HMS H42

HMS "H42" was a British H class submarine built by Armstrong Whitworth, Newcastle Upon Tyne. She was laid down in September 1917 and was commissioned on 1 May 1919.
On 23 March 1922, "H42" was practising torpedo attacks against British destroyers steaming off Europa Point, Gibraltar, when she surfaced unexpectedly only 30 or 120 yards (27 or 110 metres) – sources differ – ahead of the destroyer . "Versatile", making 20 knots, went to full speed astern on her engines and put her helm over hard to port, but had not yet begun to answer her helm when she rammed "H42" abaft the conning tower, almost slicing the submarine in half. "H42" sank with the loss of all hands. An investigation found "H42" at fault for surfacing where she did against instructions.
Design.
Like all post-"H20" British H-class submarines, "H42" had a displacement of at the surface and while submerged. It had a total length of , a beam length of , and a draught length of . It contained a diesel engines providing a total power of and two electric motors each providing power. The use of its electric motors made the submarine travel at . It would normally carry of fuel and had a maximum capacity of .
The submarine had a maximum surface speed of and a submerged speed of . Post-"H20" British H-class submarines had ranges of at speeds of when surfaced. "H42" was fitted with an anti-aircraft gun and four torpedo tubes. Its torpedo tubes were fitted to the bows and the submarine was loaded with eight torpedoes. It is a Holland 602 type submarine but was designed to meet Royal Navy specifications. Its complement was twenty-two crew members.