E11 was one of the most successful submarines in action during the 1915 naval operations in the Dardanelles Campaign, sinking over 80 vessels of all sizes in three tours of the Sea of Marmara.

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] E11 joined the 8th Submarine Flotilla at Harwich following sea trials on 2 October 1914 under the command of Lieutenant-Commander Martin Nasmith.

Nasmith was deterred from breaking through the entrance to the Baltic by numerous vessels and warships in Swedish waters during a night passage.

Surfacing off the town of Gallipoli, Nasmith captured a Turkish sailing vessel and lashed it to the conning tower to act as a disguise.

The following day, near the port of Rodosto (today Tekirdağ), E11 encountered the Turkish transport Nagara, laden with ammunition.

Aboard the transport was an American journalist, Raymond Gram Swing, from the Chicago Daily News.

E11's attack on Constantinople, the first by an enemy vessel in over 100 years, had an enormous impact on Turkish morale, causing a panic in the city and compelling Goeben to shift to a safer mooring.

E11 returned to the Bosphorus approaches on 27 May and sank more ships, but running short of torpedoes and with mounting mechanical problems, Nasmith headed home on 5 June.

On his return passage through the Dardanelles he encountered an anchored transport near the Moussa Bank which, despite his vulnerable position and the poor state of the submarine, he attacked and sank with his final torpedo.

[15] Two days later 8 August 1915 as a new British landing was underway at Suvla, E11 torpedoed the antiquated Turkish pre-dreadnought battleship Barbaros Hayreddin off Bulair at the northern entrance to the Dardanelles.

Visiting Constantinople again, E11 sank a Black Sea collier Isfahan as it was preparing to unload — a significant blow as coal was the main fuel source and supplies were scarce.

Moving into the Gulf of Izmit, on the night of 20 August, E11's first officer, Lieutenant Guy D'Oyly-Hughes, swam ashore and blew up a section of the Constantinople–Baghdad railway line, a feat for which he was awarded the Distinguished Service Cross.