Syria crisis: How could US target chemical weapons?
The US is pushing for military action in Syria in response to a suspected chemical weapons attack. But can President Barack Obama target the country's chemical arsenal?
Speaking at the end of last month, he set out clearly the goal of any US military action against Syria.
Its purpose, he explained, would be "to hold the Assad regime accountable for their use of chemical weapons, [to] deter this kind of behaviour, and to degrade their capacity to carry it out".
Now Mr Obama is seeking Congressional approval for any strike, but many questions remain, not least the scale and scope of any attack and the extent to which it might target chemical weapons facilities directly.
On the face of things this is probably highly unlikely.
Some elements of the Syrian chemical weapons complex may be buried underground but large parts of it can easily be seen on satellite images.
Much of it is reasonably close to populated areas - and this is the problem. Attacking such sites with regular explosive bombs might well wreak considerable damage but it could also open up chemical weapons stocks to the air, disperse them over a large area, and potentially cause large numbers of civilian casualties.
For years the United States has been seeking to develop warheads that could be used to destroy chemical weapons stocks without the dangers described above.
So-called "Agent Defeat Weapons" are probably available to US commanders. They operate in various ways but the essential feature is intense heat - it is like a super-incendiary bomb - that destroys the chemical or biological agent in situ.
The temperatures needed are dramatically high, within the range of 1,200C to over 1,500C.
Though some experts suggest that these highest temperatures would be required to destroy biological material, chemical weapons like the nerve agent VX for example would be destroyed at the lower end of the range.
The exact status of these munitions in the US arsenal is uncertain. One system is known as "crash pad" - a high-temperature incendiary weapon. Another is called the Passive Attack Weapon or PAW which depends upon the kinetic energy of a mass of steel or tungsten rods to produce the necessary heat.
Nonetheless the scale of the Syrian facilities and their proximity to civilians may convince US planners to avoid targeting CW sites altogether. There may perhaps be elements of these installations that can be hit - for example, power supplies. But a safer option might be to target other aspects of Syria's capability, especially delivery systems.
This would mean striking artillery and rocket systems; aircraft; maybe even missile production facilities. Headquarters and other buildings associated with units linked to the chemical weapons programme could also be struck.
But here there is another problem for President Obama. Many of these potential targets - artillery and aircraft for example - are a key element of President Assad's superiority over the rebels.
If you damage these assets badly enough you risk significantly altering the military balance on the ground in favour of the rebels. And this is something that Mr Obama has apparently ruled out. Maybe he is changing his mind as he seeks to win over a sceptical Congress.
For all of the senior figures on Capitol Hill who want to see more resolute action against the Assad regime there are those who want no strikes at all or very limited military action.
Mr Obama has a doubly difficult task. First to sell the idea of a punitive strike to politicians with a variety of views at home; but then to calibrate the scale and scope of the attack itself, if it goes ahead, to ensure that it delivers the necessary warning while not totally overturning the situation on the ground.