HMS Grampus (S04) was a Porpoise-class submarine. Her keel was laid down in 1955 by Cammell Laird at Birkenhead. She was commissioned in 1958.

On April 1, 1963, Grampus returned to Gosport after spending three weeks under the polar icecap looking for holes in the ice. During the patrol it superficially damaged its hull on the ice.

On January 11, 1968, the French trawler Fomalhaut caught Grampus in its nets in the English Channel. Grampus surfaced and both crews spent over three hours disentangling the nets.

Grampus operated with USS Tigrone in a joint American-British oceanographic operation in the eastern Atlantic in 1972.

General Characteristics

• Displacement: 2,080 tons (2,113 tonnes) surfaced, 2,450 tons (2,489 tonnes) dived
• Length: 88.4 m (290 ft)
• Beam: 8.1 m (26.5 ft)
• Draught: 5.5 m (18 ft)
• Complement: 64 officers and men
• Armament: 6 x 21 inch (533 mm) bow torpedo tubes, 2 x 21 inch (533 mm) stern torpedo tubes; 30 torpedoes could be carried (usually Mk8 or Mk23) or mines
• Powerplant: Two ASR 16VVS AS21 diesel generators totalling 3680 bhp (2,740 kW), two English Electric main motors totalling 12000 hp (895 kW) driving two shafts, two 880 V batteries each of 224 cells
• Speed: 12 knots (22 km/h) surfaced, 17 knots (31 km/h) dived