HMS K8 was a British K class submarine built by Vickers, Barrow-in-Furness. She was laid down on 28 June 1915 and was commissioned on 6 March 1917. K8 was sold on 11 October 1923. It had a complement of fifty-nine crew members and had a length of .
K8 displaced when at the surface and while submerged. It had a total length of , a beam of , and a draught of . The submarine was powered by two oil-fired Yarrow Shipbuilders boilers each supplying one geared Brown-Curtis or Parsons steam turbine; this developed 10,500 ship horsepower (7,800 kW) to drive two screws. Submerged power came from four electric motors each producing . It was also had an diesel engine to be used when steam was being raised, or instead of raising steam.
The submarine had a maximum surface speed of and a submerged speed of . It could operate at depths of at for . K8 was armed with ten torpedo tubes, two deck guns, and a anti-aircraft gun. Its torpedo tubes were four in the bow, four in the midship section firing to the sides, and two were mounted on the deck in a rotating mounting. Its complement was fifty-nine crew members.