Russia could destroy the F-35 from within with a missile defense sale to Turkey

• The US's NATO ally, Turkey, looks poised to destroy or deeply compromise the F-35 program from within by operating Russian missile defenses and the US-made fighter at the same time.
• Multiple generals have strongly warned against Turkey operating Russian missile defenses and the F-35, implying that Russia could learn how to detect and kill the jet through Turkey's systems.
• Turkey and the US increasingly find themselves at odds, despite being NATO allies.
• Russia hasn't built a fifth-generation fighter that can compete with the F-35, but if it perfects its surface-to-air missiles with an inside look at the stealth fighter, it may not need to.

The US's F-35 Joint Strike Fighter is the most expensive weapons system of all time and a fighter jet meant to revolutionize aerial combat, but the US's NATO ally, Turkey, looks poised to let Russia destroy the program from within.

Turkey, a partner in the F-35 program, has long sought to operate both the fighter jet and Russia's S-400 surface-to-air missile defense system at the same time.

But experts have told Business Insider that patching Russia in to NATO air defenses, and giving them a good look at the F-35, represents a gob-smacking breakdown of military security.

As such, lawmakers have tried to get the US to stop selling F-35s to Turkey, but Turkey already has two of the fighter jets, and says the S-400 is a done deal.

Generals are sounding the alarm

On Tuesday, US Army General Curtis Scaparrotti, the head of US forces in Europe, told a Senate Armed Services Committee that the idea was as bad as it sounds.

"My best military advice would be that we don't then follow through with the F-35, flying it or working with an ally that's working with Russian systems, particularly air defense systems, with what I would say is probably one of most advanced technological capabilities," Scaparrotti said.

"Anything that an S-400 can do that affords it the ability to better understand a capability like the F-35 is certainly not to the advantage of the coalition," NATO Allied Air Commander Gen. Tod Walters said in July.

Read more: Turkey says it can't accept the US's Patriot missile offer, but 2 F-35s will be delivered next month

NATO worries about "how much, for how long and how close" the F-35 would operate near the S-400s. "All those would have to be determined. We do know for right now it is a challenge," he continued.

Retired US Air Force Lt. Gen. David Deptula told Business Insider that NATO countries "don't want to be networking in Russian systems into your air defenses" as it could lead to "technology transfer and possible compromises of F-35 advantages to the S-400."

Russia wouldn't just sell Turkey the radars, batteries, and missiles and then walk away, it would actively provide them support and training. Russian eyes could then gain access to NATO's air defenses and also take a good look at the F-35.

The F-35's fate in Turkey's hands?

As NATO is an alliance formed to counter Russia, letting Russia patch in would defeat the purpose and possibly blunt the military edge of the most expensive weapons system ever built.

But the US has little choice now. Turkey has pivoted away from democracy and frequently fueded with its NATO allies since a 2016 attempted coup spurred its president, Recep Tayyip Erdogan, to consolidate power.

Read more: The US may deny Turkey F-35 sales - and now it may turn to Russia in a nightmare for NATO

Turkey holds millions of Syrian refugees and has helped stem the tide of refugees flowing into Europe. Turkey has expressed fury at the White House for years over its support of Kurds in Syria and Iraq who fought effectively against ISIS, as Turkey brands the militant Kurdish units "terrorists."

The F-35 holds advantages besides stealth, including a never-before-seen ability to network with other fighters, but the S-400 remains a leading threat to the fighters.

Russia, if it spotted an F-35 with its powerful counter-stealth radars, would still face a steep challenge in porting that data to some shooter somewhere that would track and fire on the F-35, but nobody in the US military wants to see Russia looped in to the F-35's classified tactics and specifics.

Russia has failed to field a fifth-generation fighter jet to compete with the US's F-22 and F-35 in any meaningful way, but if its missile defense systems can get an inside look at the F-35, it may not need to.