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.

[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] In 1990, Opossum took part in the bicentennial celebrations at Pitcairn Island, marking the occasion with a two-day visit in September.

[6] On 14 July 1993, Opossum (which was travelling on the surface at the time) collided with the fishing vessel Amber Rose off the coast of Scotland.

For his crest he chose "a Mouse Opossum Argent, the eye ring and claws Azure", while his heraldic motto is "Ipsis Fretis Impedimentis Possum".