The S-300s need to be kept in perspective. With their considerable range, they cover the full spectrum of aerial threats. They can target strategic enabler aircraft, such as aerial refueling tankers and early warning aircraft, and defend against low-flying cruise missiles. But these missiles — indeed, any surface-to-air missile — are completely useless against the Syrian rebels, who have neither an air force nor the munitions the S-300s are designed to combat.

When integrated in an overlapping and mutually supporting integrated air defense system — as it would be in Syria — the S-300 is a sophisticated weapon. Typically it operates in concert with several other surface-to-air missiles. Short-ranged but versatile point-defense systems — such as the Pantsir-S1, which Syria operates, and the Tor missile system — work to shield the S-300 from enemy anti-radiation missiles and other threats.

However, the S-300s are vulnerable to attack when they are deployed outside larger missile defense networks. For this reason, the batteries will be of little use to non-state actors such as Hezbollah and jihadists. Technically the missiles are mobile, but in reality the batteries are not very maneuverable and are highly conspicuous. Moreover, their radar emissions make them easy to detect. Non-state actors would be better served using other, lower-tech surface-to-air missiles, such as the 9K33 Osa and the 9K35 Strela-10.

In addition, S-300s are complex weapons that require significant expertise to operate, and it is unclear whether the Syrian military has received the requisite training. Given their sophistication, S-300s would necessitate several months of training to acquire basic competency. If Syrian crews have not already trained in Russia, then Russian personnel would have to at least partly operate the missile systems.

A Tool for Deterrence?

While the S-300s are worthless in the fight against Syrian rebels, they are nonetheless useful for other reasons — namely, discouraging any military intervention. Once fully integrated into the Syrian air defense network, the S-300s will help deter foreign airstrikes. Certainly the batteries alone will not be able to repel a NATO or Israeli air campaign, but they will raise the risk of damage and casualties involved in an intervention. (Moreover, if Russian personnel are needed to operate the systems, their presence would also deter military intervention.)

In addition, the S-300 would enable Syria to strike deep into Israeli and Lebanese airspace. This would threaten a key aspect of Israel's military dominance of Syria. Israel has long been concerned with the presence of S-300s in the region, so it comes as no surprise that Israeli Defense Minister Moshe Yaalon warned of an Israeli response in the event Syria acquired the missiles. (Yaalon also said the delivery had not yet been made.)

Diplomatic efforts are expected to continue in hopes of convincing Russia to halt delivery. If these efforts fail, Israel has several options to disable the systems, including stand-off cruise missile strikes and AGM-78 (or, possibly in the future, AGM-88) anti-radiation missiles.

If confirmed, the delivery of S-300s will damage Israeli-Russian relations. Russia argued that if it did provide Syria with the missiles, it did so only out of contractual obligation, which predates the civil war. However, the timing of the alleged delivery sends a political message. Russia is unhappy with the European Union for lifting its weapons embargo to Syria, and it is unhappy with the United States for refusing to strike a larger bargain to work with Russia on the Syrian issue. The delivery could be a message to the West that Moscow still has leverage.

Beyond the alleged delivery of the S-300 system, it is important to highlight the sheer scope of Russian support for al Assad. This support includes economic and financial aid, the delivery of spare parts for military equipment and, according to a document published May 30 in The Washington Post, other weapons and ammunition germane to the ongoing conflict. At the same time, Russia is organizing another peace conference with the United States to show that it can play a role other than al Assad's primary weapons supplier.

Absent a fundamental understanding with the United States on more strategic issues, Russia's core interest is to sustain al Assad and prolong the conflict. For now, it is abundantly clear that Moscow is not ready to sacrifice its influence in Damascus.