The U.S. military presence in Kuwait, Bahrain, Qatar, Oman and the United Arab Emirates has been growing since the Persian Gulf war in 1991. But the growth has accelerated as U.S. forces launched military action against the Taliban and al-Qaida in Afghanistan and began preparing for a possible invasion of Iraq.
"When the balloon goes up, it will be all that much easier" as a result of these preparations, said retired Rear Adm. Richard H. Baker, a senior fellow at the Center for Defense Information, an independent research group.
The U.S. military expansion in these small gulf states helps fill a major strategic shortcoming exposed by the 1990 Iraqi invasion of Kuwait, when U.S. officials realized they had insufficient forces and equipment in the region to defend oil fields vital to Western economies.
It took weeks for U.S. forces to get into position to defend Saudi Arabia, the world's largest oil producer, and several months more to build up its offensive might to drive Iraqi troops from Kuwait.
The years after the gulf war also drove home to the Pentagon the acute political sensitivity of stationing U.S. forces on Saudi soil and of using the kingdom to launch offensive military operations against another Arab or Muslim country.
The warm attitude of successive Saudi monarchs toward the United States has drawn protests from dissidents, and the presence of U.S. troops in the land of the Islamic shrines at Mecca and Medina is a source of resentment for the powerful Wahhabi Muslim religious establishment. Exiled Saudi terrorist Osama bin Laden has cited the presence of U.S. troops on Saudi soil as the chief justification for his war against the United States.
U.S. analysts say Saudi Arabia will remain a crucial ally because the kingdom dwarfs the other gulf monarchies in size, population, wealth and influence in the Arab world and beyond.
"You can't bypass Saudi Arabia strategically," said Anthony H. Cordesman, a specialist in Middle East security at the Center for Strategic and International Studies in Washington.
The Saudis have recently held open the possibility of allowing the United States to use forces based in the kingdom for an attack on Iraq - provided the war is authorized by the United Nations. But some of the smaller gulf states have fewer inhibitions about openly cooperating with the United States.
But while rapidly modernizing, they have been slow to democratize, preferring instead to preserve the gulf tradition of consensus-building among tribal leaders. And the smaller gulf states aren't immune to the same anti-American fervor that makes the Saudi rulers nervous. But they don't share the Saudis' inhibitions about openly cooperating with the United States.
While the Pentagon won't give a breakdown by country, unofficial estimates say 10,000 U.S. military personnel are based in Kuwait, where the Central Command has its permanent regional Army headquarters.
Bahrain, which has a long-standing, but growing, relationship with the U.S. Navy, is host to the 5th Fleet and also serves as regional headquarters for the Marine Corps and for a force of Navy Seals.
The United States is using Al Udeid Air Base, which is outside Qatar's capital, Doha; it has a 15,000-foot runway, the longest in the gulf region. A command-and-control center at the base is loaded with sophisticated equipment rivaling that of the Prince Sultan base in Saudi Arabia, said Baker of the Center for Defense Information.
Oman is building a 14,000-foot runway and serves as a hub for U.S. airlift operations, according to the center, noting that the B-1 bomber force operating in the region is probably based in Oman.
The United States enjoys access to air and naval facilities in the United Arab Emirates, where stocks of U.S. military equipment are stored. The UAE has also agreed to permit the stationing of an Army brigade with 120 tanks, said Cordesman, the Middle East analyst.