By Dominic Nicholls, Defence and Security Correspondent

Telegraph Online – 1 July 2018

Britain's brand new "stealth" jets could be visible to the Russians, the US warns. Britain has taken delivery of the next-generation F-35 fighter, but officials on both sides of the Atlantic fear the secret technology could be at risk. Turkey, a member of NATO plans to buy both the F-35 fighter jet and the latest Russian Surface to Air Missile system. Experts fear operating both systems together could allow data on any vulnerabilities in the F-35 to flow back to Russia.

Britain has said it will buy 138 F-35 fighter jets and has so far committed money for 48 of the aircraft. The first four touched down in the UK in June and sea trials are due later this year from HMS Queen Elizabeth, Britain's new aircraft carrier.

A US Senator has added a provision to a Senate bill that would halt the sale of F-35 to Turkey until Mike Pompeo, the US Secretary of State, certifies the country will not also take delivery of the S-400.

"I support the transfer of F-35 advanced aircraft to Turkey, but not if they proceed with the acquisition of the Russian S-400 missile defense system,"

said US Senator Chris Van Hollen.

"This move would jeopardise the national security of the United States and our other allies. Turkey's acquisition of both systems would allow the Russians to more easily evaluate the capabilities of the F-35 and detect and exploit its vulnerabilities. That is unacceptable. This provision makes it clear that if Turkey ignores the concerns of its NATO allies and moves forward with this partnership with Putin, it will no longer receive F-35s,"

Mr Van Hollen said. Speaking to the Telegraph, Mark Francois MP, a member of the Defence Select Committee, said:

"The UK is investing a tremendous amount of money in the F-35 and part of the reason for that is the stealth technology. We wouldn't want to see anything compromise that capability and that includes the sale of the S-400 to Turkey. This will undoubtedly be causing concern in the MoD as it is fairly obvious the Russians are trying to draw them in."

Turkey has simultaneously agreed to buy 116 F-35 jets, which are 15 per cent owned by Britain, and two batteries of the S-400. The country has historically had a turbulent relationship with other Nato members, a situation made worse after Turkey's President, Recep Tayyip Erdogan, felt Mr Putin offered more resolute support than the US after the failed coup in Turkey in 2016.

Mr Erdogan sees his interests in Syria, where his forces are fighting Kurdish militia groups in the north, to be closer aligned to Russia's strategic view for the country, Confusingly, the US views the Kurdish groups as allies in the fight against both the Syrian regime and the remnants of Da'esh, also known as Islamic State. 

Speaking to the Telegraph in a personal capacity, Julian Lewis MP, Chairman of the Defence Select Committee, asked whether Turkey should be allowed to buy F-35 at all as they have

"an ambiguous record of support to our Islamist enemies and are forging an unhealthy relationship with Russia as well as emulating Putin's techniques to consolidate power."

On June 21 the roll-out ceremony for the first Turkish F-35s took place in Texas, but Assistant Secretary of State for European and Eurasian Affairs Wess Mitchell warned the program could still be halted even if Mr Van Hollen's bill fails.

"The US maintains custody of aircraft until they are transferred,"

Mr Mitchell told the Senate Foreign Relations committee on June 26.

"We can't be any clearer in saying both privately and publicly: a decision on S-400 will qualitatively change the US-Turkish relationship in a way that would be very difficult to repair."

The S-400, known in NATO terminology as the SA-21 Growler, is an anti-aircraft weapon system in service with the Russian military since 2007. It can operate with four different types of missiles with ranges from 40 km to an estimated 400 km, to create a multi-layered system. The longest-range missile has yet to enter service.

"It is typical of the Soviet-type approach,"

says Douglas Barrie, Senior Fellow for Military Aerospace at the International Institute for Strategic Studies, a think-tank.

"They want to start shooting at you as far away as they can and whittle down the number of attacking aircraft."

The long-range missiles would be able to target larger aircraft such as tankers and airborne early warning and control platforms at extended range. These aircraft have large radar cross-sections. Smaller aircraft, such as fighter jets, are harder to detect but are still not completely safe. However, any data on the latest US stealth technology would be of immense value to a potential adversary.

The Russian military would be interested in knowing in detail what a low-observable aircraft such as the F-35 looks like to the S-400 radars head-on, cross-range and moving away, Mr Barrie says. Despite any promises from Turkey, they cannot absolutely guarantee that some data might not get back to Russia.

"Any information would have considerable military utility and there is an inherent risk in those two systems being in the same military,"

he says.