Refuelling the Ambition: SDSR 2015’s Combat Air Oversight

Despite a slew of high-end capabilities announced by the SDSR in the combat air domain, fuelling these new aircraft might prove a more subtle difficulty

Given the prior expectations, the 2015 SDSR has been a good one for the armed services. However, most would agree that the RAF in particular has done particularly well with the announcement of two more Typhoon squadrons (although without any extra aircraft), nine P-8 Poseidon anti-submarine warfare and maritime surveillance aircraft, an extension of the Sentinel force, and a commitment to all 138 of the F-35 Lightning IIs originally envisaged when Britain joined the programme. Whilst there will undoubtedly be difficulties encountered in funding and training sufficient manpower to crew these assets effectively within a still constrained budget, the RAF (and the Royal Navy’s Fleet Air Arm) now have a solid equipment plan to enable high-end warfighting until 2030 and beyond.

But there is one problem with both big-ticket purchases.

Beyond the two and possibly eventually three squadrons of F-35B short-takeoff, vertical landing (STOVL) aircraft for the joint RAF/Royal Navy force which will operate from the Queen Elizabeth-class carriers and land bases, the remaining 80–90 F-35s in the order will almost certainly be conventional take-off and landing F-35As for the RAF. The F-35A is the version which the USAF will acquire in large numbers and also the version favoured by most international customers. It is, therefore, the least technologically risky option and also happens to be the cheapest in terms of unit and operating costs by a considerable margin. The F-35A will probably be purchased from the early to mid-2020s and will initially complement and later slowly begin to replace Typhoon as the latter is drawn down through the 2030s towards its out-of-service date in 2040.

However, unlike all current RAF combat aircraft, the F-35A cannot refuel using the probe and drogue system on the RAF’s Voyager KC-2 and KC-3 tanker aircraft, being configured for the USAF’s flying-boom-equipped tankers. The P-8, which is based on a modified 737 commercial airliner, also can only refuel using the USAF’s flying-boom system. Although the RAF’s new RC-135 Airseeker electronic intelligence aircraft has the same limitation, because it is operated alongside the USAF’s fleet of RC-135 Rivet Joint aircraft with rotating crews from both nations as part of a de facto common fleet, this is less of an issue since the Airseeker can almost always rely on access to American boom-equipped KC-135 or KC-10 tankers.

Extending the P-8’s range and endurance on station during long maritime surveillance and anti-submarine patrols, especially if carry drag-inducing external stores, will require regular access to aerial refuelling. This is especially important given that the UK plans to order only nine of the expensive aircraft. If the fleet is required to conduct any overseas deployments then there will be very few aircraft available to maintain a twenty-four hour search pattern over UK waters if required. A suspected Russian submarine presence in UK waters, a threat to the Vanguard-class strategic missile submarines on nuclear deterrent patrol or a search-and-rescue mission for a crashed aircraft or sunken ship could all required a non-stop P-8 presence on station at very short notice without warning. Extending the time available for each aircraft on station over potentially distant areas of interest will be critical in such a situation and the UK cannot rely on dedicated USAF tanker support being available to support such operations at short notice.

The F-35A will be even more heavily dependent on tanker support than the P-8 fleet because as a tactical fighter without provision for external fuel tanks it will have very short endurance on internal fuel. This will be exacerbated by the relatively high-drag, high-thrust and -weight nature of the airframe design, although internal weapons carriage in high-threat scenarios does mitigate the drag somewhat by eliminating penalties from external weapons stores. However, if flying on internal fuel with external stores, the F-35 will be particularly limited in terms of endurance and, therefore, combat radius. External fuel tanks were originally intended for development with the F-35 but their design and testing is currently not part of the funded programme. It is worth noting that the majority of RAF sorties with Typhoon carry few external weapons stores, carry two external fuel tanks and still need to refuel at least once per flight. When conducting operations over Libya in 2011, RAF Typhoons and Tornados were refuelling up to six times per sortie.

If the RAF has to rely on USAF tanker support for any F-35A operations, any notion of sovereign mission planning and execution capability would be wishful thinking: without the capability to refuel from RAF tankers, British F-35As would be completely tied to American strike packages for fuel. They would also represent a further burden on the USAF’s already overstretched tanker fleet.

It is clear, therefore, that if the P-8 and F-35A are to form a significant and useful part of British combat air power, then the A-330 MRTT Voyager fleet will have to be modified to include an aerial refuelling boom system. Luckily, the Voyager was designed to incorporate both the probe and drogue underwing refuelling pod system and a centreline aerial refuelling boom. Australia, the United Arab Emirates and Saudi Arabia already operate the aircraft in this configuration. Unfortunately, the UK specifically opted for a probe and drogue-only configuration for its KC2 and KC3 variants. Given that refitting the interior of one of the RAF’s fourteen Voyagers to enable it to carry VIPs is reportedly going to cost £10 million, modifying some or all of fleet with a boom which would amount to a major internal plumbing and airframe modification will most likely run into the hundreds of millions of pounds. This will not be the only investment required, as the refuelling boom is ‘flown’ from inside the tanker by an operator, as opposed to the probe-and-drogue baskets which trail behind the tanker and rely on the receiving aircraft’s pilot to manoeuvre into position. This means that a boom-equipped Voyager force would need to train and maintain currency for boom operators – something the RAF has no recent institutional experience in.

These challenges are by no means insurmountable, but will undoubtedly be expensive and require more manpower from a service and budgets which have little headroom for more manpower and equipment costs. It is an example of an oversight in an SDSR dominated by big-ticked equipment purchases and light on detail about how these purchases will be incorporated into a UK military in the midst of restructuring and hard-pressed for capacity and manpower.

Justin Bronk
Research Analyst in the Military Sciences research group at RUSI.


Justin Bronk

Research Fellow, Airpower & Technology

Military Sciences

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