The Tomahawk land-attack cruise missile, fired safely from a warship or submarine far away from the target, seems to be the best option to reduce the risk of “collateral damage”.
All the signs are that Chuck Hagel, US Defence Secretary, has put the Tomahawk at the top of his list of options for Mr. Obama. He has lined up four guided-missile destroyers, armed with Tomahawks, in the Mediterranean, with instructions to the warship commanders to be on the alert for an order from the White House.
Britain will have a Trafalgar class nuclear-powered submarine, also equipped with Tomahawks, to support such an operation. Each of the Arleigh Burke-class destroyers has at least 90 Tomahawks on board, giving a total of almost 400 missiles ready to launch if Mr Obama decided to go down the military route but restrict the mission to a single aim - to prevent or deter President Assad from using chemical weapons again.
The Tomahawk is guided by GPS to provide navigation precision, but the warhead contains only 454 kg of high explosives, a payload designed to damage, not destroy, its target. A full-scale air campaign, as in Kosovo, would necessitate taking out Syria's air defences - a challenge that General Dempsey appears keen to avoid. So the Tomahawk option rises to the fore. Targets could include chemical weapons storage and production sites, although there would be a risk of chemicals entering the atmosphere.