Development of the Queen Elizabeth class aircraft carrier – a design history
In this article, we review how the design of the Queen Elizabeth Class (QEC) aircraft carriers evolved. This is a broad subject, worthy of several books but this article provides an overview.
Given their size and limitations, the three Invincible class carriers (CVS) had served the nation very well but by the late 1990s consideration of how to replace them was being discussed. In 1997 the MoD began some outline concept studies for potential future carriers. At this stage, it was accepted they would be considerably bigger than the CVS and most likely operate VSTOL aircraft, although a conventional carrier operating Boeing F/A-18E Super Hornet or even a navalised ‘Sea Typhoon’ were briefly considered. Operational analysis suggested that 50 aircraft would be needed to ensure campaign success in medium-intensity scenarios and would probably require a ship displacing at least 38,000 tonnes. Probably for the benefit of the Treasury, the MoD did, however, examine life extension refits and hull-stretching the CVS but unsurprisingly in 1999 concluded that the hulls were too old and lacked the beam to comfortably operate larger future aircraft (the JSF eventually grew to twice the size of the Harrier).
The decisions of the 1998 Defence Review were generally sound and promised the navy would have “two 40,000 ton aircraft carriers, with a complement of up to 50 aircraft and helicopters each. The first will have an in-service date of 2012”. The Future Aircraft Carrier project to build the CVF was formally launched in January 1999. In the light of the capabilities forecast for the QEC by the mid-2020s it is interesting to reflect on how closely they will fulfil the 9 original Key User Requirements (KUR) that were laid down in 1999.
- Interoperability – able to contribute to joint and international operations
- Integration – able to integrate with the joint battlespace and support air group operations with command, control, communications and intelligence functions
- Availability – able to provide one operational ship available at all times
- Deployability – able to deploy worldwide
- Sustainability – able to mount sustained operations
- Aircraft – able to deploy offensive air power without host-nation support
- Survivability – have a high probability of surviving damage
- Flexibility – able to operate the largest possible range of aircraft
- Versatility- able to operate in the widest range of roles.
The assessment phase began at the end of 1999 with initial £5.9M Analysis of Options contracts awarded to two consortia lead by British Aerospace (now BAE Systems) and Thomson-CSF (now Thales). This was followed by the award of a second year-long £30M assessment phase contract to both teams in July 2001.
There was considerable scope for creativity and innovation and the only major stipulations beyond the KURs were that the ship must be built in Britain, carry up to 48 aircraft, be single-hulled and not nuclear powered. Affordability was obviously a major consideration and through-life costs were to be given very high priority. Because the crew is such a major factor in the cost of ownership, a target ships company of around 600 was suggested by the MoD. Both consortia gave this considerable attention and the resulting low manpower requirement is a major achievement.
Three possible configurations were to be examined; conventional catapult-assisted take-off, barrier assisted landing (CATOBAR colloquially referred to as ‘cats and traps’), Short take off, barrier assisted landing (STOBAR) and short take-off, vertical landing (STOVL) options. A fourth option of a ‘hybrid’ CATOBAR and STOVL carrier was briefly considered during 2000 but quickly eliminated as too expensive.CVF-flight-deck-configuaration
By 2001 it was clear the UK would be participating in the JSF (Joint Strike Fighter / F-35) project and the STOBAR option was eliminated. The original specification called for a carrier that could launch 150 fixed-wing sorties every 24-hours, but by late 2002 the figure had been reduced to 110. BAE Systems studies indicated that a CATOBAR carrier would need to be at least 10,000 tonnes larger than a STOVL design.
In September 2002 it was confirmed the design would be an ‘adaptable carrier’ configured with a ski jump for STOVL but capable of being fitted with catapults and arrestor gear if required at some point in the future. The displacement had by now grown to 60,000 tonnes. The First Sea Lord, Admiral Sir Michael Boyce stated that RN studies had decisively concluded that a larger ship is cheaper to build in terms of cost per tonne but also has lower maintenance costs. His maxim “air is free, and steel is cheap” was widely quoted and inline with a global trend for larger combatants. Work done in the 1960s for the cancelled CVA-01 carrier design found that increasing tonnage from 40,000 to 50,000 tons increased costs 10%, but aviation capability by 50%. Conversely, the CVF designers concluded in 2001 that a 25% cost reduction for both ships, from £4 billion to £3 billion, would result in a 50% cut in sortie rate. A larger ship also met the criteria for sortie generation, adaptability, comfortable accommodation standards and the ability to embark extra personnel and aircraft in an emergency. The bigger ship is also easier to upgrade in future, a major consideration for a vessel with a planned lifespan of 50 years.
A major factor in any aircraft carrier design is the size and layout of the hangar. With the JSF project not yet mature, the initial design assumed a capacity of 26 aircraft with an approximate wingspan of 12m. (The F-35B does not have folding wings and has a maximum wingspan of 10.7m) The beam of the ship is critical for seakeeping and stability, constraining the size of the hangar. The adaptable carrier also requires a gallery deck immediately below the flight deck and above the hangar, where catapults and arrestor gear could be fitted. The Hangar must interface with the aircraft and weapons lifts in a way that is optimal for aircraft movements. To maximise protection, weapon magazines are located deep in the centre of the ship and together with their associated lifts, are one of the first items that needed to be fixed in the design. The large size of CVF allowed the selection of deck-edge lifts which would be vulnerable to heavy seas if used in small carriers. Deck-edge lifts have several advantages, including a larger capacity than internal lifts.
