HMS E21

HMS E21 was a British E class submarine built by Vickers, Barrow-in-Furness. She was launched on 24 July 1915 and commissioned on 1 October 1915. E21 was sold on 14 December 1921.

Design
Like all post-E8 British E-class submarines, E21 had a displacement of 662 LT at the surface and 807 LT while submerged. She had a total length of 180 ft and a beam of 22 ft. She was powered by two 800 hp Vickers eight-cylinder two-stroke diesel engines and two 420 hp electric motors. The submarine had a maximum surface speed of 16 kn and a submerged speed of 10 kn. British E-class submarines had fuel capacities of 50 LT of diesel and ranges of 3255 mi when travelling at 10 kn. E21 was capable of operating submerged for five hours when travelling at 5 kn.

E21 was armed with a 12-pounder QF gun mounted forward of the conning tower. She had five 18 inch (450 mm) torpedo tubes, two in the bow, one either side amidships, and one in the stern; a total of 10 torpedoes were carried.

E-Class submarines had wireless systems with 1 kW power ratings; in some submarines, these were later upgraded to 3 kW systems by removing a midship torpedo tube. Their maximum design depth was 100 ft although in service some reached depths of below 200 ft. Some submarines contained Fessenden oscillator systems.

Crew
Her complement was three officers and 28 men.