Oberon-class submarine

The Oberon class was a 27-boat class of British-built diesel-electric submarines based on the successful British Porpoise-class submarine.

Thirteen were constructed for the Royal Navy, while another fourteen were built and exported to other countries' navies: six to the Royal Australian Navy, three to the Royal Canadian Navy with an additional two British submarines later transferred, three to the Brazilian Navy, and two to the Chilean Navy.

As of 2006, at least fourteen Oberons are confirmed to have survived in some form: Seven as museum boats or tourist attractions, two preserved in partial form as monuments, while five are to be converted into museum boats, or are otherwise awaiting disposal.

Design and construction
The 295.2 ft long Oberon class was based heavily on the preceding Porpoise class of submarines, which were in service from 1956 to 1988. Changes from the Porpoise design were primarily to improve the strength and stealth of the submarine. Instead of UXW steel, the hull was built from QT28 steel, which was easier to fabricate and stronger, allowing the submarine to dive deeper. Glass-reinforced plastic was used in construction of the casing.

Electronics, sonar, and radar systems were also upgraded to the latest standard. The submarines were equipped with a Type 1002 surface search and navigation radar, a Type 187 Active-Passive attack sonar, and a Type 2007 long range passive sonar.

The Oberons were constructed at a variety of shipyards in the United Kingdom: the six Australian and two Chilean submarines by Scotts Shipbuilding and Engineering Company (the latter were built after the Scott Lithgow merger); the three Brazilian submarines by Vickers-Armstrongs; and the three Canadian submarines at Chatham Dockyard. Construction of the British submarines was shared amongst four dockyards: the three mentioned above and Cammell Laird.

Armament


The Oberons were originally armed with eight 21 in torpedo tubes: six tubes in the bow, and two short tubes for anti-submarine defence in the stern. The submarine normally carried a payload of 20 torpedoes for the forward tubes; a mix of Mark 24 Tigerfish and Mark 8 torpedoes, while only the two pre-loaded torpedoes were carried for the stern tubes. Naval mines could be carried instead of torpedoes: the torpedo payload would be replaced with up to 50 Mark 5 Stonefish or Mark 6 Sea Urchin mines.

The forward torpedo tubes are constructed in two sections bolted together across the bulkhead at the fore end of the torpedo compartment. The inner section of 116 in long is constructed of 0.5 inch rolled steel fitted with welded flanges and support brackets. The outer section is constructed of a similar tube 175 in long but with a reinforced 1.125 inch thick section behind the main bulkhead. The internal door hinges at one side with two locking mechanisms, a swing bolt opposite the hinge and a rotating locking ring attached to the tube which presses down on the ten projecting lugs around the door. The outer end of the tube is sealed with a domed bow cap. Bow shutters close across the bow caps so as to preserve the streamlined shape of the bow when the cap is closed. The bow caps and shutters are mechanically linked to a hydraulically operated drive rod from within the torpedo compartment. The bow cap opens first behind the shutter, which then folds back against it forming a smooth exit tube. Interlocks prevent the doors at both ends being opened at the same time but the inner door is also provided with a test cock to check whether the tube is full of water before opening and remains held nearly closed by the swing bolt after the locking ring is released. The tube internal diameter is 22.5 in, wider than the torpedo which is designed as a loose fit inside the tube. Torpedoes could either be fired electrically or with compressed air.

The aft torpedo tubes passed through the ballast tank at the rear of the submarine. There was a 31 in section projecting into the boat through the bulkhead forming overall a relatively short tube of 12 ft but of 25 in diameter.

Propulsion systems
The class use diesel electric propulsion with lead-acid batteries to provide power when the engines cannot be used. Each vessel has two Admiralty pattern V-16 diesel engines (ASR1 16VMS) each driving one 1280 kW 880V generator. These can provide power directly to the two 2000 BHP electric motors, one directly connected to each propellor, or for charging batteries. 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. One snorkel brings in new air to the boat while the other takes exhaust fumes from the engines. The ventilation system is designed so that the fresh air spreads through the boat.

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. There is a grill to allow pressure equalisation inside and out. 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.

