Operation E.C.1, usually called by the sardonic name of the Battle of May Island, or sometimes the geographically correct Battle of the Isle of May, was a disastrous series of accidents amongst Royal Navy ships on their way from Rosyth in Scotland to fleet exercises on the misty night of 31 January to 1 February 1918. This saw the loss of two submarines, damage to three other submarines and a light cruiser, and the deaths of over 100 men, all of the Royal Navy. Although it took place during the First World War it was an entirely accidental tragedy and no enemy forces were present.
Here is a good summary account of the incident. There is an excellent more detailed account on World Naval Ships Forum. A dramatic photo of HMS Fearless, a light cruiser built in 1912, shows her minus most of her bow after ramming submarine K17. The submarine sank in a few minutes. Many of her crew managed to jump overboard before she sank, but 47 were lost.
Within 75 minutes, the submarines K17 and K4 had been sunk and K6, K7, K14, K22 and Fearless had been damaged and over a hundred people killed. The accident was kept secret during the war, and a memorial cairn was finally erected 84 years later, in 31 January 2002 in Anstruther harbour opposite the Isle of May.
The incident is also mentioned in a presentation given to the Forth Estuary Forum on “Wartime history beneath the waves“.
HMS Fearless after ramming submarine K17. Kindly provided by Clive Sweetingham. No known copyright restrictions.