The United States and its allies have a few options if they proceed with an intervention in Syria, a prospect that seems increasingly likely. A limited punitive strike on critical targets meant to discourage future use of chemical weapons would be the simplest operation. Another option would be to target the Syrian regime's chemical weapons delivery systems and storage facilities, but this option would require significantly more resources than the limited strike, and the risk of mission creep would be high.

Another problem with targeting the regime's chemical weapons is that such weapons are notoriously difficult to destroy. Therefore, the West could elect to deploy ground forces to secure the chemical weapons and ensure their destruction. Such a mission would be tantamount to a full-scale invasion, and thus we believe it is very unlikely.

In general, the larger and more complex the operation, the more time it will take, the more of a leading role the United States will have to assume and the more obvious the force buildup will be.

Limited Punitive Strike

A limited punitive strike on regime targets is the least risky option and requires the fewest resources. This option would seek to demonstrate American and allied credibility by striking regime targets, including command and control facilities and other high-value and symbolic targets. The purpose of a punitive strike would be to dissuade the al Assad regime from the further use of chemical weapons in the civil war without crippling the Syrian regime itself.

Target Set

In this scenario there are more possible targets than the West is interested in attacking. Command and control facilities will likely be prioritized, driving home the message that the regime leadership, particularly the military leadership, would pay for the decision to use chemical weapons. However, Bashar al Assad himself would probably not be targeted because his death would tie the coalition deeper into the conflict than it wants to be.

Specific facilities that may be targeted are the Defense Ministry, the Air Force Intelligence Directorate, the Political Security Directorate, the Interior Ministry, the 4th Armored Division and Republican Guard headquarters in Damascus, the headquarters of the three Syrian army corps and various key communication and command and control facilities across the country. The specific artillery units that are believed to have participated in the chemical weapons attack could also be on the list.

Assets Required

In total, the United States and its allies would need to strike fewer than a hundred targets in such a mission, although some targets would require multiple munitions and repeated strikes. The majority of these targets could be engaged with non-penetrating cruise missiles, but those with hardened defenses or those that are buried underground would require bunker-busting munitions.

Given U.S. resources and their current deployment, Washington is already in a position to commence a limited punitive strike. A crucial advantage is that the United States would not need to deploy tactical aviation in this strike and would not need to penetrate the Syrian air defense network with non-stealth warplanes. The United States already has four Arleigh Burke-class destroyers in the Eastern Mediterranean. Two of the destroyers can carry up to 96 Tomahawk cruise missiles, and the other two can carry as many as 90 Tomahawk missiles. In reality, the vessels carry other missiles, such as air defense missiles, so the Tomahawk payload is usually much less -- about half would be a good estimate. Therefore, it can be assumed that the four destroyers can deploy around 180 Tomahawk missiles.

If the payload of the nuclear-powered cruise missile submarine that is likely nearby is added, then the number of Tomahawk missiles on U.S. naval vessels already in theater is at least 334 -- and likely more because other nuclear attack submarines are almost certainly in the region. If needed, strategic bombers and even tactical fighters can deploy air-launched cruise missiles such as the JASSM (Joint Air-to-Surface Standoff Missile) from beyond the range of Syrian air defenses. These aircraft can stage out of Europe and the Middle East or, in the case of the bombers, can even come from the continental United States.

For hardened targets, the United States can rely on B-2 bombers flying missions from the continental United States. Each B-2 can carry 16 2,000-pound (about 900 kilograms) penetrating bombs or 8 5,000-pound bombs, enabling it to strike multiple targets in one mission.

Cripple the Regime's Chemical Weapons Delivery Capability

Should the United States and its allies decide to take the mission a step further, they could attempt not only to discourage the further use of chemical weapons but also to remove the regime's ability to use the weapons. The command, control and communication facilities would still be targeted, but the operation would also need to strike at a much wider network of targets and their associated defenses.

Target Set

The mission would focus on the three main ways the regime can deliver its chemical weapons: the air force, the ballistic missile force and the artillery force.

Although several regime airfields have been neutralized or captured by the rebels, several others are still operable. In theory, aircraft from at least 13 airfields can participate in a chemical weapons attack. To neutralize an airfield, the United States can crater the airfield, strike parked aircraft, destroy fuel and ammunition stores and disable ground control, radar and maintenance facilities. Some of the airfields contain a considerable number of aircraft hangars and bunkers. For example, the Tiyas air base has some 30 aircraft shelters, not all of which can survive a Tomahawk strike.

