Editing Oberon-class submarine (section)

==Design and construction==
The {{convert|295.2|ft|m|adj=on}}-long ''Oberon'' class was based on the preceding [[British Porpoise-class submarine|''Porpoise'' class]] of submarines, which were in service from 1956 to 1988.<ref name=compedium/> Changes from the ''Porpoise'' design were primarily to improve the strength and stealth of the submarine.<ref name=compedium/> Instead of UXW steel, the hull was built from QT28 steel, which was easier to fabricate and stronger, allowing the submarine to dive deeper.<ref name="brown&moore">Brown & Moore, ''Rebuilding the Royal Navy'', p. 116</ref> [[Glass-reinforced plastic]] was used in construction of the [[casing (submarine)|casing]].

[[File:HMAS Onslow fin and masts.jpg|left|thumb|The fin and equipment masts of {{HMAS|Onslow}}]]
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.<ref name=compedium/> The ''Oberon''s 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]].<ref name=compedium/> Construction of the British submarines was shared amongst four dockyards: the three mentioned above and [[Cammell Laird]].<ref name=compedium/>

===Armament===
{{More citations needed section|date=June 2015}}
[[File:Attack Periscope Type CH74 - RAN Oberon Class Submarine 1957-99.jpg|left|thumb|upright|[[Barr and Stroud]] Attack Periscope Type CH74 – RAN ''Oberon''-class submarine]]

[[File:Fire Control Consoles - HMCS Onondaga.jpg|left|thumb|Torpedo fire control consoles aboard HMCS ''Onondaga'']]

The ''Oberon''s were originally armed with eight {{convert|21|in|mm|1|adj=on}} torpedo tubes: six tubes in the bow, and two short tubes for antisubmarine defence in the stern.<ref name=compedium/> The submarine normally carried a payload of 20 torpedoes for the forward tubes; a mix of [[Mark 24 Tigerfish]] and [[List of torpedoes#21" Mark VIII|Mark 8]] torpedoes, while only the two preloaded [[British 21 inch torpedo#21 inch Mark 20 Bidder|Mark 20S]] torpedoes were carried for the stern tubes.<ref name=compedium/> [[Naval mine]]s could be carried instead of torpedoes: the torpedo payload would be replaced with up to 50 [[Stonefish (mine)|Mark 5 Stonefish]] or Mark 6 Sea Urchin mines.<ref name=compedium/>

The forward torpedo tubes are constructed in two sections bolted together across the bulkhead at the fore end of the torpedo compartment. The {{convert|116|in|cm|adj=on}} long inner section is constructed of {{convert|0.5|in|cm|adj=on}} rolled steel fitted with welded flanges and support brackets.  The outer section is constructed of a similar tube {{convert|175|in|cm}} long but with a reinforced {{convert|1.125|in|cm|adj=on}} 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.

[[File:Ocelot-TorpedoTubes.JPG|right|thumb|Forward torpedo tubes on {{HMS|Ocelot|S17|6}}]]
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 be fired either electrically or with compressed air.{{Citation needed|date=February 2024}}

The aft torpedo tubes passed through the ballast tank at the rear of the submarine. A {{convert|31|in|cm|adj=on}} section projected into the boat through the bulkhead, forming overall a relatively short tube of {{convert|12|ft|m}}, but of {{convert|25|in|adj=on}} diameter.

With the retirement of the Mark 20S torpedo in the 1980s, the stern torpedo tubes were decommissioned and the torpedo ballast tanks were thereafter used for storing beer.<ref>{{cite book|title=The Encyclopedia of World Sea Power|page=[https://archive.org/details/encyclopediaofwo0000unse_v9e5/page/42 42]|author=Chris Bishop and Tony Cullen|publisher=Crescent Books|year=1988|isbn=0517653427|url=https://archive.org/details/encyclopediaofwo0000unse_v9e5/page/42}}</ref>

===Propulsion systems===
The class used [[diesel-electric]] propulsion, with [[Lead-acid battery|lead-acid batteries]] to provide power when the engines cannot be used. Each vessel has two Admiralty-pattern V-16 [[diesel engine]]s (ASR1 16VMS), each driving one 1280-kW 880-V [[Electric generator|generator]]. These can provide power directly to the two {{convert|3000|bhp|lk=in|adj=on}} [[electric motor]]s, one directly connected to each [[propeller]], 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 [[Submarine snorkel|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 the fresh air spreads through the boat.<ref name=SFMNPA>{{cite web |title=C.F. 'O' Class Submarines - Electrical Systems |url=https://maritime.org/doc/oberon/electrical/index.php#toc |website=San Francisco Maritime Nation Park Association |access-date=10 June 2024}}</ref>

