Typically, a Patriot battery includes both missiles. Turkey is reported to have requested 15 batteries so as to ensure complete territorial coverage. NATO officials deemed that excessive and appear to have committed to sending up to six batteries. Germany and the Netherlands are reportedly sending two batteries each, and the United States an additional two. Each battery is likely to hold 16 interceptors. The actual battery is only manned by three people, but the support staff will likely include up to 100 soldiers per deployment.
Both types of interceptors are capable of engaging and destroying not just missiles, but also aircraft and, depending on their placement, low-flying helicopters. Patriot operators could theoretically track and destroy a large proportion of Syrian aircraft approaching parts of the border. The PAC-3, which has a forward-facing fuze and a warhead designed to intercept faster and higher-flying ballistic missiles, is sufficiently maneuverable to intercept relatively slow-flying jets. But the older, less expensive PAC-2s are better suited to an anti-aircraft role.
Both missiles provide some protection for Turkish population centers in range of Syrian missiles. Depending on where you put the radar and interceptor sites, they are also capable of protecting a zone roughly 50-100 kilometers into Syrian territory. This could bring key battlegrounds in the civil war, such as the city of Aleppo, within range.
However, there is reason to accept the NATO secretary general's pledge that "any deployment would be defensive only" and "would in no way support a no-fly zone or any offensive operation." The enforcement of a no-fly zone requires the establishment of robust and capable command-and-control arrangements and the careful deconfliction of airspace. As such, these zones have historically been handled with aircraft. The Turkish air force participated in the NATO effort in Bosnia and also hosted American aircraft that enforced the no-fly zone over Iraqi Kurdistan during the 1990s. But neither NATO nor Turkey has released any information suggesting that they are putting in place the prerequisites for an aircraft-enforced no-fly zone.
While the Patriot system can provide some anti-aircraft coverage, it would be incomplete and extremely expensive. A single PAC-3 missile costs $3-4 million. Moreover, configuring Patriots to engage lower and slower-flying targets -- like aircraft -- presents other dangers. During the 2003 Iraq War, an American Patriot battery downed a British Tornado jet, killing its crew; a U.S. Navy F/A-18 was also shot down; and a U.S. F-16 was forced to destroy a ground-based radar that had "painted" the jet.
Even against missiles, the Patriot cannot be treated as a panacea. For a start, it doesn't cover short-range rockets or artillery shells -- the only projectiles that have actually crossed the border thus far. Moreover, the system has well-documented flaws that could limit its effectiveness against a Syrian Scud attack. During the first Gulf War, the Iraqi Scuds' irregular ballistic trajectories confused the first-generation PAC-2, to the point where its hit-rate may have been startlingly low -- near zero percent, according to three independent studies.
Although low hit-rates are undesirable under ordinary circumstances, they are especially worrying in the context of WMD warheads. If the conditions are favorable, the delivery of sarin by a short-range rocket outfitted with small cluster munitions -- which the Patriot is not designed to intercept anyway -- could, according to Jonathan Tucker's War of Nerves, "generate a lethal concentration of the nerve agent over a 500 meter area, not including downwind spread." However, the actual number of casualties would depend on other environmental factors and Turkish preparedness, thus it would be very difficult to assess with any accuracy. Nevertheless, a very small number of successful strikes could have a disproportionate strategic effect.
While improvements have been made since, the PAC-3 has yet to be tested against Scuds in battlefield conditions. Critically, if Syrian Scuds break up while in flight -- a common occurrence when Iraq used similar missiles during the first Gulf War -- the interceptor could be confused and miss its target.
The upshot of all this is that the Patriot deployment serves two purposes. First, it serves as a defensive move, aimed at protecting Turkish territory against a narrow range of threats. Second, it acts as a tangible political signal, with NATO personnel operating in Turkey. Not quite a trip wire, but better than reassuring words. In short, both Turkey and NATO are eager to maintain flexibility. Turkey has been unwilling to make the political decision to engage Syrian targets on Syrian territory other than in sporadic time- and space-limited retaliatory salvos. The deployment of Patriot missiles is not a step to intervention, but a compromise that keeps NATO at arms-length.