They were designed as a follow-on from the Porpoise class; physical dimensions were the same but stronger materials were used in hull construction and improved equipment was fitted.

[3] The Oberons operated during the Cold War, with duties including surveillance, tracking of other ships and submarines, delivery and retrieval of special forces personnel and serving as targets for anti-submarine training.

The submarines were built between 1957 and 1978 by four shipyards: Cammell Laird (4), Chatham Dockyard (6), Scotts Shipbuilding and Engineering Company (11) and Vickers-Armstrongs (6).

The bow caps and shutters are mechanically linked to a hydraulically operated drive rod from within the torpedo compartment.

[citation needed] The aft torpedo tubes passed through the ballast tank at the rear of the submarine.

A 31-inch (79 cm) section projected into the boat through the bulkhead, forming overall a relatively short tube of 12 feet (3.7 m), but of 25-inch (640 mm) diameter.

The diesel engines can only be operated with external ventilation, but this can be obtained either while on the surface or when shallowly submerged by use of two snorkels which can be raised from the fin.

[7] The generators are cooled by an internal fan on the shaft which circulates air through a filter and water-cooled heat exchanger within the casing.

The generator has one pedestal bearing fed with oil from the diesel engine lubrication supply and is fitted with an internal heater to prevent condensation when not running.

All steelwork within the battery compartments is lined with rubber to protect the metal from attack by acid, and also all conducting material is insulated to prevent risks of electric shock.

Waxed timber is used to make framing and crawlways to access the batteries and support them because of its resistance to acid.

Cooling water is fed through pipes attached to the electrode connectors to prevent overheating and the battery temperature is monitored.

Each armature also has an associated field winding which is separately supplied with current which may be varied resistively, providing further speed control (maximum 35 A).

Two 15 kW (20 hp) 60 Hz three-phase alternators provide power for equipment designed to work off 115 or 230 V AC and two more 15 kW 400 Hz generators provide power at 205 V AC used by radar, sonar, fire control, and communications electronics.

In the event of damage to the main electrical distribution system, provision is made for one of the CP generators to be connected directly to one armature of the port motor, to provide some propulsion by alternative circuitry.

In 1982, Onyx took part in the Falklands War, the only conventional submarine of the RN to do so, landing members of the SBS.

[14] In 1960 two options were presented to the Canadian government, the first suggesting the acquisition of expensive Barbel-class submarines and the second proposing the purchase of six cheaper Oberons as part of a larger package of vessels.

On 11 April 1962, the purchase was announced in the House of Commons of Canada by the Minister of National Defence, Douglas Harkness.

[22][23] The United Kingdom, in an effort to get the contract moving, offered the hulls of Ocelot and Opportune, but Canada passed on them.

All three boats received modifications to the original Oberon design, which included the enlargement of the snort de-icer, a different weapons fit, a larger air conditioning unit, active sonar and different communications equipment.

[30] In an effort to take the subs from anti-submarine warfare training to frontline service, Maritime Command developed a refit program that included new sonars, periscopes, communications and fire-control systems.

This included placing divers under the casing for further covert movement, or disembarking special forces teams using kayaks or inflatable boats.

Another two British Oberons were transferred to Canada: Olympus as a non-commissioned training vessel, and Osiris for spare parts.

The fin, outer hull, and stern section of HMAS Otway are preserved on land at Holbrook, New South Wales.

HMAS Otama is located off Crib Point in Westernport Bay, Victoria, where she has been awaiting conversion into a museum vessel since 2002; a lack of funding and co-operation from local and state governments means that the volunteer group hoping to preserve Otama attempted to sell the submarine on eBay but to no avail.

[40] She was moved to Port Burwell, Ontario in November 2012, and will become a focal point of a new Museum of Naval History.

One of the Brazilian Oberons (Tonelero) sank while docked at the navy yards at the Praça Mauá on Rio de Janeiro, on 24 December 2000.

[42] The Chilean Navy sold O'Brien to the city of Valdivia in 2002, to be converted into the first submarine museum of Chile.

The submarine went through a series of modifications in the ASMAR shipyards during that year, and as of December 2017, is on display at the end of Avenida Costanera Arturo Prat, in front of the Corte de Apelaciones building.

The Upholder-class submarines were later upgraded and sold to Canada for service in the Royal Canadian Navy after refit as the Victoria class, again replacing Oberons.