine launched during the First World War. Instead of relying mainly on torpedoes, it carried a massive 12-inch naval gun mounted in front of the conning tower. The weapon was intended to attack surface ships and coastal targets while the submarine remained difficult to detect.
The concept reflected naval designers’ search for ways to combine submarine concealment with heavy firepower. However, the gun could not be aimed independently in the same way as a conventional turret, so the submarine generally had to point its hull toward the target. This limited the weapon’s practicality.
M1 was lost in 1925 after being struck by the Swedish ship Vidar in the English Channel. The collision occurred while M1’s gun turret doors were open, and the submarine sank with its entire crew. HMS M1 is therefore remembered both for its unusual armament and for the danger of experimental submarine designs.