The U.S. Air Force was able to bomb Libya with impunity after knocking out its relic of an Integrated Air Defense System, but what if the country had actually maintained a competent IADS network?

That would pose a different challenge altogether.

Russia’s S-400 system, for instance, mixed with other overlapping missile batteries, fighter aircraft and command and control nodes, would have tested America’s ability to carry such an air raid like never before.

And that’s part of the reason why U.S. lawmakers, defense officials and the White House have been oddly unified in preventing Turkey from acquiring the S-400 alongside the F-35 joint strike fighter.

It’s not because the U.S. would attack Turkey, but because the systems its leaders are looking to acquire could be used to gather intelligence on how America’s latest generation fighter, the F-35, and possibly others, operate. That information could then end up in the hands of the Russians.

“It’s astounding to see everyone in the same direction on this,” said Rick Berger, a defense budget and military acquisition researcher at AEI and former Senate Budget Committee staffer.

The disagreement over the S-400 exacerbates the strategic and tactical concerns that exist in an already shaky alliance.

"The whole 'Should Turkey be in NATO?’ question pops up a lot, and is inevitable,” Berger said.

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The U.S. has relied heavily on Turkey’s NATO allegiance for some time, most notably by launching combat sorties against the Islamic State from Incirlik Air Base in southern Turkey. The U.S. presence at Incirlik has been seen as an important bargaining chip during ongoing tensions that stretched beyond the S-400 issue to the U.S. support for Kurdish Syrian fighters.

“We’re kind of sleep walking into this inevitability that Turkey is out of the F-35 program," Berger said. "If we don’t give them the F-35, why would they want our people there.”

The technical risks

If Turkey acquired the S-400 alongside the F-35, the technology that makes that aircraft lethal could potentially be compromised.

NATO states use a tactical data link that allows military aircraft and even ships and ground troops to share their tactical pictures in near-real time. This is called Link 16. NATO aircraft also use Identification Friend or Foe systems, known as IFF, to identify friendly aircraft in the sky.

An IFF and Link 16 interrogator would have to be integrated into the S-400 system to allow the Turkish F-35, with the transponder, to fly within lethal range of the S-400.

This opens up all Link 16 and IFF tactical data link equipment to be compromised, a former radar and weapons expert said on background.

“With the F-35 flying in close proximity to the S-400 system, over time, you could collect sensitive stealth characteristics of this F-35 and learn its detailed stealth capabilities,” the expert said.

The waveform off the Lightning II’s stealthy surfaces and its transmissions are highly classified in order to protect radar operating parameters, stealth technology and encrypted Link 16 codes.

For instance, “when you know the waveform, you can spoof them," sending a fake signal to a receiver in order to trick an operator.

Russian S-400 air defense missile systems roll at Red Square during the Victory Day military parade in Moscow on May 9, 2016. (Kirill Kudryavtsev/AFP/Getty Images)

The concern is not necessarily that the Turkish military would compromise this sensitive data, but instead that malware on the S-400 or Russian workers operating, setting up or maintaining the system would access the info.

These S-400s are highly networked, with nodes spanning hundreds of miles. There would be multiple, vulnerable nodes that could potentially broadcast sensitive data back to Russia or, perhaps, the highest bidder.

Even operating U.S. Air Force F-35s out of Incirlik Air Base could become difficult if an S-400 was nearby.

Convincing the Turkish government, particularly its authoritarian president, Recep Tayyip Erdoğan, that the move to buy the Russian system wasn’t in their best interest should have been relatively easy, Berger said.

The Turkish perspective

Pentagon officials made a last-minute extended offer to sell Patriot missiles as an alternative, but Turkish leadership was unconvinced.

“The United States failed to offer us any suitable terms," Erdoğan said Friday. "So the S-400 deal is being carried out, and we expect the systems to be supplied in July.”

