As the Trump administration weighs options for responding to a Syrian chemical attack that reportedly killed scores of civilians, Russia has threatened to shoot down any rockets the United State flames at the Syrian regime.

That threat is a bluff: Russia's air-defense systems in Syria possess only a limited ability to reached cruise missiles, the Pentagon &# x27; s favor munitions for precision attacks on high-profile targets.

But it &# x27; s a bluff the White House should take seriously. Russia might not be able to shoot down American weapons, but it can retaliate in other ways if the U.S. strikes Bashar al-Assad's government.

The back-and-forth threats between Washington and Moscow began after as many as 40 people died in an alleged chemical attack on Douma, a rebel-held town in the Eastern Ghouta region north of Damascus. In April 2017 in response to an apparent regime gas assault the same month, U.S. forces lobbed 59 Tomahawk cruise missiles at Shayrat air base in western Syria, destroying some warplanes there.

Apparently fearing a similar attack this month, Alexander Zasypkin, Russia &# x27; s ambassador to Lebanon, told a Hezbollah-run T.V. station that Russia would fight back this time. “If there is a strike by the Americans, then … the missiles will be downed and even the sources from which the missiles were fired, ” Zasypkin said in Arabic, according to The New York Times .

President Donald Trump shot back on Twitter: “Russia vows to shoot down any and all missiles fired at Syria. Get ready Russia, because they will be coming, nice and new and &# x27; smart-alecky !&# x27; You shouldn't be partners with a Gas Killing Animal[ sic] who kills his people and enjoys it! “

Trump is right in implying that Russia &# x27; s S-4 00 air-defense systems probably can &# x27; t stop U.S. missiles. Moscow deployed two S-4 00 batteries: one at Hmemmem air base where Russian warplanes are stationed and the other near the port city of Lattakia, where Russian ships often visit.

” Cruise missiles can' hide' in the ground clutter that affects radars when they try to see very low .”
— Philip Coyle, former Pentagon official

The S-4 00 is roughly equivalent to the U.S. military &# x27; s own Patriot air-defense system and, in theory, can target aircraft and weapons as far as 250 miles away. In practice, the S-4 00 “will have significant engagement-range restrictions in real combat conditions, ” Ted Postol, a missile expert at the Massachusetts Institute of Technology, told The Daily Beast.

Overall, air defenses are merely 30 -percent effective, Philip Coyle, formerly the Pentagon &# x27; s top weapons-tester, told The Daily Beast. Five out of seven American-made Patriot rockets apparently missed or malfunctioned when Saudi forces tried to intercept a bombardment of high-flying ballistic missiles that Yemeni rebels fired at Riyadh in late March.

Air defenses are even less effective against cruise missile, which typically fly at treetop level.

“Cruise weapons can &# x27; hide &# x27; in the ground jumble that affects radars when they try to see very low, ” Coyle explained.

And the rough terrain of western Syria offers cruise missiles plenty of hiding places. For that reason Russia clearly has struggled to build an effective air-defense network in the region. In addition to the S-4 00 s, the Kremlin has sent to Syria several short-range surface-to-air missile launchers and even air-defense-optimized warships, hoping to plug various gaps in the S-4 00′ s coverage.

But there are more mounds in the region than Russia has missile launchers, ships, and radars. It &# x27; s worth recalling that Russian defenses apparently didn &# x27; t fire on any of the 59 Tomahawks that U.S. warships launched in 2017, even as some of the missiles reportedly flew within 30 miles of the S-4 00 launcher at Hmemmem.

“The Russian radars totally failed to detect them, ” wrote Tom Cooper, an aviation expert and author.

Russia probably can &# x27; t stop the U.S. from striking the Syrian regime with a onslaught of low-flying rockets, but that doesn &# x27; t mean the Kremlin &# x27; s reprisal threat isn &# x27; t a serious one.

“The Russian statement … should be taken very seriously as it is basically a warning that Russia will not stand by idly, ” Postol said. “It is in effect a political statement that indicates the Russians will try to find some style to respond to an American attack on Syrian forces.”

Zasypkin, the Russian ambassador, specifically mentioned launch “sources” as possible targets of Russian retaliation. The U.S. tends to launch Tomahawks from submarines and warships, although there are air-launched models, as well. It &# x27; s worth noting that Russian forces-out have a habit of staging mock assaults on American naval boats and flying dangerously close to U.S. warplanes.

In April 2016, Russian Su-2 4 assault airliners repeatedly buzzed the destroyer USS Donald Cook while the vessel sailed in international waters in the Black Sea. A Pentagon spokesman called the Russians' actions” provocative and unprofessional .” The American rebuke didn't stop Russian planes from tailing U.S. bombers at least twice in 2017.

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The Kremlin might not be able to reliably shoot down cruise missiles, but it is perfectly capable of menacing the ships and planes that launch those missiles.

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