HMS Opportune
Oberon-class
General Characteristics
Displacement:	2030t/2400t
Dimensions:	295ft x 26.6ft x 18ft (90m x 8.1m x 5.5m)
Armament:	8-21" (533mm) TT (6 bow, 2 stern. 24 torpedoes)
Propulsion:	2 shafts, two 3680bhp (2.7MW) Admiralty Standard Range diesel generators, two 12000hp (8.9MW) English Electric main motors = 12kts/17kts (22km/h/31km/h)
Range:	9,000 nautical miles (17,000km) at 12kts (22km/h)
Complement:	62 Later equipped to use Harpoon

The Oberon class were a thirteen ship class of diesel-electric submarines of the Royal Navy, and were based on the successful Porpoise-class submarine. The Oberons were far more successful in the export market than their predecessor, with fourteen boats being operated by Australia (HMAS's Oxley, Otway, Onslow, Ovens, Orion and Otama), Brazil, Canada and Chile.

The class differed from the Porpoises in that they had fibre glass in the casing and other additional improvements helped the class become even more silent than the Porpoises. Additional new electronics and weapons, including in 1970 the Mk24 Tigerfish torpedo. The RAN O-boats were upgraded to fire Mk48 torpedoes which could carry a nuclear ordinance. They were later updated to be equipped with the subsonic anti-ship Harpoon missile. HMAS Ovens was only the second conventional submarine in the world, and the first Oberon, to fire a sub-surface launched Harpoon missile. Consecquently, the boats designation changed from SS to SSG. This occurred off the island of Kawai in Hawaii in 1985, were the target was successfully hit from over the horizon. Like the previous Porpoises, the Oberons were far quieter than their American counterparts. They performed remarkably well in clandestine operations, performing surveillance and inserting special forces, vital during their heyday in the Cold War. These operations were primarily carried out by the British across arctic Europe, the Canadians across the arctic Pacific, and the Australians throughout S.E. Asia and as far north as the Sea of Japan.

The Oberons were arguably the best conventional submarine class of its time, with an astonishing reputation for quietness that allowed it to exist into the 21st century until replaced by newer classes such as the Collins and Victoria classes in Australia and Canada respectively. In fact, the ability of the O-boats to run in total silence enabled Australian submarines to successfully attack USS Enterprise, despite a huge number of supporting ships 'protecting' it.

The first of the class to be commissioned into the Royal Navy was Orpheus in 1960, followed by the nameship in 1961. The last to be commissioned was Onyx in 1967. Six were commissioned between 1967 and 1978 for the RAN. In 1982, HMS Onyx took part in the Falklands War, the only conventional submarine of the RN to do so. All Oberons in service, including boats exported, have now been decommissioned; the last RN boats decommissioned were in 1993.

Two ships have now become museum ships in the UK. HMS Onyx is now at Birkenhead, Merseyside, where another Falklands veteran, HMS Plymouth, is located. The other boat, HMS Ocelot, is located at Chatham. HMAS Ovens, an Australian Oberon, is now a museum-ship, located at the West Australian Maritime Museum at Fremantle, and Otway is preserved on land at Holbrook, NSW.

Note, some sources quote the complement as 68.