HMS E18 was an E-class submarine of the Royal Navy, launched in 1915 and lost in the Baltic Sea in May 1916 while operating out of Reval.

British E-class submarines had fuel capacities of 50 long tons (51 t) of diesel and ranges of 3,255 miles (5,238 km; 2,829 nmi) when travelling at 10 knots (19 km/h; 12 mph).

On 14 July 1915 when at the mouth of the Ems deep in enemy waters Halahan brought E18 to the surface as he preferred the sea to using the toilet arrangements on board.

The fact E18 was surfaced wasn't passed on via Halahan's patrol report, he stated he was submerged at 20 ft, and an inquiry into submarine visibility from the air led E18 being painted in her camouflage scheme.

German minesweeping divisions were exploding mines during the time of the alleged attack which could explain what the crew of E18 heard while submerged.

She left Harwich on 28 August with her sister-ship HMS E19, first travelling to Newcastle to swing their compasses during which E19 burnt out one of her main armatures.

She dived into water only 23 feet (7 m) deep and — for almost three hours — progressed by crashing into the seabed and rising back up to break the surface.

After several hours resting in deep water she surfaced in the morning only to be fired on by the German cruiser Amazone; once again she dived to the bottom.

On returning, she encountered gale-force winds and icy conditions to the point where she had difficulty closing her conning tower hatch owing to ice.

No news whatsoever" By the 9 June E8's officers began collecting the belongings of E18's Halahan, Landale and Colson from their cabins.

Had it not been for the calm seas, it is likely she would have sunk from the damage; as it was, she was towed back to port with several of her crew killed, requiring major repairs.

Various sources record her simply as having been sunk on 24 May by a German decoy ship,[Note 3] though this clashes with the known attack on V100 on the 26th and the observations reported by Wilson and Goodhart in subsequent days.

[5] Three of E18's crew did not sail on her last mission; one, Jeremiah Ryan had measles and later transferred to E19; another, Albert Phillips, missed her patrol for unknown reasons.

The third was signalman Albert Edward Robinson who was replaced on this mission by E8's telegraphist George Gaby; he was later sent home in January 1917 and joined E4 on her recommissioning.

NB: 11 June 1916 is stated on the crew's papers as the date of being 'lost at sea', purely for administration purposes to close the books on E18, as the timing and circumstances of E18's loss were unknown.

In October 2009, the wreck of HMS E18 was discovered by a ROV deployed by the Swedish survey vessel MV Triad.

Photographs taken of the wreck show the submarine with its hatch open, suggesting that it struck a mine while sailing on the surface.