HMS K7 was a K class submarine built by HM Dockyard, Devonport. She was laid down on 8 November 1915 and commissioned in July 1917. K7 was the only one of the disastrous K class to engage with an enemy; on 16 June 1917 she fired a salvo of torpedoes at the U-boat U-95 and scored a direct hit. However, the torpedo failed to explode with what has been described as typical "K" luck; K-7 escaped retaliation by steaming away at speed. K7 was involved in an accident with the 4th Light Cruiser Squadron. She was also involved in the catastrophic series of accidents during a night exercise that came to be known sarcastically as the Battle of May Island; K7 was damaged by running over the sinking HMS K4. K7 was sold on 9 September 1921 at Sunderland.

Design

K7 displaced 1800 LT when at the surface and 2600 LT while submerged. It had a total length of 338 ft, a beam of 26 ft, and a draught of 20 ft. The submarine was powered by two oil-fired Yarrow Shipbuilders boilers supplying one geared Brown-Curtis or Parsons steam turbine that developed 10,500 ship horsepower (7,800 kW) to drive two 7 ft screws. Submerged power came from four electric motors each producing 350 to 360 hp. It also had an 800 hp diesel engine to be used when steam was being raised, or instead of raising steam. The submarine had a maximum surface speed of 24 kn and a submerged speed of 9 to 9.5 kn. It could operate at depths of 150 ft at 2 kn for 80 nmi. K7 was armed with ten 18 in torpedo tubes, two 4 in deck guns, and a 3 in anti-aircraft gun. Its torpedo tubes were fitted to the bows, the midship section, and two were mounted on the deck. Its complement was fifty-nine crew members.