The submarine has two batteries, each comprising 224 2V cells (type D7420) giving a nominal 440V output. One battery is located underneath the crew accommodation compartment, and the other under the control compartment. Each battery has a switch circuit in the middle so that it can be split into two banks of 112 cells. The cells are designed to deliver 7420 Ah over a period of 5 hours. 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. The battery compartment has a sump to collect any spilled liquids. Each cell weighs 1,120 lbs, measures approximately 4 ft by 16in by 12 in and contains 18.5 gallons of electrolyte. Cells are held tight in place with wooden wedges to prevent movement with the boat. Each cell has four connector bolts to each electrode and an agitator pipe which bubbles air through the cell to ensure the electrolyte remains mixed and uniform. Cooling water is fed through pipes attached to the electrode connectors to prevent overheating and the battery temperature is monitored.

In operation each battery is charged until the voltage reaches 560V, then allowed a further hour's charging. Fortnightly it should be allowed 5 hours charging after reaching 560V to ensure a maximum charge is reached. Every two months a battery should be given an equalisng charge of eight hours to ensure all cells have reached their maximum. The battery is designed to operate with a specific gravity of the electrolyte between 1080 and 1280. Initial charging current should be around 1650 Amps for sg below 1180, 1250A above 1180, falling to 280A when charging is complete. At a voltage around 538V the cells begin to give off explosive hydrogen gas, so the applied power is reduced during charging to keep voltage below this value until current falls to 280A. 280A is then maintained while voltage is allowed to rise until the requisite voltage and charge time is reached. In emergency, charging current can be raised to 2000A. To maintain overall capacity, batteries need to be completely discharged over a 5 hour period once every four months and then completely recharged. The battery compartments are sealed to prevent gases escaping into the submarine, or salt water entering which inside a battery would cause the release of poisonous chlorine gas. Ventilation fans are used to extract hydrogen released by the cells and catalytic converters are placed strategically through the submarine which remove hydrogen from the air by recombining it with oxygen to form water.

Each of the two propellers on the submarine is connected to a 3000 BHP DC electric motor. Each motor is designed with two separate armatures, in effect two motors in the same unit. Speed of the submarine can be varied by connecting the batteries and armatures in different series and parallel combinations. Slowest speed is obtained by connecting both batteries in parallel, thus supplying 440V, across all four motor armatures in series, thus applying 110V to each ('shafts in series'). Next, the batteries in parallel may be applied across the two motors in parallel, with their armatures in series ('group down'). This applies 220V across each armature. Third, both batteries are applied in parallel across all four armatures applying 440V to each ('group up'). Finally, the batteries can be arranged in series so as to apply 880V across all four armatures in parallel ('batteries in series'). 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 Amps).

The motors are designed with a sealed oil sump from which oil is pumped continuously to lubricate the bearings. A fan draws air from the engine room through the motor to cool it and returns the exhaust air to the engine room through a water cooled heat exchanger. This arrangement reduces the possibility of water being drawn into the motor should there be a leak in the cooler. The engine is also fitted with a heater to keep it warm when not running so as to prevent condensation internally. Temperature and revolution speed are monitored and displayed on the control panel.

Auxilliary power
The batteries provide variable DC power (VP) which ranges in normal usage from 390 to 650 Volts. Pumps for ballast, water, air compressors, ventilation, cooling and hydraulics are all designed to cope with this supply range but some equipment cannot. The boat therefore is supplied with two sets of auxiliary motor generators designed to be powered by the batteries and produce stable output, one set powered by each main battery. A 220V DC supply (CP) is provide by two 100 kW generators, one supplied from each battery with either being sufficient by itself. Two 15 kW 60 Hz three phase alternators provide power for equipment designed to work off 115 or 230V AC and two more 15 kW 400 Hz generators provide power at 205V AC used by radar, sonar, fire control and communications electronics. Two 4 kW generators plus an additional backup battery provide 24V DC.

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.

Regional variations

 * Australia
 * The Royal Australia Navy acquired six Oberons: an initial order of four and a second order of two. The second order was originally for four submarines, but two were cancelled in favour of expanding the RAN Fleet Air Arm.
 * Australian Oberons had different electronic equipment, using primarily American radar and sonar systems. They had Sperry Micropuffs passive ranging sonar and Krupp CSU3-41 attack sonar. Instead of the British Tigerfish torpedoes, the Australians used American Mark 48 torpedoes. They had a slightly larger payload, carrying 22 torpedoes for the forward tubes, six of which were pre-loaded. Shortly after entering service, the aft torpedo tubes in all six submarines were sealed.
 * The Australian submarines were later updated to be equipped with the subsonic anti-ship Harpoon missile. In 1985, off the island of Kauai in Hawaii, HMAS Ovens became only the second conventional submarine in the world—and the first Oberon—to fire a sub-surface-launched Harpoon missile, successfully hitting the target over the horizon. Consequently, the designation for the Australian Oberons changed from SS to SSG.


