1915
E18 entered service in the UK in 1915, commanded by Lieutenant-Commander R.C. Halahan. She joined HMS Maidstone on the 25 June 1915 and soon began North Sea patrols with the 8th Flotilla at Harwich. On her one and only patrol prior to leaving for the Baltic E18 departed Yarmouth with D7 and E13 on 9 July 1915. On the 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. While in this awkward situation a Zeppelin appeared, E18 dived to the sea bed but was easily visible from the air. E18 was then straddled with 12 bombs which caused no damage other than some embarrassment for Halahan in being caught unaware. 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. Strangely there is no German claim of an attack on a submarine - the Zeppelins in the air that day in this area were, L4, L6 and L7, none of which sighted a submarine let alone attacked one. L6 was the closest to E18's position when a Zeppelin was sighted but she moved away to the west when the explosions occurred. German minesweeping divisions were exploding mines during the time of the alleged attack which could explain what the crew of E18 heard while submerged.
E18 was dispatched to the Baltic as part of the British submarine flotilla in the Baltic. 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. After the delay to repair E19 they left Newcastle for the Baltic on 4 September at 1630 hrs. The two submarines separated and passed through the Oresund between Denmark and Sweden on the night of the 8-9th September. During the passage E19 at one stage found herself only metres from E18's stern and decided not to enter together. E18 encountered two German destroyers. 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 cruiser Amazone; once again she dived to the bottom. The German cruiser and attending destroyers then began to criss-cross over the top of E18 knowing her batteries would be very low. E18 had to sit it out on the bottom until the German left the area. E18 was lucky the German ships were not then equipped with depth charges. After escaping she was set upon by another two destroyers one of which came close to ramming her. On the 10 September 1915 Halahan sighted what he thought was the German battlecruisers Lutzow and Seydlitz and tried in vain to get into an attacking position, but in fact they were just two German destroyers as the German battlecruisers where not in the area at this time. On 12 September she met up with E19 and E9 off Dagerort, arriving in Reval (now Tallinn, Estonia) on the 13th. Halahan later wrote that entering the Baltic again should not be attempted unless absolutely necessary.
She operated out of Reval through the autumn of 1915. E18 departed on her first Baltic patrol on the 21 September 1915, next day on the 22nd she was in an excellent position to torpedo the German cruiser Bremen, a surfaced Russian submarine caused the Bremen to turn away just as E18 was about to fire and she missed her opportunity, she returned from this first patrol on 29 September 1915.
On 9 October 1915 E18 departed for her second patrol, by the 12 October she was in position to attack the pre-dreadnought SMS Braunschweig whilst patrolling off Libau (now Liepāja, Latvia), but her torpedo tube bow caps could not be opened, she then tried her beam tube but was forced to dive by German destroyers, when she did manage to get a torpedo shot off from her stern tube the range was too great and the opportunity passed. She returned to Reval on 16 October 1915 at 1700 hrs.
E18 departed for her third patrol on 9 November 1915, and was to patrol the Swedish trade routes, she arrived back at Reval on 15 November 1915 having sighted nothing of significance. During this patrol the crew had missed the visit of the Tzar.
Her fourth patrol was to patrol off Libau and try and find a way through the mine fields by following the courses of ships coming and going. She departed for this patrol on 30 November 1915 and returned on the 4 December 1915. This was her last patrol for 1915.