Tomahawk cruise missiles are likely to be launched at night against hundreds of Syrian targets, including some of President Bashar al-Assad's elite military units, if the US and allies launch a military strike in retaliation for the use of chemical weapons.
"I'm thinking a pretty significant initial wave" of several hundred Tomahawks "and an assessment period and maybe a second wave if we don't think we accomplished the destruction we wanted to," said Jeffrey White, a former Defence Intelligence Agency analyst who is now a defence fellow with the Washington Institute for Near East Policy.
However, President Barack Obama said on Wednesday he had not yet signed off on a plan to strike Syria, although his administration is working with allies including the UK and France, which also have aircraft and ships armed with cruise missiles, to reach agreement on limited action against Syria after concluding that Assad's regime used chemical weapons against civilians.
Political uproar in London, meanwhile, cast doubt on whether Britain will join American military action to punish President Bashar al-Assad’s regime for a chemical weapons attack, should the response take place before next week.
A limited strike could be directed at the headquarters, facilities and depots of Assad's most elite units, the Republican Guard and the 4th Armoured Division, which some US officials think are most likely to have mounted the reported chemical weapons attack last week that opposition forces say killed about 1,300 people.
Video: UN investigates suspected chemical attack in Syria
"There are some target sets that would be important to meet the goals of a limited operation," such as the key units that "support the regime and have been bombarding civilians," White said in an interview.
A team of UN inspectors on Wednesday pressed on with its hazardous work in Damascus, testing victims of the alleged poison gas attack, which killed hundreds of people last week and threatens to draw reluctant Western states into a vicious civil war.
Obama, who has warned that the use of chemical weapons in Syria would cross a US “red line,” said Washington had definitively concluded that the Assad regime was to blame for last week’s attack.
A senior White House official said the administration will brief senior US lawmakers on Thursday about classified intelligence about the chemical attack.
Asked how close he was to ordering a US strike, expected to start with cruise missile raids, Obama told PBS NewsHour: “I have not made a decision.”
But he warned that US action would be designed to send a “shot across the bow” to convince Syria it had “better not do it again.”
A campaign extending beyond cruise missiles could add satellite-guided glide bombs dropped from Air Force F-15 or F-16 fighter jets or Navy F-18s that remain outside Syrian airspace. B-2 stealth bombers flying from their base in Missouri could drop bombs while penetrating Syria's dense air defences.
The US also could use remotely piloted aircraft, or drones, to collect intelligence, pinpoint convoys or other moving targets for cruise missile attacks or conduct their own strikes.
The introduction of ground troops isn't being considered, nor is the imposition of a no-fly zone over Syria, according to a US official who asked for anonymity to discuss internal deliberations.
Brigadier General Mustapha al-Sheikh, who was among the first Syrian officers to defect from the army, said any military strike by the US and allies is likely to be modest.
"I expect a couple of strikes inside Damascus and the bulk in the provinces so there won't be a political vacuum inside Damascus," he said in an interview from Syria. "This doesn't lead to toppling the regime."
No matter how carefully targeted, any military attack comes with risks, from accidental civilian deaths that could feed anti-American sentiment in the Middle East to an escalation of chemical or other warfare by Assad's regime.
"There is a risk that the regime could withstand limited strikes by dispersing assets," Army General Martin Dempsey, chairman of the Joint Chiefs of Staff, wrote in a July 19 letter to Michigan Democratic Senator Carl Levin, chairman of the Senate Armed Services Committee. "Retaliatory attacks are also possible, and there is a probability for collateral damage impacting civilians and foreigners inside the country."