Aircraft carriers and guided missile destroyers moved into the waters near New York and Washington after President George Bush placed the US military on its highest alert status.
‘‘We have been attacked like we haven’t since Pearl Harbour,’’ said Admiral Robert Natter, commander of the US Atlantic Fleet in Norfolk, Virginia.
The ships Natter sent to stand off the East Coast included the carrier George Washington, which was in position off the coast of New York City this morning.
Another carrier, the John F Kennedy, was heading to New York, an Atlantic Fleet spokesman said.
Each has a crew of 2,500 to 3,000 sailors, and the JFK’s airwing has about 1,500 sailors.
The Comfort, a hospital ship in Baltimore harbour, also was made available.
Also deployed were amphibious ships, guided missile cruisers and guided missile destroyers that are capable of responding to threats from the air and sea. The amphibious ships were carrying Marines and sailors to provide security, surgical teams and limited hospital bed capacity.
The US Pacific Fleet had a number of ships under way in the Pacific Ocean, a Navy official at Pearl Harbour said.
The John C Stennis aircraft carrier was steaming off San Diego and two guided missile cruisers, three guided missile destroyers and five guided missile frigates were at sea in the eastern Pacific, he said.
The Russell guided missile destroyer, the Navy rescue ship Salvor and the Navy oiler Yukon were off Hawaii.
Military aircraft were seen patrolling the skies above the capital.
Elsewhere in the country, fighters, airborne radar and refuelling planes were scrambled, according to an Air National Guard spokesman.
The North American Aerospace Defence Command also was on its highest alert status.
‘‘We have all of our air sovereignty aircraft fighters, surveillance and other support aircraft ready to respond,’’ NORAD said in a statement.
The US portion of the St Lawrence Seaway also was closed, said Lynn Duerod, spokeswoman for the Army Corps of Engineers in Detroit.