[[File:HMS Otus - Sassnitz - inside 10.jpg|thumb|right|Engine compartment on {{HMS|Otus|S18|6}}, twin V16 diesel engines]]
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. A grill allows 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 440&nbsp;V 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 it can be split into two banks of 112 cells.  The cells are designed to deliver 7420&nbsp;[[Ampere hour|Ah]] at the five hour discharge rate. 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 {{convert|1,120|lb|abbr=on}} and contains 18.5&nbsp;gallons of electrolyte. Cells are held tightly 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.<ref name=SFMNPA />

In operation, each battery is charged until the voltage reaches 560&nbsp;V, then allowed a further hour's charging. Fortnightly, it should be allowed 5 hours' charging after reaching 560&nbsp;V to ensure a maximum charge is reached. Every two months, the battery should be given an equalising 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 1.080 and 1.280. Initial charging current should be around 1650&nbsp;amps for s.g. below 1.180, 1250&nbsp;A above 1.180, falling to 280&nbsp;A when charging is complete. At a voltage around 538&nbsp;V, 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 280&nbsp;A, which is then maintained while voltage is allowed to rise until  the requisite voltage and charge time are reached. In an emergency, the charging current can be raised to 2000&nbsp;A. To maintain overall capacity, batteries need to be completely discharged over a five-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 to remove hydrogen from the air by recombining it with oxygen to form water.<ref name=SFMNPA />

[[File:HMS Ocelot 1962 propellor motor control panel.JPG|thumb|right|Propeller motor control panel: The panel telegraph (top and left) showed instructions issued from the motor telegraph position beside the helm station in the control room which were to be carried out.]]
Each of the two propellers on the submarine is connected to a 3000&nbsp;bhp DC electric motor. Each motor is designed with two separate [[Armature (electrical engineering)|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 440 V, across all four motor armatures in series, thus applying 110&nbsp;V 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 220&nbsp;V across each armature. Third, both batteries are applied in parallel across all four armatures applying 440&nbsp;V to each ('group up'). Finally, the batteries can be arranged in series so as to apply 880&nbsp;V 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&nbsp;A).<ref name=SFMNPA />

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 motor 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.<ref name=SFMNPA />

===Auxiliary power===
{{Unsourced section|date=June 2015}}
The batteries provide variable DC power (VP), which ranges in normal usage from 390 to 650 V. 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 220 V DC supply (CP) is provided by two {{convert|100|kW|abbr=on}} generators, one supplied from each battery with either being sufficient by itself. Two {{convert|15|kW|abbr=on}} 60&nbsp;Hz three-phase alternators provide power for equipment designed to work off 115 or 230 V AC and two more 15&nbsp;kW 400&nbsp;Hz generators provide power at 205 V AC used by radar, sonar, fire control, and communications electronics. Two {{convert|4|kW|abbr=on}} generators plus an additional backup battery provide 24 V 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.<ref name=SFMNPA />

===Regional variations===
[[File:HMAS Oxley bow back.jpg|thumb|left|upright|The preserved bow section of {{HMAS|Oxley|S 57|6}}: The mouths of the six torpedo tubes are displayed, along with the modified sonar dome and a mockup of the bow sonar array.]]
;Australia
:The [[Royal Australian Navy]] acquired six ''Oberon''s: 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 (RAN)|Fleet Air Arm]].<ref name=Stevens194>Stevens (ed.), ''The Royal Australian Navy'', p. 194.</ref>
:Australian ''Oberon''s had different electronic equipment, using primarily American sonar systems. They had [[Sperry Corporation|Sperry]] [[BQG-4]] Micropuffs passive ranging sonar and [[Krupp]] CSU3-41 attack sonar.<ref name=compedium/> Instead of the British Tigerfish torpedoes, the Australians used American [[Mark 48 torpedo]]es.<ref name=compedium/> They had a slightly larger payload, carrying 22 torpedoes for the forward tubes, six of which were preloaded. 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 antiship [[Boeing Harpoon|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 subsurface-launched Harpoon missile, successfully hitting the target over the horizon. Consequently, the designation for the Australian ''Oberon''s changed from SS to SSG.

;Brazil
:The main differences between the Brazilian and British ''Oberon''s was the fire-control systems, with a Vickers system being fitted to the Brazilian boats.<ref name=compedium/> The three Brazilian submarines were later upgraded to use the more advanced Mod 1 Tigerfish torpedo.<ref name=compedium/>

;Canada
:The three Canadian submarines were built with improved air-conditioning systems, while as many common components as possible were replaced with Canadian equivalents.<ref name=compedium/> The Canadian ''Oberon''s used United States Navy torpedoes throughout their career: they were initially equipped with [[Mark 37 torpedo]]es, but were later upgraded for the [[Mark 48 torpedo|Mark 48s]].<ref name=compedium/>

;Chile
:Chilean submarines were identical to their British counterparts except for carrying German [[SUT torpedo]]es.<ref name=compedium/>