The UK’s multi-billion-pound fleet of F-35 fast jets can only perform all its required missions one third of the time because of a lack of engineers, spare parts and unexpectedly high corrosion at sea, an official report has revealed.
The poor performance rate is despite Britain’s expectations from its 37 stealth aircraft being “significantly” lower than a global target for all F-35B planes, which are also operated by the US Marine Corps, according to the National Audit Office (NAO), the spending watchdog.
The Ministry of Defence (MoD) is already spending £11bn at a minimum on the programme – led by the US defence giant Lockheed Martin – since its inception in the 1990s in partnership with the US and a number of other nations. The US is the lead recipient of the aircraft and has the main control over the project.
In a critical report, the NAO predicted the whole-life cost of the F-35 capability to the UK – if the government purchases the full stated aim of 138 of the aircraft that are kept in service until 2069 – would come to £71bn, including personnel and support costs.
It said an estimate forced out of the MoD was slightly less, at £57bn, but this did not include support costs such as money spent on fuel and infrastructure.
Neither estimate included the costs of weapons.
Gareth Davies, head of the NAO, said: “The F-35 programme offers significantly improved capability and considerable economic benefits to the UK. But the capability benefits are not being fully realised due to delays, infrastructure gaps and personnel shortages.
“The MoD now needs to decide where to prioritise its resources to improve capability in a way that maximises the full benefits of the F-35 programme to the UK.”
Between October 2024 and January 2025, no aircraft were available “to perform any mission” because they were undergoing maintenance, the report said.
The rates have since improved temporarily as many of the jets joined HMS Prince of Wales, the Royal Navy’s aircraft carrier, on a deployment to Asia.
But it is not thought this improved performance will be sustained.
“The UK’s availability problems are largely driven by slow maintenance activity and a lack of spare parts, as well as an emerging issue with higher corrosion than expected in maritime environments,” the report said.
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The National Audit Office flagged another issue, making the UK’s F-35 less formidable fighting machines.
It said there has been a delay in integrating missiles on to the jet that will enable it to hit targets from a safe distance.
At present, the British F-35s are only armed with bombs, which means they must fly over a target to hit it, raising the risk of the aircraft being spotted by enemy air defences and shot down despite its stealth profile.
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There is a plan to integrate so-called stand-off weapons on to the jets, but not until the 2030s, the NAO said.
The UK has said it will buy a total of 138 F-35 jets but has so far only committed to 48 of the B-variant, which operates from aircraft carriers but has a shorter range than the land-based A-model.
Of them, 38 have been delivered, with another 10 on order, but one was lost in an accident, meaning the size of the current fleet is 37.
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The delivery rate is behind schedule largely because of decisions by the UK to slow the procurement over the past 15 years to save money.
This is a false economy though, as it pushes up the overall cost and slows the delivery of what is a vital capability.
The government said last month it plans to include at least 12 F-35As in its next purchase. These aircraft also have the capability to carry nuclear bombs as part of a NATO mission.