Battlefield use during the conflict has significantly diminished the Syrian ballistic missile force. At least half of the regime's ballistic missile inventory has been expended in strikes against rebel-held territory, leaving approximately a couple of hundred missiles at most. Syrian ballistic missiles, especially the larger ones, are mostly concentrated in a few bases around the country, of which the 155th and 156th brigades based in al-Qutayfah appear to be particularly prominent. At these bases the Syrians have constructed several underground drive-in vehicle storage bunkers to protect their transporter erector launchers as well as other underground bunkers for missile storage. Other notable bases that house ballistic missiles include the Hirjillah army barracks and the Mezze and Dumayr tactical surface-to-surface missile storage facilities. Roughly one-third to one-half of the chemical weapons inventory is believed to have been assigned for ballistic missile delivery prior to the Syrian civil war.

The best estimates for the Syrian army's remaining artillery inventory ranges from 1,000 to 2,000 pieces, including towed, self-propelled and multiple-rocket artillery. As the conflict has progressed, the Syrian army has dispersed its artillery holdings in support of its widespread operations. While the artillery pieces are not located in hardened positions, their dispersal complicates their targeting.

Assets Required

Adequately neutralizing all three forces, and thus crippling the regime's ability to carry out chemical weapons attacks, would require a significant contribution of resources by the United States and its allies. The risk of mission creep is high, and the campaign would tie the United States deeply into the Syrian conflict. Simply eliminating the bulk of the regime's artillery and air force would instantly tilt the balance of power toward the rebels, implicating the United States in the responsibility of post-al Assad Syria. The psychological impact of such a campaign should also not be underestimated; loyalist forces under incessant air attack while fighting on the front lines against the rebels would be under considerable stress.

Significant post-strike analysis would be necessary in such an expansive campaign, and the effort to neutralize the regime's artillery assets in particular would require extensive tactical and intelligence, surveillance and reconnaissance assets. Given the need to operate within the range of Syrian air defenses with non-stealth aircraft, a comprehensive suppression of enemy air defenses campaign would also be necessary. The Syrian air defense network has suffered several blows during the civil war but remains dense and dangerous.

Many more Tomahawk-equipped vessels would be required for the initial campaign to take out air defenses as well as the follow-on strikes, and U.S. Navy carriers with tactical aviation assets, especially electronic warfare aircraft such as the EA-18G Growler, would need to be deployed. Indeed, electronic warfare would figure prominently in such a campaign, from jamming to cyber attacks. At least one super carrier would be needed, but more could be deployed depending on the number of tactical aviation squadrons sent by the U.S. Air Force and allied countries.

Without short-range basing from countries such as Cyprus, Turkey, Jordan or Greece, operations by tactical fixed-wing aircraft would be greatly complicated because of the limited combat radius of those aircraft. The deployment of combat search and rescue elements would also necessitate forward bases (or aircraft carriers) close to Syria. In total, at least 400 Tomahawk missiles would likely be needed for the operation before a comprehensive fixed-wing campaign could commence -- more than twice the number fired during the intervention in Libya. Such a campaign would require a variety of munitions, including anti-radiation missiles, cruise missiles, penetrating bombs, air-to-air missiles, gravity bombs and air-to-ground tactical missiles.

Notably, several variables can shape the nature of the conflict. There are hundreds if not thousands of different orders of battle that can be deployed based on wide-ranging factors, such as the allies' commitments, available basing, cost, commanders' preferences and enemy resilience. For example, something as simple as whether Turkey joins the mission dramatically alters the scenario, immediately bringing 200 or more tactical fighters to the operation (by the simple fact of their being within range and Turkey being vulnerable to retaliation and operating accordingly).

Secure the Chemical Weapons in Syria

The most ambitious and risky operation would be to attempt to secure the regime's chemical weapons to definitively prevent their further use. This operation would probably also signal the demise of the al Assad regime. In many ways, this option would be synonymous with an invasion of Syria, since any attempt to secure the Syrian chemical weapons arsenal would necessitate significant ground forces. It is for this reason that we believe the likelihood of this option to be very remote.

