The boats were in active service when World War 1 (1914-1918) broke out in August of 1914. The force was assigned to convoy protection duty in Channel Waters as British ground forces made their way to France by ship for the fighting that lay ahead. There were also general patrols involving these boats in North Sea waters and around the Heligoland Bight (the bay located between Norway and Britain) in an effort to keep German forces contained. Before the cessation of hostilities, the boats were arranged as training platforms at Portsmouth for future submariners.
HMS D1 managed to survive the war but was sunk as a floating target in 1918. HMS D2, D3, D5 and D6 were all casualties of the war while HMS D4, D7 and D8 soldiered on for a time after the war.
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