MOSCOW — In confirming the deployment of its S-300 and state-of-the art S-400 missile-defense systems in Syria, the Kremlin boasted six months ago that it had secured the country’s air bases from American cruise missiles.

But after a barrage of U.S. Tomahawk cruise missiles hit the Syrian government air base at Shayrat on April 7, where some Russian military personnel were stationed, consternated Russians took to social networks asking: “Where the hell were the vaunted S-400s?”

“Am I the only one who doesn’t understand why our S-400s…. didn’t shoot down the American rockets?” asked one Twitter user.

Я одна не понимаю, почему наши C400, находящиеся неподалёку, или сирийские С300 не сбили американские ракеты???

— Leyla (@agentleyla) April 7, 2017

The Kremlin first deployed the “Triumph” S-400 system in Syria in 2015 after Turkey in November that year shot down a Russian warplane Ankara said had strayed into Turkish airspace. The system uses a package of four different types of missiles to account for various incoming weapons and aircraft: one has a long range of 400 kilometers, and another a range of only 40 kilometers, providing overlapping blanket coverage. The system is capable of downing aircraft, drones, and cruise missiles including Tomahawks, the RIA state news agency reported at the time.

Russian and Western military analysts, however, say that the system was positioned too far away from the Shayrat air base to be effective against the April 7 strike, which used cruise missiles that skim the earth at about five meters off the ground, fly at subsonic speed, and follow their own flight paths.

“All this talk that we have secured the whole of Syrian airspace is artistic whistling,” said Pavel Felgengauer, a Moscow-based military analyst, and suggested this boasting was intended to boost the sale of arms showcased in Syria.

“They certainly can’t [intercept cruise missiles] at that distance from their location. At the very most, they can defend the nearest approach of the base where they are located,” he said.

The S-400 air-defense systems are located at Russia’s air base at Latakia and its naval base at Tartus. The strike, which hit the Shayrat air base near Homs more than 75 kilometers away from the city of Tartus and more than 120 kilometers from Latakia, meant the American cruise missiles were safely out of the Russian air-defense system’s effective range for cruise missiles, he said. “You can more or less defend a perimeter of about 40 kilometers.”

Justin Bronk, a defense analyst at the London-based think tank Royal United Services Institute, agreed, saying that despite the sophistication of the S-400’s radar — which covers up to 400 kilometers at higher altitudes — the system would encounter problemswith targets at low altitudes farther away. “Any rough terrain between the radar and the flight path of the cruise missiles will prevent that system, in this case at Latakia and Tartus, engaging,” said Bronk.

“Also, while the S-400 is advertised as having an anti-cruise missile capability, it is more geared toward ballistic missiles coming in from very high angles, very quickly, and other tactical aircraft,” he said. “It’s more geared toward those kinds of targets than subsonic, land-skimming missiles.”