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).

[1] When war was declared with Germany on 5 August 1914, E9 was based at Harwich, in the 8th Submarine Flotilla of the Home Fleets.

[4] At dawn on 13 September 1914, the submarine, commanded by Lieutenant-Commander Horton, torpedoed the German light cruiser SMS Hela six miles southwest of Heligoland.

E9 was scuttled outside Helsinki (Helsingfors) 1.5 nautical miles (2.8 km; 1.7 mi) off Grohara Light in the Gulf of Finland on 3 April 1918 to avoid seizure by advancing German forces.

While in command of the E9, Horton initiated the tradition of submarines flying the Jolly Roger upon returning from successful combat patrols.

Remembering comments by First Sea Lord Admiral Sir Arthur Wilson, who complained that submarines were "underhanded, unfair, and damned un-English" and that personnel should be hanged as pirates,[6][7] Horton flew the flag when the E9 returned to port following the sinking of the Hela.