One rationale provided by the UK and Dutch governments is that suspending parts whose final destination is Israel would disrupt the global supply chain, as the parts are difficult, if not impossible, to trace.
Last year, the US Government Accountability Office (US GAO) found that over $85m worth of spare F-35 parts had been lost globally because the US government and private contractors had not determined who was responsible for tracking them.
However, arms control experts and litigants who spoke with MEE say this is clearly a case of politics, not logistics.
They can track these things within very small areas, in real time, everywhere in the world, said Martin Butcher, policy advisor on arms and conflict for Oxfam, which is involved in a legal challenge against UK arms exports to Israel being brought to the High Court.
The idea that they cant track them is absolute nonsense.
While experts say it is difficult to establish which type of aircraft Israel has used in specific attacks over the past year, it is clear that F-35s have played a key role in Israels air war on Gaza and now Lebanon.
Much of what is known comes from Israeli media reports or other public sources, including a post on Israeli Defence Minister Yoav Gallant''s X account. This post was utilised by the Danish news outlet Information and NGO Danwatch to confirm that an F-35 had been used in a designated safe zone in Gaza in July that killed at least 90 people.
However, there are other signs that the F-35 has been crucial.
Chairing a hearing before the US House Subcommittee on Tactical Air and Land Forces in December, Representative Rob Wittman said the F-35 programme had moved at a breakneck speed to deliver more spare parts to Israel.
''If you cut off the supply of spare parts, particularly on something like the F-35s, it would very quickly become unflyable''
- Josh Paul, Dawn fellow
Last year, British companies used open licences covering the F-35 programme 14 times to export items directly to Israel, nearly three times more than in each of the two previous years, according to data obtained by the UK-based Campaign Against the Arms Trade (Caat).
It is unclear when the shipments were sent in 2023, but Caat believes the jump likely indicates a heightened demand from Israel for spare parts since 7 October.
While bombs are often the focus of arms embargo campaigns, spare parts for the F-35 - and other fighter jets in Israel''s fleet - have been critical to Israel''s air war in a way that is frequently overlooked by the public, said Josh Paul, a former State Department official who resigned in protest last October.
"Modern fighter jets rely on immense amounts of continuous maintenance," said Paul, who is now a fellow at the US-based NGO Democracy for the Arab World Now (Dawn).
He estimated that for every one hour of flying, a fighter jet requires three hours of maintenance.
"If you cut off the supply of spare parts, particularly on something like the F-35s, which relies on a global just-in-time delivery chain, it would very quickly become unflyable."
Flying F-35s in seemingly unnecessary conditions over Gaza may have been useful for the Israeli Air Force to maintain fleet readiness and gain insights into the fighter jet''s capabilities in combat.
That information will also have been relayed back to the prime contractor, Lockheed Martin, the US Air Force and potentially other partner countries in the F-35 programme, several arms experts told MEE.
Lieutenant-General Michael Schmidt, who oversees the F-35 programme, said in December that Israeli F-35 users were achieving exceptional mission capability rates and the aircraft is proving resilient.
Were learning a tremendous amount and will apply lessons learnt to enhance fleet readiness across the globe, he told the House Armed Services subcommittee.
A lot of militaries are benefiting from what Israel is doing right now," said Perry of the AFSC.
"All of the air forces that have F-35s, that have ordered F-35s or that have considered ordering them, they are all benefitting from this - and, of course, Lockheed Martin itself.
The information sharing among F-35 partners is just one example of a global defence programme that operates like no other.
The consortium is managed by the Pentagons F-35 Joint Program Office (JPO) and includes seven allied countries that have contributed varying amounts to the programme''s research and development in exchange for price reductions on fighter jet purchases.
Seven other countries that are not partners in the programme have also purchased the F-35, including Israel.
Arms control experts told MEE that the F-35 is run on a just-in-time delivery system, allowing the fighter jet to send a message to alert its operators when a new part will soon be needed.
This is why many, including Butcher, are sceptical when governments say they cannot suspend F-35 components destined for Israel due to the difficulty of tracking them across a complex, multinational supply chain.
Gerard Jonkman, director of the Rights Forum, one of three Dutch NGOs challenging their government over arms exports to Israel, told MEE: Even Ikea or any company in the world knows exactly where their spare parts are coming from. So what about a plane like this?
''If your logistical system is not able to cope with international law, then you have to find a way to change your logistical system''
- Gerard Jonkman, The Rights Forum director
If one batch at a certain moment would turn out to be of bad quality, then you would need to know from where they are coming and in which planes they have been assembled.
Even if it is true that it is currently impossible to trace F-35 parts, this should be addressed, he said.
If your logistical system is not able to cope with international law, then you have to find a way to change your logistical system, Jonkman said.
When asked if components from partner countries could be tracked and traced, Lockheed Martin directed MEE to the US government.
F-35 JPO spokesperson Russell Goemaere told MEE in a statement that maintaining accountability for parts and data is "essential to ensure prudent management of F-35 financial and operational resources".
"However, most F-35 parts are part of a global spares pool procured for the benefit of all F-35 customers. Parts in this global pool are not designated for any designated end user as they are procured and are instead issued and distributed to our customers based on demand and prioritization, when needed," Goemaere said.
"While the F-35 supply chain is capable of controlling material movement based on part number/configuration, no current system, process or business rule is in place to filter out or stop the movement of specific serial numbered material to any specific country based on its country of origin."
More than just a logistical problem, those challenging governments to stop the export of F-35 parts to third countries believe their governments feel locked into the US-run programme.
The US is the government that has taken and demanded complete control over the F-35 programme, including which country can even buy it, said Frank Slijper, leader of the arms trade project at PAX, the Dutch NGO involved in the legal challenge there.
''They clearly have no interest in countries like the Netherlands or the UK messing up what is so central to American foreign policy''
- Frank Slijper, PAX project leader
They clearly have no interest in countries like the Netherlands or the UK messing up what is so central to American foreign policy.
They also believe their governments may fear that if they suspend parts, they will be seen as unreliable partners in any future defence programmes. No partner country in the F-35 programme, touted in promotional videos as diplomacy in action, is understood to have ever suspended parts.
Partner countries may also worry about the legal consequences of companies manufacturing and exporting F-35 parts if they suspend licences to third countries.
On the other hand, they point out that, unlike the United States, all the countries where litigation is currently underway are parties to the Arms Trade Treaty.
Under the treaty, arms transfers are prohibited when it is more likely than not that they will be used to commit certain human rights violations.
If they would not act on this specific case of F-35s and Israel, they lose their credibility, Slijper said.
Subcontracting companies and countries indeed have a responsibility and they cannot leave it to another state - in this case, the US - that is not part of the Arms Trade Treaty.
Jonas Devantier, the programme advisor for Oxfam Denmark, one of several NGOs challenging the Danish government, said that during their legal case, he and others learned that roughly 90 percent of the arms exports Denmark provides to Israel are through the F-35 programme.
One component made in Denmark is a pylon that releases bombs from the fighter jet. So it is very clear that it is needed for the F-35 to be used in the way that they are, Devantier said.
In March, the Danish government announced it was implementing a very restrictive approach to arms exports to Israel, which turned out to be restrictions on new export licences.
Existing licences, including those covering exports related to F-35s, remain in place.
Devantier said: "It has become more and more untenable to maintain that the F-35 fighters cannot or should not be subject to the same scrutiny as the other exports."
Hearings in most of the court cases are scheduled to be held in the coming weeks.
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