BAGHDAD — Air raid sirens are sounding over Baghdad as the Iraqi capital braces for a possible air assault from allied troops.
Anti-aircraft guns are firing into the sky.
Earlier in the day, eight American B-52 bombers took off from Fairford Airbase in Britain -- a sign that major nighttime air strikes could be hours away.
One U.S. official involved in military planning said the B-52s had been scrambled en masse and the air strikes would be bigger than anything seen thus far in the conflict.
On Wednesday, six other B-52s left Fairford to be pre-positioned closer to Iraq.
The 14 heavy, high-altitude bombers -- used for bombing campaigns during Vietnam -- are expected to be a big part of the coalition's "shock and awe" campaign. Each B-52 can carry 12 Joint Direct Attack Munitions (JDAMs), eight Conventional Air Launched Cruise Missiles (CALCMs) inside and another 12 externally, or a variety of other non-precision bombs."