Restoring the UK’s maritime patrol aircraft capability (Part 1)

The axing of the troubled Nimrod MRA4 project in 2010 SDSR has left Britain unable to properly patrol its waters and left a serious gap in anti-submarine capability. In 2015 the government tacitly admitted its mistake and announced the plan to purchase nine Poseidon P-8A Maritime Patrol Aircraft (MPA) from Boeing in the United States. In the first part of this article we will look at the programme and infrastructure behind its introduction into service, and the aircraft itself.


Although the US Navy operates its own aircraft, by a historical anomaly the RAF have always owned the UK MPAs – a critical naval capability. This arrangement will continue as only the RAF has the facilities and experienced personnel needed to support the next generation. Since the 1950s, the RAF operated the Shackleton and then the Nimrod MR1 and MR2 maritime patrol aircraft which were largely successful in this role. The planned successor to the Nimrod MR2 was another Nimrod, the MRA4. The tale of woe that led to the eventual cancellation of the MRA4 is long, complicated and depressing and has been discussed in much detail elsewhere. In broad terms the decision to build a ‘new’ aircraft utilising existing ancient Nimrod airframes was disastrous. This and many other factors, meant that by 2010 the project was £789 million over-budget and over nine years late. It should be noted that a production aircraft was flying in 2009 and the first aircraft had been delivered to the RAF. Although there were still serious flaws, it was not perhaps as unsafe or hopeless as government claimed at the time. Anyway, the MRA4 was cancelled and the airframes were chopped into pieces with extraordinary haste, effectively throwing away the £4Bn already spent on the project.

Even by normal dismal defence procurement standards, this government, MoD, BAE Systems and RAF collective failure was a scandal of spectacular proportions.

Enter Posiedon

The P-8A Poseidon has been in development since 2004 intended to replace the venerable turboprop Orion P-3. The P-8 airframe has little in common with the Nimrod or the P-3, being based on a modern, and extremely successful commercial airliner, the Boeing 737-800. On 25 March 2016 the US government approved the sale of nine P-8s to the UK. Although the Japanese P-1 was given cursory consideration, the P-8 was always the strong favourite and is being procured as a direct government sale. Controversially no competition was held and the purchase is not subject to the MoD’s single source regulatory framework. Given the urgency of the situation, this was perhaps sensible. Although expensive, the P-8 is the simply best available option and ease of interoperability with the US Navy is always desirable. The US Navy is buying at least 117 aircraft, Australia 12, India 9 and Norway 5, so the UK will benefit from a multinational development programme and economies of scale.

Having shot itself in the balls with the MRA4 debacle, the UK aerospace industry is in no position to complain about this major foreign purchase. Fortunately, as part of the P-8 deal, Boeing has agreed to expand its UK workforce from 1,300 to 4,000 and is opening a major new aircraft repair and maintenance hub at Boscombe Down. UK industry will also have opportunities to be involved in training and support work for the P-8.

On 11 July 2016, the UK signed a $3.87 billion contract with Boeing for the 9 aircraft and elements of their support which will be delivered in 3 batches. The schedule calls for the first two aircraft to be delivered in 2019, with three more in 2020 and the final four in 2021. It will be at least 12 years after the end of the Nimrod MR2 (which at one time numbered 35 aircraft) before the re-establishment of a ‘full strength’ squadron of 9 P-8s

Regenerating on the front foot

There were those, including some in the RAF, who were not especially enthusiastic about the P-8 and hoped that the focus could be steered away from maritime and instead obtain a more generic ISTAR Multi-Mission Aircraft and/or long range UAVs. However the RAF did have the foresight not to make all its Nimrod aircrew redundant in 2010. The Seedcorn exchange programme has seen around 30 RAF personnel serving aboard US, Canadian, Australian and New Zealand aircraft on 3-4 year tours. UK personnel have already accumulated more than 1,000 hours of flying time on US Navy P-8s and even have won various awards in international anti-submarine warfare competitions. This demonstrates the wealth of skill that the Nimrod force had acquired and will be able to contribute to bringing the P-8 into service. The RAF has also persuaded personnel who previously served on Nimrod to assist with the P-8 introduction. 12 have recently re-joined the RAF and more are set to re-join in the future.

