Yet defenders of the F-35 say it is a highly capable aircraft that is proving doubters wrong, with orders flooding in from Nato countries such as Germany, Canada, Finland, Switzerland, the Czech Republic and Greece in recent years.
Deployments of F-35s in Syria against Islamic State and on Eastern Europe’s frontier with Russia were particularly effective.
Retired general Jeffrey Harrigian, the former commander of the US Air Force in Europe who is now a vice-president at Lockheed Martin, said the stealth capabilities of the jets meant those deployed to the Middle East war zone could operate with impressive freedom.
“We found ourselves in very good positions relative to the Russian airplanes that were flying around, such that if something would have come up, we were fully prepared to take care of business – and the Russians knew that,” he told reporters at the Farnborough airshow on Tuesday.
In the buildup to the Ukraine war, the US and Nato allies including the UK and the Netherlands also stationed F-35s in the Baltics to deter Russian aggression.
“We knew the Russians would know where they were. And we also knew they didn’t want to have any part of dealing with F-35s,” Harrigian said.
Professor Justin Bronk, a senior research fellow for air power and technology at the Royal United Services Institute (RUSI), says the F-35 is essential to maintaining British airpower through to the 2030s, when Tempest is expected to come online.
“I think the UK should definitely proceed with the follow-on order of 27, to take the fleet to 74,” he says. “That’s more or less the functional minimum for the fleet to meet its obligations.
“Beyond that, I don’t see much fiscal room for additional orders in the foreseeable future and, in any case, if there was additional money … I would put it into weapons and maintenance and spares, to improve the combat capability and availability.”
He is sceptical about grumbling on sovereignty with the F-35, pointing out that Britain already works with international partners on the existing Eurofighter Typhoon programme and will do so for Tempest as well.
“There are certainly some trade-offs, but I think the sovereignty issue is significantly overblown,” he adds.
“The UK doesn’t have sovereign control over the Typhoon or Tempest either, because it’s beholden to the requirements and needs of the other partner [countries] – so the idea there’s some sort of mystical sovereignty involved in any of these is fairly obviously not true.”
Meanwhile, the F-35’s contribution to the British economy should not be underestimated, either.
More than 800 domestic companies work on the programme including ejector seat maker Martin Baker and Rolls-Royce, which makes the F-35B’s vertical lift system.
According to Lockheed, it has generated an estimated £45bn of exports so far for the UK and is expected to support up to 20,000 British jobs over its lifetime.
James Cartlidge, a former Conservative defence procurement minister and now shadow defence secretary, believes seeing Tempest and the F-35 as opposing choices is a false dichotomy.
He says Labour should announce a timeline for reaching 2.5pc of GDP in defence spending by 2030, as the Conservatives did during the election, and shut down doubts about funding.