HMS E42 was a British E-class submarine built by Cammell Laird, Birkenhead. She was launched on 22 October 1915 and commissioned in July 1916. She served during the First World War, hitting with a torpedo the battlecruiser SMS Moltke on 25 April 1918 and making an unsuccessful attack on U-92 on 1 July 1918. E42 was sold for scrap at Poole on 6 September 1922.

Design

Like all post-E8 British E-class submarines, E42 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. E42 was capable of operating submerged for five hours when travelling at 5 kn. E42 was armed with a 12-pounder 76 mm 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.