But the Fifth Fleet compound itself looks like little more than a modern office park in a quiet neighborhood of Manama, the capital, whose piers occasionally host a warship but never a sustained presence of hulking vessels comparable to bases in, say, Norfolk, Va., or Yokosuka, Japan.
Day by day, the Fifth Fleet is at sea and in the air, across 2.5 million square miles of water.
In Manama, a city that is more open and socially welcoming to foreigners than those in much of the restrictive Arab world, American personnel live out in the community, and not in isolation.
And thus far, Navy officers are quick to point out, the street protests have given voice to a disenfranchised Shiite majority’s complaints about Bahrain’s leadership — but the United States has not been cast as a villain, despite six decades of close ties with the governing Sunni elite.
“We are monitoring what’s going on,” said Cmdr. Amy Derrick-Frost, the Fifth Fleet spokeswoman. “The protests and demonstrations are not against the United States or the United States military or anything of that nature.”
Military personnel, Defense Department civilians, contractors and their families — numbering about 6,100 in total — have been advised to avoid areas where the protests were taking place, but as of late Thursday there was no order to evacuate dependents.
“We do not have any information at this time that suggests that planned protests are likely to cause significant disruptions,” said Jennifer Stride, a spokeswoman for the Naval Support Activity, which oversees the military complex. “We will continue to monitor the situation.”
The Navy has had a presence in Bahrain since Franklin Roosevelt’s presidency, well before it took over a British army base east of Manama, in 1971, when the country achieved full independence.
The 100-acre naval base is in Juffair, a suburb six miles from Pearl Square in the center of the capital, where thousands of mostly Shiite protesters were attacked by security forces early Thursday morning.
Though the base is physically separated from its piers, Ms. Stride said there was “no concern” about being cut off if protests were to widen. “There are no demonstrations at all in the vicinity of the base or those piers,” she said.
The broad mission of the Fifth Fleet includes combat, counterterrorism, air support for the operations in Afghanistan and Iraq, antipiracy efforts and military exercises with regional allies, including Bahrain.
Much of the fleet’s time is spent watching Iran’s two navies — the more professional Iranian state fleet and the less predictable Revolutionary Guard navy that has harassed American warships in recent years.
The United States and Bahrain signed a 10-year defense pact in 1991 that includes American training of Bahraini forces; it was renewed in 2001, according to a Congressional Research Service report.
“Bahrain has few external security options other than relying on some degree of U.S. security guarantee,” said a study by the research service released last month. “The United States has designated Bahrain as a ‘major non-NATO ally,’ and it provides small amounts of security assistance to Bahrain.”
The Fifth Fleet’s area of responsibility includes waters that touch 20 countries along the Persian Gulf, the Red Sea, the Gulf of Oman and parts of the Indian Ocean. The area includes the Strait of Hormuz, the Suez Canal and the Strait of Bab el Mandeb at the southern tip of Yemen — all strategic passages for international shipping.
“As a longtime ally and home to the U.S. Navy’s Fifth Fleet, Bahrain is an important partner and the department is closely watching developments there,” said Col. David Lapan of the Marine Corps, a Pentagon spokesman. “We also call on all parties to exercise restraint and refrain from violence.”
Thom Shanker reported from Washington, and J. David Goodman from New York.