The wreck of a pioneering British submarine used to patrol the English Channel during the First World War has been granted protected status after it was rediscovered by divers.

The prototype long-range diesel submarine, known as HMS/m D1, was launched in secret from Barrow-in-Furness, Cumbria, in 1908 and was the first of the Royal Navy’s patrol submarines used to defend British waters and undertake longer missions.

The vessel was deployed off Dover at the outbreak of the First World War to deter a German invasion before later being used outside UK territorial waters to spy on enemy shipping movements. The D-class submarines had a number of valuable innovations, including being equipped with wireless telegraph to send and receive messages.

The D1 was eventually scuttled off Dartmouth in Devon in 1918 to act as a training vessel for submarine detection techniques. It was recently rediscovered as part of a project to trace sunk German U-boats and found by divers sitting upright and largely intact on the seabed.

Following a recommendation from heritage watchdog Historic England, the wreck site has been given scheduled status, meaning it can be visited by divers but its contents are protected by law.

Duncan Wilson, chief executive of Historic England, said: “This is a fascinating survival which deserves protection as an important part of our seafaring history.”

The D1 was the first of eight D Class submarines to be built, five of which were sunk with the remaining three eventually sold as scrap.

Steve Mortimer, the leader of the diving team which accidentally discovered the D1 while looking for a U-boat wreck, 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.”