Turkey has also objected to U.S. concerns by citing Greece, another NATO ally, which maintains Russia’s older S-300 missile system. But that deal was made in the 1990s, before the Kremlin reemerged as a foe to NATO. And for the time being, Greece isn’t getting F-35s.

Additionally, stealth technology is compromised by collecting lots of data over long periods of time at different orientations and at close range, the radar expert said. Tracking algorithms have dramatically improved since the S-300 was made due to increases in computational power.

S-400s outside of NATO countries would try to collect on the F-35 as well, but from “intermittent passes at long ranges, at limited aspect angles with varying clutter conditions,” which would “yield inconclusive data,” the expert said.

From the Turkish perspective, this is all political theater. But from the U.S. standpoint, this is a problem for Turkey as well, since their own F-35As could be rendered useless.

“Turkish decision-making is opaque right now because of the way Erdoğan centralized power,” Berger said.

It’s unclear, he added, whether Erdoğan and President Donald Trump are accurately conveying and understanding one another’s concerns.

But “there’s still a sense among some Turks that the U.S. is bluffing,” Berger said.

One voice

The statements so far from the Pentagon, lawmakers and the White House show that Turkey’s acquisition of the S-400 is “a step beyond the pale for a U.S. and NATO ally to take," said Andrew Philip Hunter, a senior fellow at the Center for Strategic and International Studies and a former senior executive at the Department of Defense.

“We tolerate other countries operating Russian systems in various scenarios," Hunter said. "We’ve even purchased Russian systems for the Afghans in some cases. But this is clearly marking out the S-400 as a system that’s not acceptable.”

There would still be ways to recover the U.S.-Turkey relationship and not allow it to slip too far, Hunter said.

“But if the steps toward Russia were to continue, and particularly steps toward acquiring systems that cannot be integrated into NATO systems," he added, "that would potentially widen that breach to the point where it could be a serious problem for the alliance.”

Working around Turkey to carry out missions in the Middle East isn’t impossible, just difficult. In order to continue projecting power, the U.S. may be forced to rely more on Jordan or Arab states like Qatar.

President Donald Trump talks to a pilot in the cockpit of an F-35 aircraft during a Defense Capability Tour at Luke Air Force Base, Ariz., in October. (Carolyn Kaster/AP)

Qatari officials have been eager to develop more defense ties with the U.S. and have signaled a desire to expand the American presence at Al Udeid Air Base. But even Qatar has talked with Russia about buying the S-400.

“My guess is our military folks wouldn’t be thrilled about that either," Berger said.

Not having uninhibited access to bases in Turkey would certainly have an impact on U.S. operations. But the Iraq invasion in 2003 serves as an example that the U.S. military can conduct missions in the region with or without Turkey.

“It was major impediment to U.S. plans when Turkey denied the U.S. the right to use its terrain for that operation, but we were able to work around it,” Hunter said. "There are definitely workarounds, but the fact that those workarounds exist, to me, doesn’t suggest that the alliance is any less strategic and important.”

The U.S. stance shows that a red line has been drawn on the issue, and that the Pentagon is willing to bear very substantial costs on its end.

"Not delivering the F-35s to Turkey would put huge costs on the Turks, but also on the United States,” Hunter said.

For one, the U.S. would have to find alternate suppliers for a number of parts for which Turkey is now responsible, “which they probably can do, but it’s going to impose costs,” he added.

It will also cost Turkey, though. After all, the F-35 program is good for the Turkish economy and industrial base.

“I don’t know if they understand whether they got taken by the Russians on this,” Berger said. “Yeah, the S-400 is a great system, but the price [Turkish leaders] are going to pay is massive."

The decision to buy the S-400 appears to be largely about showing that Turkey isn’t beholden to the West, Berger said. But Turkey could have made the same point by buying something else from the Russians.

“We’re not tiptoeing to ‘Do you want to be in NATO or aligned with the Russians?’ " he added. "This is basically the end of the road: the most salient military trade-off that they could make.”