Author Topic: HMS Cumberland - Britain's first nuclear warship  (Read 3280 times)

Offline Weaver

  • Skyhawk stealer and violator of Panthers, with designs on a Cougar and a Tiger too
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HMS Cumberland - Britain's first nuclear warship
« on: November 03, 2015, 09:01:09 PM »
HMS Cumberland - Britain's first nuclear warship.


Following the successful development of a reasonably compact and navalised nuclear reactor at the Dounreay research establishment in the late 1950s, Britain's first nuclear warship, the guided missile cruiser HMS Cumberland, was laid down in 1960, and commissioned in 1963. The design of the ship differed in a number of ways from the first ever nuclear warship, the USS Long Beach. The US Navy had boldly opted for an all-nuclear power plant, but the Royal Navy decided to be more conservative, so Cumberland had a CONAS (Combined Nuclear And Steam) system, a single reactor being paired with a conventional steam plant of the same design as used in the County class destroyers being produced at the same time. The uptakes for the boilers were lead into a "mack" (combined mast and stack: a first for the Royal Navy) in order to make best use of the centreline space freed up by the lack of funnels. Another difference was the adoption of electric, rather than mechanical drive, this being chosen in order to minimise the amount of steam piping in the ship and allow the reactor to be completely isolated should it have a problem.

The comparison with the County class destroyers was important, since one of the principal roles of the new ship was to evaluate nuclear versus conventional propulsion, together with a range of other tactical and technical concepts. To this end, the ship was equipped with all the same systems as a County, but given the ship's size (more than twice the displacement of a County) she was given more or larger versions of many of them, one of the arguments of the the nuclear proponents being that the increased size and cost of nuclear ships was compensated for by their increased fighting ability. Partly to reflect this, the ship was rated as a cruiser, and given the pennant number of the previous HMS Cumberland which had been scrapped in 1958, having spent the latter part of her career, appropriately enough, as a trials ship.

As first commissioned, Cumberland had two twin 4.5" Mk.6 gun turrets in A and B positions, and a Limbo ASW mortar in a deckhouse in C position. Aft, a triple Seaslug SAM launcher and it's enormous magazine dominated the design. Cumberland's size meant that she could carry two Type 901 fire control radars for this system, so the increased beam was used to carry two hangars for Wessex ASW helicopters on either side of the radars. A pair of Seacat short-range SAM systems sat on the hangar roofs, and the final layer of defence was provided by two 20mm Oerlikon guns just behind the bridge. By contrast, the Counties had a twin Seaslug launcher with only one type 901, a single Wessex housed in a very cramped and awkward hangar and no Limbo mortar. Cumberland also carried the same enormous Type 984 3D radar as was being fitted to some, but not all, of the Royal Navy's carriers at the time, the intention being to analyse whether this unit was more effective when fitted to a carrier or one of it's escorts.



Cumberland as first commisioned. The 'empty' area amidships was for reactor access. The Limbo mortar was concealed within the deck house immediately ahead of the bridge.


HMS Cumberland spent much of the 1960s involved in trials and exercises designed to prove the safety and utility of nuclear power and was judged to be very successful in this role. However some of her technology (notably the Seaslug missile system) was regarded as dated even before she commissioned and since the various trials had confirmed the reliability and safety of nuclear power at sea, it was decided that the next class of cruisers would be built to a very different design, with all-nuclear propulsion and the much more compact and capable Sea Dart missile system. The new ships' power plants would not be British however. The Americans had convinced the UK and NATO governments of the economies of scale to be had from mass production of their D2G design, so the new Royal Navy cruisers would be based around two of these plants leaving the British surface ship reactor programme to devote all it's resources to development of the plants for the new CVAN-01 carriers, for which no appropriate US system existed. HMS Cumberland thus remained the sole example of her type.

That left the question of what to do with Cumberland. With the trials phase of her life largely over, she was refitted for fleet duties in the 1970s along the same lines as the second batch of Counties, with improved radar and fire control systems, Exocet missiles in place of the Limbo mortar, and STWS-1 torpedo tubes. Unlike the Counties however, the enormous cost of the ship made it unacceptable to government and public alike that she should be paid off early, and so, despite the obsolescence of her main weapon system, she soldiered on into the 1980s. She deployed to several trouble spots during this period, including Cyprus, the Falkland Islands and Lebanon, but of course, never fired her weapons in anger.


Cumberland as she appeared following her 1970s refit. Note the AKE-2 aerial for the Type 965 radar and the Exocet launchers on the former Limbo deck house.


When the last County was sold off the Seaslug system became impossible to support and the issue of retiring Cumberland arose again. In truth, the RN would have quite liked to retire her at this point and put the manpower to other use, but again, public opinion and government policy forbade it so another use had to be found for her. After much debate, she was refitted as a command and ASW cruiser. The Knot defence review of 1980 had cancelled plans for a third nuclear carrier and it's escorting helicopter cruiser so the argument was that refitting Cumberland would get more Sea Kings into the fleet. Sea Slug was removed and replaced with an extended flight deck, and the old Type 901 radars and hangars were replaced by an enlarged hanger for three Sea King helicopters (though she rarely operated more than two in practice). Air defence came from Sea Wolf point-defence missile launchers fitted on the hangar roof and in place of B turret, while two Vulcan Phalanx radar-directed gatling guns were fitted amidships. Radars and electronics were also given a comprehensive update.

At the time it was claimed by some commentators (and swiftly thereafter by some newspapers) that this refit was ill-conceived and half-hearted, with critics pointing to the retention of Exocet (when new-builds had moved onto Harpoon), the elderly 4.5 Mk.6 gun turret and the original sonar, and the failure to fit a towed array. In response, the RN countered that updated sonar and a towed array were rejected because the nuclear plant was inherently noisy, the ship's Sea Kings could provide long-range anti-ship fire with Sea Eagle ASMs, and with Sea Wolf and Phalanx providing more than enough air-defence, an updated gun turret would provide little real benefit for it's price.



Cumberland in her final configuration as a helicopter cruiser.


 The original intention was for Cumberland to run on into the 21st century in her new role as a CHN, thus getting the forty years of service that was felt to be acceptable given her cost. However a further refit was cancelled in the early 1990s due to post-Cold War defence spending reductions, and cracks were then found in her reactor's primary cooling circuit which would be very expensive to repair, so she was swiftly taken out of service in 1996 and unceremoniously scrapped. However even at the end of her life HMS Cumberland continued to serve, since she was was the first British nuclear warship to be decommissioned and many important lessons were learnt in the process.


The profiles were modified from County class Shipbucket profiles by 'Hood', who does lovely work. Note however that mine are not fully to Shipbucket standards because I've compressed the layout to get best reproduction after posting them on the forum via Photobucket. Various minor elements were taken from other profiles and resources on www.shipbucket.com which is a very excellent place for whiffers and real-world ship geeks alike.
« Last Edit: November 03, 2015, 09:06:36 PM by Weaver »
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Offline Volkodav

  • Counts rivits with his abacus...
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Re: HMS Cumberland - Britain's first nuclear warship
« Reply #1 on: November 03, 2015, 09:16:02 PM »
Fantastic job Weaver, love it!