A longtime US ally has kept a deadly insurgency at bay, helped by squadrons of American-supplied military aircraft.
When US foreign policy abruptly changes, the aircraft remain — but contractors, spare parts and badly needed software updates suddenly disappear. Within weeks, more than half the aircraft are grounded. Four months later, the capital falls to the rebels.
This was the reality for Afghanistan in 2021. After a US withdrawal disabled most of Kabul’s Black Hawk helicopters, the cascade effect was swift. “When the contractors pulled out, it was like we pulled all the sticks out of the Jenga pile and expected it to stay up,” one US commander told US government researchers that year.
Today, a similar spectre haunts US allies in Europe. With the US cutting off military support to Ukraine in an abrupt pivot towards Russia, many European governments are feeling buyers’ remorse for decades of US arms purchases that have left them dependent on Washington for the continued functioning of their weaponry.
“If they see how Trump is dealing with [Ukrainian President Volodymyr] Zelenskyy, they should be worried. He is throwing him under the bus,” said Mikael Grev, a former Gripen fighter pilot and now chief executive of Avioniq, a Swedish defence AI company. “The Nordic and Baltic states need to think: will he do the same to us?”
Such is the concern that debate has turned to whether the US maintains secret so-called kill switches that would immobilise aircraft and weapons systems. While never proven, Richard Aboulafia, managing director at consultancy AeroDynamic Advisory, said: “If you postulate the existence of something that can be done with a little bit of software code, it exists.”
In practice, it may not even matter because of how already reliant advanced combat aircraft and other sophisticated weapons — such as anti-missile systems, advanced drones and early warning aircraft — are on US spare parts and software updates.
“It is not as simple as a kill switch,” said Justin Bronk, senior research fellow at the Royal United Services Institute (Rusi). “Most European militaries depend heavily on the US for communications support, for electronic warfare support, and for ammunition resupply in any serious conflict.”
Europe’s reliance on the US, meanwhile, has been rising, with America accounting for 55 per cent of Europe’s defence equipment imports between 2019 and 2023 — up from 35 per cent in the previous five years, according to the Stockholm International Peace Research Institute.
Sir Ben Wallace, former UK defence secretary, said that, if he were still in post, his first response would have been to commission “an appraisal of our dependencies and vulnerabilities across international partners — including the US”. This would allow reflection “on whether there needs to be any strategic changes”.
Combat aircraft
Trump has repeatedly stated his intent to buy — or take over — Greenland, an autonomous territory within the kingdom of Denmark. Citing the Arctic’s strategic importance, Danish ministers have signalled they will try to reinforce the island — potentially by expanding an airport runway to accommodate US-bought F-35 fighters.
But, for this one particular mission, those jets may well be next to useless. “What’s the point of Denmark sending F-35s to protect Greenland?” asked Sash Tusa, an aerospace and defence analyst, pointing to the uncertainty of whether the F-35s would fly — if the US did not want them to.
The plane relies on continuous updates and maintenance support from the US through its Autonomic Logistics Information System — which is to be replaced by a successor programme known as Odin, the Operational Data Integrated Network. The systems manage everything from mission planning and threat databases to maintenance diagnostics.
“The problem with really sophisticated defence equipment is that [it needs] so much support from the vendor, that if the vendor decides to stop supporting [it], the equipment stops working, if not instantaneously then very, very quickly,” said Tusa.
“The question they will be thinking is ‘how do you add US-proofing into your defence structure?’” More than half of Europe’s advanced combat aircraft — mainly the F-35 and the F-16 — are bought from the US.
Even before the Trump era, in the early stages of the F-35 programme, the UK — a top buyer that makes many parts for the plane — asked for guarantees of “operational sovereignty”. Some assurances were given in 2006, but no US ally has Washington’s level of access to the source code for the system.
Lockheed Martin said that, as part of its government contracts, the company delivers “all system infrastructure and data required for all F-35 customers to sustain the aircraft”. Foreign military sales are “government-to-government transactions, so anything further is best addressed by the US or respective customer governments,” Lockheed added.
Switzerland’s defence department recently stressed its F-35 could be used “autonomously” after facing questions about US influence over the aircraft. But it added that no advanced western fighter jet was fully independent from US secure data communication systems and GPS satellite navigation — even those made by European manufacturers.
The UK’s nuclear deterrent
Britain’s deterrent has come under particular scrutiny because it relies on submarines armed with Trident ballistic missiles. These missiles are leased from the US and regularly return to the US base in King’s Bay, Georgia for maintenance. Missile testing is also carried out under US supervision at Cape Canaveral in Florida.
This reliance is a constraint on the independence of the system, but it is unclear whether it would affect UK operations after a matter of months or years, according to analysts.
Malcolm Chalmers, Rusi deputy director-general, said the prospect of the US deciding to stop servicing Britain’s Trident missiles would be “very unlikely”.
“It would be the end of the special relationship between the UK and the US to have a sustained cut-off of that sort,” said Chalmers. Trident is also part of the Mutual Defence Agreement between the US and UK that was prolonged indefinitely when it was re-ratified last November.
However, Nick Cunningham, analyst at Agency Partners, said the Trident missiles remain a “critical point of vulnerability for the UK”. Given the role the US plays in maintenance, he argued Britain should at least investigate the possibility of using France’s M51 submarine-launched ballistic missiles. France and Britain are the only nuclear powers in Europe.
Data and intelligence
One defence industry source argued that important parts of the intelligence, surveillance and reconnaissance airborne fleet in Europe was “effectively mortgaged to the US and predicated on their collaboration”.
Specific examples include the UK’s Rivet Joint spy planes, P8 Poseidon submarine hunters (used by Norway and ordered by Germany), Wedgetail early warning aircraft, and Protector drones.
Many European nations use the US Reaper drone, made by General Atomics, which relies on US-provided satellite communication links and software support. Italy and France needed a lengthy US permission process to equip the drones with missiles.
The concern in European capitals is not so much about specific weapon systems but the potential for the US to withdraw communications support and information sharing across any platform, from fighter jets to Chinook and Apache helicopters as well as air-defence systems such as the Patriot.
“There is an obvious concern over the reliability of the US as your key defence partner,” said Douglas Barrie, senior fellow for military aerospace at the International Institute for Strategic Studies. The recent abrupt turn in US foreign policy “calls into question a whole range of things the world has taken absolutely for granted”.
A lasting defence partnership?
While Donald Trump may have rattled the transatlantic alliance, Joachim Finkielman, director of DI Danish Defence and Security Industries, said day-to-day contacts on the industry side continued as normal. “There is a lot of uneasiness about what’s going to happen, but up until now we haven’t felt any changes in the relationship with the US.”
Finkielman noted that Denmark made more than 100 parts for F-35 aircraft itself, and was one of many national suppliers. “I don’t know what capability the US has to produce them if they don’t get the Danish elements,” he said.
The chief victim of the uncertainty, meanwhile, is just as likely to be the US arms industry, rather than its European customers.
US defence companies have long used the implicit security guarantee of Washington’s favour as a marketing tool for their bigger-ticket items such as fighter planes. But Tusa said the US showing its willingness to cut off support was “utterly fatal” for the sales pitch.
“Trust is something you can only break once,” he said.
Shares in America’s leading defence groups have significantly lagged those of their European rivals, which have boomed since Trump’s return to the White House. Though no US orders have been cancelled, few doubt that Europe will begin taking a more independent approach.
“It basically signals the start of the end of the western alliance, or at least the part of it involving the US,” said Aboulafia. “Heaven help the US arms industry. This is catastrophic from an export standpoint.”
