Nuclear Doctrine has appeared frusty and irrelevant in the last couple of decades but I thought I'd dust off the information. If Syria uses chemical weapons against the US or US assets the US will not retaliate with nuclear weapons, however if Syria attacks British troops we will. The US has a started doctrine of no first use against NPT signatories (of which the Syrians are). Britain has no such compunction and Geoff Hoon is on record saying the use of chemical weapons against British troops will necessitate the use of nuclear weapons in retaliation. While we aren't getting directly involved in this one the Syrians should think twice about lobbing something at the quite close SBAs. It would be an interesting exercise trying to launch a 2-3 trident missiles - i.e. first having to warn Russia, China, France and the US as not to trigger cause an automatic response.