HMS Cachalot (S06) was a Porpoise-class submarine. Her keel was laid down on 1 August 1955 by Scotts Shipbuilding and Engineering Company at Greenock. She was launched on 11 December 1957, and commissioned on 1 September 1959.
The Porpoise class was the first class of operational submarines built for the Royal Navy after the end of the Second World War, and were designed to take advantage of experience gained by studying German Type XXI U-boats and British wartime experiments with the submarine , which was modified by streamlining and fitting a bigger battery.
The Porpoise-class submarines were long overall and between perpendiculars, with a beam of and a draught of . Displacement was standard and full load surfaced and submerged. Propulsion machinery consisted of two Admiralty Standard Range diesel generators rated at a total of , which could charge the submarine's batteries or directly drive the electric motors. These were rated at , and drove two shafts, giving a speed of on the surface and submerged. Eight torpedo tubes were fitted; six in the bow, and two in the stern. Up to 30 torpedoes could be carried, with the initial outfit consisting of the unguided Mark 8 and the homing Mark 20 torpedoes.
Cachalot attended the 1977 Silver Jubilee Fleet Review off Spithead when she was part of the Submarine Flotilla.
She was sold on 12 November 1979 for breaking up at Blyth.