The wreck of an early British submarine known as HMS/m D1, which was the forerunner to the Royal Navy’s patrol submarines that boosted Britain’s defensive power during the First World War, has been granted protection by the Department for Digital, Culture, Media and Sport on the advice of Historic England.

The wreck, off the coast of Dartmouth in Devon, was investigated in a project originated by U-boat historian Michael Lowrey, who was writing a book about First World War U boat losses. The wreck was identified by a team of technical divers who are skilled at diving at depths of over 40 metres, led by Steve Mortimer, diving from Wey Chieftain IV. They reported the discovery of HMS/m D1 to Historic England and it has now been protected by scheduling. This means divers can dive the wreck but its contents are protected by law and must remain in situ.

Multi-beam image of the newly- protected prototype of the D-Class submarine which was deliberately sunk off the coast of Dartmouth, Devon in 1918 and used as a target to test submarine detection equipment. Copyright Wessex Archaeology

HMS/m D1 was built by shipbuilding company Vickers at Barrow-in-Furness in Cumbria and was the secret prototype for the D-class, the Royal Navy’s first diesel powered submarine. Launched in 1908 and commissioned in September 1909, the D-class was a significant development on the C-class submarine, being larger and more powerful.

At the start of the First World War, HMS/m D1 was assigned to protecting the coast of Dover from enemy invasion before carrying out patrols outside of English territorial waters to monitor German shipping movements. In September 1917, HMS/m D1 joined the Portsmouth Local Defence Flotilla and a year later it was relegated to training duties. In October 1918, HMS/m D1 was decommissioned and scuttled- deliberately sunk. The submarine was used as a training target off the Devon coast for Royal Navy training exercises involving the detection of enemy submarines. The wreck sits upright and largely intact on the seabed.

Multi-beam image of the newly- protected prototype of the D-Class submarine. Copyright Wessex Archaeology

Duncan Wilson, Chief Executive of Historic England said: “The D-class submarine was superior to the C-class, with innovations that became integral parts of future Royal Navy submarines. These included diesel propulsion, twin propellers and a wireless telegraphy system which allowed the submarine to transmit and receive signals. This is a fascinating survival which deserves protection as an important part of our seafaring history.”

Lead Diver Steve Mortimer said: “Every diver dreams of identifying a historically important wreck.  Expecting to find the remains of a German U-boat, we were thrilled to discover a ground-breaking British submarine instead.  It’s tremendous that D1 is now protected but divers can still visit.”

Eight D-class submarines were built. HMS/m D2, HMS/m D3 and HMS/m D6 were sunk outside English territorial waters, while HMS/m D4, HMS/m D7 and HMS/m D8 were sold and scrapped in 1919. The wreck of HMS/m D5 is located off Lowestoft. Suffolk, and is protected under the Protection of Military Remains Act 1986.

For more information, please visit www.historicengland.org.uk