Experts warn UK faces software, dependency risks with F-35s

Britain’s reliance on the US-led F-35 fighter programme could leave it exposed to technical and strategic vulnerabilities, experts told the House of Lords International Relations and Defence Committee on 29 October.

Speaking before the House of Lords International Relations and Defence Committee on 29 October, Dr Sophy Antrobus of King’s College London said the aircraft’s structure and supply network make it impossible for any one nation to stand apart.

“If any partner nation pulls out of the system, it will not work properly,” she said. “Its interwoven nature means it is not in any nation’s interest, including the US, to limit or ring-fence parts of the programme. It works better with us all working together.”

Antrobus warned that the UK’s smaller procurement volume compared to the US could weaken its influence, noting that “the priority in Washington pushes us further down the pile” and that such imbalances could shape the country’s future access to upgrades and weapons integration.

On the issue of a possible “soft kill switch” in the F-35 software, which some analysts believe could theoretically allow the US to restrict operations remotely, Antrobus said the greater concern was the aircraft’s immense digital complexity rather than political interference. “When you buy an F-35 or anything that is that software-dependent, you are taking the risk that something can go wrong,” she said. “Worrying about it being the US Administration versus anything else is not as big a deal as some have made out.”

She cited research comparing the F-22’s roughly two million lines of code with the F-35’s nine million, noting that so many institutions contribute to its software that “it does not have to be a nefarious US Government, it could just be an incompetent individual.”

Dr Justin Bronk of the Royal United Services Institute agreed that complexity brought risk but stressed that the American testing and evaluation system is the most rigorous in the world. “Even minor faults generate extensive follow-up work because a combat aircraft has to work every time,” he said. “That’s part of why there have been delays, but it also means bugs are fixed rather than deferred.”

Addressing the idea of a software “kill switch,” Bronk said “a hard kill switch does not exist as far as I have been able to gather.” He added that any embedded control feature would be “an enormous vulnerability” for US forces if discovered. A theoretical soft restriction, such as removing access to the maintenance or software backbone, could make operations difficult over time, he said, but it would only occur in a scenario where the US had already withdrawn support across multiple areas.

“In that situation,” he explained, “they would not resupply our munitions or allow us access to their command and control systems. We are so militarily dependent on the United States that concerns about them trying to stop us fighting completely miss the point.”

Instead, Bronk urged policymakers to focus on the UK’s structural reliance on American power. “We should look at the key areas of European security where we depend not just on US support but on America doing our fighting for us,” he said. “Those gaps, such as the suppression of Russian air defences, are easier to fill than building the ability to fight while America is trying to stop us.”