Target Set

Scant information is publicly available on Syria's chemical weapons program. However, Syria is not a signatory to the Chemical Weapons Convention, which outlaws the production, stockpiling and use of chemical weapons, and until July 23 the regime had not publicly admitted to possessing the weapons. The al Assad regime is suspected of having VX, sarin, tabun and mustard gas, and it purportedly can produce a few hundred tons of chemical agents per year.

Several major storage and production sites are believed to be located near Homs, Hama, Eastern Damascus, Aleppo, Latakia and Palmyra. An additional 45-50 smaller facilities are believed to be spread across the country. While the United States and other Western allies have proved that they have active intelligence and surveillance of numerous sites, it would be nearly impossible for the entire stockpile to be accounted for at any one time, and it can assumed that all locations are not known.

Chemical weapons are difficult to destroy completely. The most common method is incineration at very high temperatures over a sustained period of time in a contained system. Munitions used by the military almost never reproduce these effects, especially the ones designed to penetrate a hardened structure. Another problem is the sheer volume of material. Estimates put Syrian stockpiles in the hundreds of tons of various types.

The most likely result of strikes on hardened facilities holding chemical weapons is the destruction of some of the material and the release of some into the atmosphere while the rest remains protect by the collapsed structure in rubble. In other words, a strike would succeed in destroying the material only partially while potentially causing collateral damage (many of the facilities are near populated areas) and only temporarily denying the regime the use of any remaining stockpiles.

Assets Required

Securing all of Syria's chemical weapons would necessitate a comprehensive suppression of enemy air defenses campaign. This first step would require strategic and tactical air assets combined with naval platforms, similar to the steps taken to eliminate the chemical weapons delivery capability. However, the difference is that securing the weapons would also require ground forces to be deployed in the country.

Securing even a few chemical weapons manufacturing or storage facilities would require the deployment of numerous detachments of special operations forces. Such a deployment would likely be preceded by the seizure of a Syrian airfield, which would serve as a temporary base for the operations. After the initial campaign to suppress the regime's air defenses, all threats within the vicinity of the airfield would be targeted and special operations forces would be flown in for either a combat drop or air landing. From there, the airfield would be used as a temporary bridgehead to launch several smaller operations aimed at grabbing specific sites.

The benefit of such an operation is that it would quickly put highly trained assets on the ground in moderate numbers with no buildup necessary in neighboring countries, meaning that tactical surprise could be achieved. Once the bridgehead is established, it would then be used as an air bridge to bring in reinforcements such as the 82nd Airborne Division. Absolute dominance of the airspace would have to be maintained during such an operation.

Chemical weapons are difficult to comprehensively eradicate; in about four decades the United States has destroyed only about half of its stockpiles. Units seizing chemical weapons sites could not simply strap C4 explosive blocks to them for the same reason that cruise missile strikes would not work: little is destroyed and much of it would just be flung around, risking unintended contamination and only temporarily denying the material to the enemy.

A comprehensive scenario that entails the seizure of all known stockpiles and roots out any missed supplies would essentially entail a full-scale invasion of Syria. The U.S. military reportedly estimates that it would need 75,000 troops to secure the entire network of Syrian chemical weapons. This is probably a low estimate. This option would be very complex and multifaceted. Again, a requisite suppression of enemy air defenses campaign would have to take place so the United States could dominate the airspace. Ground forces would have to be bought into theater in numbers, primarily in Jordan or Turkey. An amphibious component involving U.S. Marines could be utilized to establish beachheads on the Syrian coast. Special operations forces could also be tapped in conjunction with the 82nd Airborne Division to seize critical airfields to open up further fronts or capture time-sensitive targets deep in the Syrian core.

This would take a lot of time. Similar buildups for Desert Storm and Iraqi Freedom took months. There would be little to no strategic or tactical surprise, and the United States and its allies would rely on raw firepower and rapid movement. This would be a full combined arms operation, where air and naval assets would facilitate the movement of ground forces.

This is the option with the greatest potential for bogging down forces in an occupation. Chemical weapons are hard to deal with and require time to destroy and longer still to move elsewhere and destroy. Either way, a standing army will find itself in Syria for at least a few months. Any form of mission creep into nation re-stabilization or building extends the timeline indefinitely. Even if the invasion went well, as it did in Iraq, the occupation period creates an opening for guerrilla or insurgent warfare waged by the fallen regime, Islamist extremists, disenfranchised rebels or all of the above.