Each carrier has about 70 F-14 and F-18 aircraft and is escorted by about a dozen supporting vessels.
Together they also carry 6000 Marines.
The amphibious assault ship USS Essex has also left its Japanese base accompanied by the nuclear-powered submarine USS Bremerton.
The Royal Navy aircraft carrier HMS Illustrious is stationed in the Gulf with 24 ships and two nuclear submarines.
An airbridge of KC-135 flying tankers has been established to help ferry about 100 aircraft, including B-1 and B-52 bombers from Barksdale and Robins Air Force Bases, to the Gulf and Britain's Indian Ocean territory of Diego Garcia.
They will work alongside fighter and bomber units already stationed in Kuwait, Oman, Saudi Arabia and Turkey, while a further 62 B-2 "stealth" bombers, based at Whiteman Air Force Base in Missouri, can strike at Afghanistan using inflight refuelling.
US attack helicopters are already stationed in Uzbekistan, north of Afghanistan, where they have been involved in joint military exercises.
The United States has maintained about 15,000 troops in the critical region since the Gulf War, but a further 2000 Marines left Camp LeJeune, North Carolina, at the weekend.
Once assembled, this force will be commanded by General Tommy Franks, successor to Gulf War commander General "Stormin' Norman" Schwarzkopf, from US Central Command in Tampa, Florida.
US officials are planning to combine the awesome firepower of this force with small covert operations to win a rare strategic victory in Afghanistan followed by an orderly withdrawal.
Any initial large-scale strikes are expected to be made by Tomahawk cruise missiles launched from US ships, the British nuclear submarine HMS Trafalgar and B-52 bombers flying from Diego Garcia.
The secret side of the military buildup, dubbed Operation Veritas in Britain, began within 24 hours of the attack on America.
Spy satellites were quickly flown over bin Laden's known mountain strongholds in Khost and eastern Kunar province, while American and British special forces units began rolling. Pakistani intelligence officials claim construction of the hideouts near Khost was funded by the CIA during the Afghan-Soviet War.
Two British SAS units left their Brize Norton airfield to join MI6 and CIA operatives already in northern Afghanistan, and the US 82nd Airborne and 101st Air Assault Division based themselves in Pakistan at Quetta, Dera Ismail and the Badeber base near Peshawar.
Deep penetration units of the US 160th Aviation Regiment "Nightstalkers", specialists in operating in difficult weather and terrain, are reported to be heading to Pakistan via Sicily with their Pave Hawk and Littlebird stealth helicopters.
American Halo (high altitude, low opening) paratroopers are also on standby. These units jump at night from up to 6100m, using oxygen, before opening their parachutes within a few hundred metres of the ground.
The SAS units are trained to operate within enemy territory for long-periods, while their American counterparts favour swift hit-and-run tactics using Black Hawk and Super Stallion helicopters.
The United States is also wheeling out its diplomatic and economic guns.
Legislation is being introduced to ban access to American markets for any people, groups or banks that do not meet US approval and the Treasury has already begun closing bank accounts associated with terrorist fundraising.
American intelligence agencies aim eventually to be able to monitor and control the worldwide flow of cash through the banking system.
Diplomatic feelers are also being extended towards Iran with the aim of securing its cooperation, or at least non-interference, in any battle against bin Laden and the Taleban.
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America
