|Builder:||Cammell Laird, Birkenhead|
|Laid down:||23 October 1915|
|Fate:||Sold, 6 September 1922|
|Class and type:||E class submarine|
|Length:||181 ft (55 m)|
|Beam:||15 ft (4.6 m)|
HMS E42 was a British E-class submarine built by Cammell Laird, Birkenhead. She was laid down on 23 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.
Like all post-E8 British E-class submarines, E42 had a displacement of 662 tonnes (730 short tons) at the surface and 807 tonnes (890 short tons) while submerged. She had a total length of 180 feet (55 m) and a beam length of 22 feet 8.5 inches (6.922 m). She was powered by two 800-horsepower (600 kW) Vickers eight-cylinder two-stroke diesel engines and two 420-horsepower (310 kW) electric motors. The submarine had a maximum surface speed of 16 knots (30 km/h; 18 mph) and a submerged speed of 10 knots (19 km/h; 12 mph). British E-class submarines had fuel capacities of 50 tonnes (55 short tons) of diesel and ranges of 3,255 miles (5,238 km; 2,829 nmi) when travelling at 10 knots (19 km/h; 12 mph). E42 was capable of operating submerged for five hours when travelling at 5 knots (9.3 km/h; 5.8 mph).
E42 was armed with a 12-pounder 76 mm (3.0 in) 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-kilowatt (1.3 hp) power ratings; in some submarines, these were later upgraded to 3-kilowatt (4.0 hp) systems by removing a midship torpedo tube. Their maximum design depth was 100 feet (30 m) although in service some reached depths of below 200 feet (61 m). Some submarines contained Fessenden oscillator systems.
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- Koerver, Hans Joachim. Room 40: German Naval Warfare 1914-1918. Vol II., The Fleet in Being. Steinbach, Germany: LIS Reinisch, 2009.
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