Alpha – Delta
In December 2002 the Thales / BMT Alpha concept was selected by the Integrated Project Team (IPT) as the preferred design, beating the proposal from BAE Systems who had been expected to win. The Alpha was seen as more innovative and technically developed than the BAES design. The Alpha employed a simpler main hull shape with large sponsons for a very wide (70m) flight deck. It was less stealthy than the flared hull form of the BAES proposal but this was not a key requirement for CVF.
The twin island design offered many advantages The BAES design featured 3 small aircraft lifts with one emerging oddly in the centre of the novel island structure. It was also fitted with four Sea RAM ILMS defence systems located on each quarter. The Alpha had two large aircraft lifts, a larger hangar and podded propulsion which was seen as an innovation from cruise ships that could be exploited by CVF. The Alpha also had VLS cells for Aster missiles, 3,000 tonnes of armour protection and very high survivability standards.CVF-iterations-5
Unfortunately, by mid-2003 it was clear the Alpha was an unaffordable gold-standard option. A scaled-down, stripped-back, ‘minimum viable technical design’ was then produced, the 55,000-tonne Bravo. The podded propulsion was deleted as by now it was accepted they could not meet naval shock resistance and noise signature standards. The Alpha’s fully automated weapon handling system was replaced with a cheaper and semi-manual highly automated system and self-defence measures were pared back to soft-kill only and ‘fitted for, but not with’ close-in weapons.
Although supposedly saving around £200m in construction costs, it was quickly established by the Defence Procurement Agency Sea Technology Group (STG) that the Bravo did not meet damage control and stability standards. The Charlie variant was then developed with greater subdivision but this reduced internal volume further. The compromises of the Bravo and Charlie were seen to be adding technical risk and complications to construction and the RN successfully argued for a small increase in budget for a slightly larger ship. The result was the 65,000 tonne Delta which was subsequently adopted as the basis for the QEC we know today.
The third assessment phase saw newly formed Carrier Alliance working on refinements but the project now entered a politically turbulent period of delay, indecision and attempts to control costs. In December 2005, funding for the demonstration phase – the detailed design was approved.
In 2005 BMT announced it has tested 4 different CVF hull form models and assessed them for propulsion efficiency, manoeuvrability, seakeeping and noise signatures. It also investigated skeg length, rudder size, transom stern flaps and bulbous bow designs. The basic Delta concept went through many further iterations and development before the design was considered sufficiently mature by late 2006 for detailed cost estimates to be drawn up prior to ordering long-lead items. Complex funding and industry arguments held up progress considerably but Queen Elizabeth class ships were finally ordered on 25 July 2007 (Although there were further politically-inspired delays after this point).
The ship would be a hybrid of the new Lloyds Naval Ship Rules, maximising use of commercial off-the-shelf (COTS) equipment where possible, while built to defence standards in many critical areas. The CVF design principles were, however, very different to the cheaply-built HMS Ocean, having much higher survivability standards and avoiding over-reliance on commercial equipment that did not stand up well to the rigours of naval service.
The QEC have a large, 16,000m2 flight deck in a flexible layout optimised for best aircraft traffic flow with a single runway and ski ramp. The 4,727m2 (29,000 metre3) hangar has a maximum capacity of about 20 x F-35s or a larger number of helicopters. Without the need for catapults, the QEC can utilise the large gallery deck for aviation offices, aviation stores and an aircrew refreshment bar. Selecting a large ship offers a generous allowance for weight growth margins of up to 16% for additional equipment to be added through the planned 50-year life of the ship. If cats and traps were ever fitted it could add significantly to the displacement, much of the weight would be ballast in the bottom of the ship to counteract the added topweight.
The ship has Integrated Electric Propulsion (IEP), four electric motors drive twin shafts in a conventional arrangement. Two gas turbines and 4 diesels provide the power for propulsion, electronics and the hotel load with a large extra margin of power available for future requirements. Automation has been used wherever possible, especially for weapons and stores handling to reduce manning needs. Modern waste disposal equipment is fitted to make the ship as environmentally friendly as possible. (More details of the QEC design can be found in various related articles here)CVF-2009
The development of such large and complex vessels was never likely to be entirely straightforward but most of the hindrances have been more political than technical. Only after a few years of active service can the ship’s success be fully judged but early indications are good. HMS Queen Elizabeth, effectively a prototype vessel, passed initial sea trails with no major problems (Although perhaps she was lucky to avert a total failure of the propeller shaft thrust block). Despite the many obstacles and external pressures that shaped the project, the designers succeeded in creating a highly innovative aircraft carrier that has a potential for further development. A very good balance has been struck between compromises on capability, initial costs and through-life costs. In a future article, we will look at the delays, the cats and traps detour, passing French involvement and the political background.