HMS D8 was a British D class submarine built by Chatham Dockyard. The D class were based at Harwich, Immingham, Blyth and Dover. Their wartime role was to sink German warships. In the latter stages of World War I the D class were used for training crews based at Portsmouth. HMS D8 was laid down on 14th February 1910, launched 23rdrd September 1911 and was commissioned on 23 March 1912. She fought in the Battle of Heligoland Bight on 28th August 1914 along with sister ships HMS D2 and HMS D3. Then on 18th October 1914, she shadowed the German hospital ship Ophelia which was judged to be spying and was interned. She was sold on 19th December 1921 to H. Pounds.

During World War I the submarines patrolled the North Sea and the Heligoland Bight, and protected cross channel troopships. During the war, four submarines (D2, D3, D5, and D6) were lost, and the remainder (D4, D7, and D8) were paid off in July 1919.