 * Brazil
 * The main differences between the Brazilian and British Oberons was the fire control systems used; with a Vickers system used. The three Brazilian submarines were later upgraded to use the more advanced Mod 1 Tigerfish torpedo.


 * Canada
 * The three Canadian submarines were built with improved air-conditioning systems, while as many common components as possible were replaced with Canadian equivalents. The Canadian Oberons used United States Navy torpedoes throughout their career: they were initially equipped with Mark 37 torpedo, but were later upgraded for Mark 48 torpedoes.


 * Chile
 * Chilean submarines were identical to their British counterparts except for carrying German SUT torpedoes.

Service
The first of the class to be commissioned into the Royal Navy was Orpheus in 1960, followed by the name vessel 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 (S21) took part in the Falklands War, the only conventional submarine of the RN to do so, landing members of the SBS. All Oberons in service, including boats exported, have now been decommissioned; the last RN boats were decommissioned in 1993, with the final Canadian and Australian Oberons decommissioned in 2000.

Like the 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 North Atlantic; and the Australians throughout south-east Asia and as far north as the Sea of Japan.

The Oberon class was 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.

Fates
As of 2006, at least fourteen Oberons are confirmed to have survived in some form. Seven have been preserved and converted into museum vessels or tourist attractions. Two have been partially preserved as monuments, while another five are awaiting conversion for museum work, or are otherwise awaiting disposal.

Two of the ex-Royal Navy submarines have been preserved in the UK. HMS Onyx has now moved to Barrow-in-Furness after the museum at Birkenhead, Merseyside closed, where another Falklands veteran, the frigate HMS Plymouth (F126), has remained. The other boat, HMS Ocelot (S17), is located at Chatham. HMS Otus (S18) is harboured in Sassnitz, Germany on the island of Rügen and can be visited. Another two British Oberons were transferred to Canada: HMS Olympus (S12) as a non-commissioned training vessel, and HMS Osiris (S13) for spare parts. The other British submarines were disposed of.

Australia's six Oberons have been preserved and are on display, either completely or partially. HMAS Ovens is located at the Western Australian Maritime Museum at Fremantle, while HMAS Onslow is located at the Australian National Maritime Museum in Darling Harbour, Sydney. The fin, outer hull, and stern section of HMAS Otway (S 59) are preserved on land at Holbrook, New South Wales. HMAS Otama is located at Westernport Bay, Victoria, where she has been awaiting conversion into a museum vessel since 2000; a lack of funding and cooperation 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. HMAS Oxley (S 57)'s fin stands as a permanent memorial at HMAS Stirling, Garden Island, Western Australia. HMAS Orion's fin stands as a permanent memorial at Rockingham Naval Memorial Park in Western Australia.

In 2005, it was announced that the four surviving Canadian submarines (minus Osiris, which was scrapped in 1992 after being stripped for parts) were to be sold for scrapping, as they had deteriorated beyond the point of use. HMCS Onondaga (S73) was purchased for C$4 plus tax by the Site historique maritime de la Pointe-au-Père for use as a museum vessel, and was towed from Halifax to Pointe-au-Père, Quebec in July 2008. In July 2011, Olympus was towed to a scrapyard in Port Maitland, Ontario, with HMCS Okanagan (S74) to be delivered to the same scrapyard in August 2011. HMCS Ojibwa (S72) has been preserved as part of the Elgin Military Museum. She was moved to Port Burwell, Ontario in November 2012, and will become a focal point of a new Museum of Naval History. Ojibwa will be open for tours in mid-2013.

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. The surviving Brazilian Oberon, Riachuelo, was converted into a museum at the Brazilian Navy Cultural Center (Espaço Cultural da Marinha Brasileira) in Rio de Janeiro.

The Chilean Navy sold O'Brien to the city of Valdivia, to be converted into the first submarine museum of Chile. The submarine is to be modified in Asenav shipyard with better access for general public and to be moored in the Calle-Calle river that cross the city.

Successors
The Oberon class was briefly succeeded in RN service by the Upholder-class submarine. The Upholder-class submarines were later upgraded and sold to the Canadian Forces after refit as the Victoria class, again replacing Oberons.

The Australian Oberons were replaced by the six Collins-class submarines.

The two Chilean Oberons were replaced by the Scorpène-class submarines O'Higgins and Carrera.

The Brazilian Oberons were replaced by ''Type 209 submarines.