[5] Then on 15 October 1914, she and E9 sailed from Gorleston in a successful attempt to penetrate the German defences and enter the Baltic.

On 18 October 1914, E1 unsuccessfully attacked the armoured cruiser SMS Victoria Louise in Kiel Bay.

[7] On 30 July 1915, she torpedoed and sank the German auxiliary minesweeper Aachen east-northeast of Östergarn, Gotland, Sweden.

[8] On 19 August 1915, she torpedoed and damaged the German battlecruiser Moltke (23,000 tons) during the Battle of the Gulf of Riga.

E1's service ended on 3 April 1918 outside Helsingfors (now Helsinki), 1.5 nautical miles (2.8 km) off Harmaja Light in the Gulf of Finland.