The P-8 will be based at RAF Lossiemouth in North East Scotland. (The Nimrod’s former Scottish base was at RAF Kinloss which has since been converted to an Army base). Despite the ongoing complaints by nationalists about lack of defence investment in Scotland and worries over the future of the Union, the UK government is set to invest further in new support infrastructure including new runways and hangars. Boeing will also set up a P-8 maintenance hub at Lossiemouth and is investing £100M and will create around 100 new jobs. An extra 600 personnel are expected to be stationed at the base by 2020.

Aircraft overview


Main Features of the P-8A. Diagram by kind permission of

Although based on the 737-800ERX, the P-8A is a very different aircraft. The wings are based on the 737-900 but have been substantially re-designed to cope with the stress of more low altitude flying than a commercial jet and to provide four hard-points for weapons. The fuselage has been substantially redesigned with a bomb bay and additional fuel tanks replacing luggage holds. The airframe life will be around 25 years or 25,000 flying hours in tough high and low conditions over the sea and is able to operate in icing conditions or extreme temperatures.

A variety of additional sensors and antenna are mounted externally, all linked to the sophisticated mission systems. It is these sensors and electronics that are the real cost-drivers for an aircraft with a price tag of around £350 Million (Before support and weapons costs are added). The computing and data fusion abilities of the aircraft are what set it apart from other MPAs. The P-8 has the world’s most powerful onboard sonobuoy data processing capability and has space for more sonobuoys than any other MPA. The P-8 was also designed from the outset to be able to control and monitor data from the MQ-4C Triton Broad Area Maritime Surveillance (BAMS) unmanned aerial vehicle. Although a highly desirable force multiplier and rumours about UK Triton orders prior to SDSR 2015, the MoD has no plan or funding in place for such a purchase.

  • Flight deck of the P-8.

  • MPA basics – Port and starboard observer windows allow the sea to be scanned with the “Mark 1 eyeball” (US Navy Photo)

  • Under the hood – AN/APY-10 synthetic aperture radar designed for both coastal and overland surveillance (Image: KeyAero)

  • The retractable MX-20HD electro-optical camera and infrared sensor turret (Image: US Navy)

  • Open bomb bay showing the 5 hard points for torpedos. Also visible forward are the 6 sonobuoy dispenser openings flanked by the Common data link (CDL) attennas. (Photo: Rami Khanna-Prade, via Flickr)

  • Under the APU exhaust is the AN/AAQ-24(V) Directional Infrared Countermeasure (DIRCM) system for protection from heat seeking missiles. (Photo via

  • Removing a Sonobuoy from storage rack ready to be placed in dispenser (US Navy Photo)

  • RAF aircrew at one of the P-8’s five mission workstations – serving with US Navy operating the P-8 under the ‘Seedcorn’ initiative to keep UK MPA skills alive (US Navy photo)

The aircraft is powered by two CFM56-7 turbofans, one of the most widely used jet engines in the world, with over 30,000 manufactured as of 2016. Most MPAs have four engines which provide a measure of redundancy when operating for long distances away from land. However the CFM56 is exceptionally reliable with shutdown rates around three per million flight hours. In the three years the P-8A has been in service it has yet to have an in-flight engine shutdown. Electrical power is provided by a 180KVA generator on each engine and a standard 90KVA back-up APU. With a total of 450KVA available, there is more than enough to support the mission systems with plenty of capacity for additional equipment to be fitted in future.

The P-8 has an endurance of around 10.5 hours at an economical cruising speed of around 500 knots at high altitude, with an approximate unrefuelled range of 4,500 miles. Operating at low level, the aircraft can fly in a fuel efficient regime at 180Knots, just 60m above the sea. Crews are trained to refuel their own aircraft so the P-8 can land at civilian airports and utilise standard commercial jet fuelling facilities if required. Unfortunately, when first delivered, only US tanker aircraft will be able to conduct in-flight refuelling with the UK P-8. The RAF Voyager tanker is fitted with a probe and drogue system rather than the flying boom used by the USAF. It is possible the aircraft could be modified in future to address this problem.

In US Navy service the Poseidon is operated by nine aircrew which includes the flight commander, two pilots, two tactical coordinators, two anti-submarine weapon systems operators and two electronic warfare weapon system operators. There is no dedicated flight engineer.

Although the process is far too slow, the UK has retained just enough skills and is putting the right infrastructure in place to gradually re-enter the MPA game. By selecting the P-8, the RAF will have the best platform available to conduct maritime patrol, anti-submarine warfare and search and rescue. We will consider the more complex questions about how the aircraft may be operated and weapons integration in part 2 of this article.