The Battle of May Island is the name given to the series of accidents that occurred during Operation E.C.1 in 1918.

Named after the Isle of May, a nearby island in the Firth of Forth, the "battle" consisted of a disastrous series of accidents amongst Royal Navy vessels on their way from Rosyth, Scotland, to fleet exercises in the North Sea. On the misty night of 31 January–1 February 1918, five collisions occurred between eight ships. Two K-class submarines were lost and three other submarines and a light cruiser were damaged. 105 British sailors in total died in the accidents.