HMS M1: The Submarine With a Battleship's Gun

A Very Big Gun

In the First World War torpedoes were not very reliable. They ran too deep, they ran off course, and against a fast warship that saw them coming and turned away they very often missed.

British submarine captains in the North Sea had watched good attacks fail for exactly those reasons, and in 1915 the Admiralty began to consider a submarine that would not need torpedoes at all. It would carry a gun instead, and not a small one.

It would carry a 12-inch gun, the main armament of a battleship, firing a shell weighing the best part of 850 pounds, so that a submarine could come up within a mile or so of an enemy warship, fire one shot that no ship could dodge and no armour stop, and go back down.

The result was the M class, the only true "submarine monitors" the Royal Navy ever built. Four were ordered, but only three were completed. HMS M1 was laid down by Vickers at Barrow-in-Furness on 1 July 1916, as one of the steam-driven K class whose story is told in HMS K3, and her order was changed while she was on the stocks: she began life as K18.

She was launched on 9 July 1917 and completed on 17 April 1918, with diesel engines rather than steam, four torpedo tubes in her bow, and on top of her hull, forward of the conning tower, the long barrel of the gun.

How It Worked

The gun was fixed in a turret that could train only a little to either side, so the whole submarine had to be aimed at the target. It could be fired with the boat at periscope depth and only the muzzle of the barrel showing above the surface, and the idea was that she would stalk an enemy ship submerged, bring the muzzle up, fire and go down again within a minute or so.

The catch was that the gun could only be reloaded on the surface. M1 effectively had one shot at a time, and whatever happened to the first shell decided whether the attack had worked. Her designers thought one shot was all she would need.

The Navy is said to have been nervous about the idea for an unusual reason. If the Germans learned of it they might copy it, and a German submarine with a 12-inch gun was the last thing the Grand Fleet wanted to meet. Whatever the reason, M1 was not sent to the North Sea.

Max Horton

Her captain in 1918 was one of the most famous submariners in the Navy. Commander Max Horton had made his name in the first weeks of the war, when on 13 September 1914 his submarine E9 torpedoed and sank the German cruiser Hela off Heligoland, the first German warship ever sunk by a British submarine.

He went on to the Baltic and more success there, and when he took M1 to the Mediterranean in 1918 it was in the hope of finding something big enough to deserve her gun. He did not.

The Armistice came before she had fired a shot at an enemy, and in the next war Horton was the admiral who commanded the Western Approaches and beat the U-boats in the Battle of the Atlantic.

After the war M1 had a run of captains in quick succession, one of them in 1920 being Commander Hubert Vaughan-Jones, who had taken K15 to sea as her first captain in 1918. With the war over there was no enemy fleet left for a submarine monitor to ambush, and M1 became something of a curiosity, though she stayed in service.

Her sisters were converted: M2 into a submarine aircraft carrier with a hangar in place of her gun, and M3 into a minelayer. The idea of a gun-armed submarine came back once more in HMS X1, which was built at the start of the 1920s and armed with four 5.2-inch guns.

12 November 1925

On the morning of 12 November 1925 M1 was taking part in an exercise in the Channel off Start Point, on the south coast of Devon, under Lieutenant Commander Alec Carrie. She dived, and she never came back up. Aboard her were 69 men, among them Lieutenant Thorpe, the commanding officer of her sister M2.

For a while nobody knew what had happened. The answer came from Sweden. The Swedish collier Vidar had passed through the exercise area that morning, and her crew had heard two bangs, but nobody had seen anything and she carried on.

When she berthed in Stockholm, damage was found on her bow, and the paint on her stem was found to match the paint on M1. She had run over the submarine as M1 lay close below the surface and torn open her hull. M1 went straight to the bottom, and every man in her was lost.

Coming only four years after the losses of K5 and K15, it was a heavy blow to the Submarine Service.

The Wreck

M1 lies about thirty kilometres off Start Point in more than seventy metres of water, which put her beyond salvage at the time. A salvage company found the wreck in 1967, and in 1999 the wreck researcher Innes McCartney and his team dived her and confirmed her identity. She lies on her port side.

Parts of her conning tower and the gun mounting have fallen on to the seabed, and most of the great barrel is now buried in sediment, but her bow and stern are intact, and there are heavy dents in her starboard side and her conning tower. One hatch is open, through which some of her men may have tried to get out.

She is a war grave, protected by law under the Protection of Military Remains Act.

In 2025, a century after her loss, a team of technical divers led by Dom Robinson went down to her with the underwater photographer Rick Ayrton to record her and remember her crew. Coming up from her in a lumpy sea, Robinson reflected that her men must have survived some really dangerous times. They had.

The photograph at the top of this page shows M1 at sea in her wartime camouflage, with that extraordinary gun laid along her deck. Nothing like her had been built before, and nothing like her was built again.