HMS Otter (S15)

The Oberon class was a direct follow on of the Porpoise-class, with the same dimensions and external design, but updates to equipment and internal fittings, and a higher grade of steel used for fabrication of the pressure hull.^[1]

As designed for British service, the Oberon-class submarines were 241 feet (73 m) in length between perpendiculars and 295.2 feet (90.0 m) in length overall, with a beam of 26.5 feet (8.1 m), and a draught of 18 feet (5.5 m).^[2] Displacement was 1,610 tons standard, 2,030 tons full load when surfaced, and 2,410 tons full load when submerged.^[2] Propulsion machinery consisted of 2 Admiralty Standard Range 16 VMS diesel generators, and two 3,000 shaft horsepower (2,200 kW) electric motors, each driving a 7-foot diameter (2.1 m) 3-bladed propeller at up to 400 rpm.^[2] Top speed was 17 knots (31 km/h; 20 mph) when submerged, and 12 knots (22 km/h; 14 mph) on the surface.^[2] Eight 21-inch (530 mm) diameter torpedo tubes were fitted (six facing forward, two aft), with a total payload of 24 torpedoes.^[2] The boats were fitted with Type 186 and Type 187 sonars, and an I-band surface search radar.^[2] The standard complement was 68: 6 officers, 62 sailors.^[2]

Otter was laid down by Scotts Shipbuilding and Engineering Company on 14 January 1960, and launched on 15 May 1961.^[2] The boat was commissioned into the Royal Navy on 20 August 1962.^[2] The only Oberon class submarine fitted with a mild steel casing needed when deployed as target for practice torpedo attacks.