It is important to fully understand the limits and capabilities of the Syrian chemical arsenal. It is vast and its delivery means are numerous, but there are many variables that severely constrain the employment of these weapons against the advancing rebels. Despite the rebels' lack of nuclear, biological and chemical protective equipment, a serious effort by the regime to change the tide of battle through chemical warfare would not be effective enough to cripple the rebel forces and would likely only hasten the regime's end due to outside intervention.
The primary chemical weapons in the regime's arsenal are believed to be sarin, VX, tabun and mustard gas. A Stratfor source has indicated that the regime has around 650 metric tons of sarin, 200 metric tons of mustard gas and a much smaller stockpile of VX. Another Stratfor source said the Syrian missile and chemical command structure has changed twice since March 2011, but remains under the direct control of al Assad and the head of the national security council, Gen. Ali Mamluk.Before the conflict, the Syrian chemical warfare network was spread across the country. Several major storage and production sites were believed to be located near Homs, Hama, Eastern Damascus, Aleppo, Latakia and Palmyra. An additional 45-50 smaller facilities were spread out across the country, and Syria had the capacity to produce a few hundred metric tons of chemical agents per year. But a Stratfor source notes that the regime has ceased all production and has relocated the bulk of the storage facilities to the coast.
In terms of delivering the weapons, al Assad's forces have several options. The weapons can be deployed from artillery, ballistic missiles and aircraft. But all of these delivery methods have different constraints.
Syria has a large inventory of mortar, self-propelled and towed tube artillery, as well as rocket artillery. Most of these weapons could be used to stage a chemical weapons attack. However, the regime's artillery is widely dispersed around Syria, and a number of these weapons are in besieged bases in the north and east that are cut off from the regime's chemical weapons network.
The regime could also deliver chemical weapons using ballistic missiles. Estimates vary considerably, but the Syrian military is believed to operate about 200 relatively short-ranged SS-21 ballistic missiles with around 20 transporter erector launchers, as well as some 200 to 300 Scud-Bs and Scud-Cs with around 50 associated transporter erector launchers. The Syrian regime also operates a limited number of Scud-Ds with a range of up to 700 kilometers (435 miles). Syrian ballistic missiles are liquid-fueled, therefore requiring more time to fuel and prepare than solid-fueled missiles.
The Syrian air force has been considerably weakened by 21 months of war. Attrition rates are high due to accidents and enemy action, and maintenance levels are mediocre at best, resulting in the grounding of several aircraft. However, the Syrian regime can still muster a fixed-wing force that can be used to deliver chemical attacks with some 50 Mig-23BN fighter-bombers and about 20 Su-24 and 60 Su-22 ground attack aircraft. A large percentage of these aircraft are not in flying condition, but a considerable number are still serviceable.
Environmental Limiting Factors
While Syria has said it would not use chemical weapons against the rebels, Damascus has not ruled out deploying them against what it has called "external aggression." Even if the Syrian regime or forces on the ground decide to use these weapons, they will face major obstacles.
Chemical weapons require very specific weather and geographical conditions to be as efficient as possible. Cool, dry and still conditions in low bowl-like geographic areas provide the best chance for these chemicals to linger long enough to create casualties or provide area denial. Most of these agents are heavier than air and flow downhill.
Highly built-up urban areas actually protect targets from 95 percent of the chemical substances in an attack. Air conditioned buildings have positive air pressure and can prevent the agent from coming in, except for the air conditioner intake itself, but again the gases, aerosols or liquids disperse low to the ground and many intakes are on higher floors. Therefore, using chemical weapons in an urban area would yield few casualties relative to the amount used (it would be inefficient) and would be most useful for its psychological impact and as a temporary area denial measure. The ideal target for these types of weapons would be personnel in the open in a valley or trench-like geographic feature when weather conditions were cool, dry and still, such as in the early morning. High winds, humidity and heat dramatically shorten the time these substances stay concentrated in one area, which can also prevent or seriously degrade their effectiveness.
The ideal method of employment depends on the type of chemical weapons, which can generally be split between gases and aerosols or liquids. For gases, maintaining concentration is the key. They can be deployed at ground level or just above ground level using mortars, artillery, bombs or scuds. To achieve the maximum impact of a gas weapon, the targeted area must be filled, so multiple munitions must be dropped over time. This method is best suited for specific smaller areas, such as a trench system, bunker complex or small valley.
Aerosols and liquids are best employed at about 30-60 meters (100-200 feet) above ground level, blanketing the target area. These tend to be the deadlier or more efficient weapons, with more lethality by volume, and would be more realistic for medium to large targets. It is difficult to achieve the correct concentration of these substances. For example, about 3.8 liters (1 gallon) of VX should have the desired effect over 10 square kilometers if distributed evenly at the proper altitude. Accomplishing this with most ordnance is hard because it requires very complicated shots using precise fire directions and control or perfectly coordinated bombing runs. It also requires technologically advanced airburst cluster munitions. Syria is not believed to have this capability, but it is suspected to have clusters that can deploy chemicals at ground level.
Any ground or airbursting weapon that relies on an explosion for dispersal is already immediately destroying one- to two-thirds of the chemical substance. This means that 3.8 liters of VX is really only effective over 3-6 square kilometers. A limited number of inaccurate Scuds that rely on explosive dispersal are tactically useless in blanketing or saturating a given target with chemical weapons. The most effective way to employ aerosol or liquid chemical weapons is to drop them from slow, low-flying aircraft. This maximizes the efficiency of the chemical and is the best way to guarantee even and consistent saturation. The major drawbacks are obtaining planes that can perform this task with such dangerous, caustic chemicals and their susceptibility to air defense and ground fire since they fly at such low altitudes and air speeds.
For Syria, chemical weapons are dangerous to handle, relatively inefficient, require a huge amount of resources and are difficult to employ. In an operational sense, Syria would be hard pressed to make significant reversals on the battlefield with chemical weapons. They serve best as a deterrent or negotiation tool. If used, their greatest impact would be psychological, but they would also likely guarantee an international response that would negate any positive operational result.