All eight D Class submarines were in commission at the start of the First World War, and took up station on the east coast of England, where their long-range potential was exploited to the full, with overseas patrols in the Heligoland Bight.
During the first three months of the war, two of the class were lost in the North Sea - D5 hitting a mine, and D2 going on patrol never to be heard of again.
Towards the end of the war, two more of the class were lost - D3 was accidentally sunk in the English Channel in March 1918, and three months later D6 was sunk by a U-Boat off the north coast of Ireland.
Of the remainder, D1 was sunk deliberately as a target in October 1918 whilst D4, D7 and D8 survived the war, to be taken out of service in July 1919, bringing to an end the great D Class era.
