The first parts of a sophisticated, Russian-supplied surface-to-air missile system, known as the S-400, arrived in Turkey on Friday.
It was a moment American officials had been anticipating for months. They had warned Turkey that purchasing the equipment would jeopardize the country’s expected receipt of American-made F-35 warplanes. And now they must decide how to react.
Here is a look at how the missile system is threatening to drive a wedge into NATO and what it means about Turkey’s relationships with Russia and the West.
What is the S-400?
The S-400 surface-to-air missile system is one of Russia’s most advanced antiaircraft weapons. It is an upgraded version of the S-300, the Soviet Union’s answer to the American Patriot missile batteries introduced during the Cold War.
The S-400, also known by NATO countries as the SA-21 Growler, has several components: a truck that carries and launches up to four missiles, and separate radars — operating on different frequencies — that network together for more accuracy.
What distinguishes the S-400 from older systems is its ability to target and attack multiple aircraft at an average range of 250 kilometers, or roughly 155 miles, and at altitudes of around 82,000 feet.
The S-400 is designed to act as the backbone of an air defense network that has several layers of defenses, such as shorter range missiles, placed around it. But not all Western defense analysts view the S-400 as a breakthrough weapon.
“It’s quite capable and at the same time it’s terribly overhyped,” said Michael Kofman, an analyst with CNA Corporation, a nonprofit research institute. Despite descriptions of the S-400 as a “magic bullet” to defend against radar-evading stealth aircraft such as the F-35, the S-400’s radars would still have difficulty tracking those types of jets to accurately target and fire at them, Mr. Kofman said.
Also unclear, Mr. Kofman added, is whether the S-400 systems that Russia exports, like the one delivered to Turkey on Friday, have reduced capabilities compared to the versions Russia uses for its own defense.
The United States is worried. Should it be?
For one thing, NATO has already tried to help Turkey with its overall air defense systems, and it’s not clear the S-400 can easily be integrated. But America’s bigger worry is the security of sensitive information about its F-35 warplanes.
Turkey has 100 or so of the advanced American jet fighters on order. It was also supposed to play a role in the manufacture and maintenance of the warplanes.
The Pentagon is concerned that Turkey will need Russian technicians to train the Turks and calibrate the S-400 system, and that in the process, Russia will learn a lot about any F-35s the Turks may have acquired — information the Americans want kept secret.
As a result, the Pentagon has threatened to cut Turkey out of its F-35 program if it proceeds with the S-400 purchase.
But Mr. Kofman, of the CNA Corporation, said American concerns were overblown. Their talking point, he said, was “not technically valid.”
The only thing the S-400 can do with its radars is track the flight profile of the F-35, something that Russia already does in the Middle East and the Baltics, as the S-400 in Syria and radar stations in Kaliningrad track American aircraft such as the F-35 and F-22 all the time, Mr. Kofman said.
Does this drive a wedge into NATO?
Beyond the Pentagon’s technical concerns, the purchase raises a number of strategic and geopolitical questions.
Analysts say it is almost unprecedented for a NATO member like Turkey to turn to Russia for such an advanced piece of military equipment.
Many NATO governments, after all, see Russia as an ever more emboldened threat to the West, and surely not a supplier worth trusting with some of a fellow member country’s most vital defensive equipment.
Turkey, too, has not seen eye to eye with Russia, most dramatically over the civil war in Syria, in which the Kremlin has backed the regime of President Bashar al-Assad, while Turkey has supported rebel factions.
So why would Turkey buy the S-400 anyway?
American interventions in Iraq and Syria have bolstered Kurdish groups seen by Turkey as terrorist separatists who threaten Turkey’s integrity and represent its most urgent security concern.
That, analysts say, is a major source of Turkey’s mistrust of the United States, and of its growing cooperation with Russia.
What’s more, Turkey for years had sought to fill a gap in its defenses by buying an American-made Patriot surface-to-air missile system, but talks with Washington failed to produce a deal. And while NATO has stationed a Patriot system on Turkish soil since the outbreak of Syria’s civil war in 2011, Ankara has insisted on buying one of its own.
With the United States retreating from the region and Russia seen as a resurgent regional power, Turkey seems to have decided to spread its bets.
Turkey and Russia have avoided clashes outside Syria, and have come to collaborate through peace talks led by Russia, Turkey and Iran.
But the S-400 purchase is a risk for President Recep Tayyip Erdogan of Turkey. Mr. Erdogan has pursued the Russian missile system despite American warnings and the damage that sanctions could do to his country’s already suffering economy, including a renewed slide in the Turkish lira.
What is President Trump’s position?
It has not aligned exactly with his defense officials’ view. The Pentagon has placed the responsibility on Turkey, warning the Turks of serious consequences over the S-400 purchase.
Mr. Trump, though, has blamed the administration of former President Barack Obama, saying the Turks felt compelled to buy the Russian system because Mr. Obama had failed to sell them American-made defense systems instead.
“It’s a mess,” Mr. Trump said at the Group of 20 meeting last month. “And honestly, it’s not really Erdogan’s fault.”