The deployment doubles the number of mine-hunting warships the U.S. 5th Fleet, which has headquarters in Bahrain, will have operating in the region, through which one-fifth of the world's oil supplies pass.
The U.S. Navy has identified the mine-hunters as the Avenger class USS Sentry, USS Devastator, USS Pioneer and USS Warrior out of San Diego.
These slow-moving 1,379-ton ships, all transported to the gulf aboard heavy-lift vessels, will join their forward-deployed sister ships USS Scout, USS Gladiator, USS Ardent and USS Dextrous.
The British navy also has four mine countermeasures vessels in the gulf.
The Americans plan to deploy at least four mine-sweeping MH-53E Sea Dragon helicopters to the gulf as well.
The Iranians have threatened to close the Strait of Hormuz, the only way in and out of the gulf, if its vital oil exports are cut off or if it is attacked.
They are reputed to have in excess of 5,000 mines, many of them advanced Russian-built variants that are hard to detect and disarm. They also have batteries of Chinese-designed cruise missiles along the waterway's eastern shore.
Iran's air force has strike aircraft, although these are largely outdated U.S.-built F-14 Tomcats bought during the days of the shah. They have some Russian-made MiG-29s as well.
If a shooting war does break out, the U.S. Central Command believes it's capable of destroying or seriously degrading Iran's forces within three weeks, U.S military sources say.
This would be achieved largely through air and sea strikes using aircraft and missiles, the sources say.
The Americans have two navy carrier battle groups in the region.
In April, the Pentagon deployed an unspecified number of Lockheed Martin F-22 Raptor strike jets, the most advanced operational fighter in the world, to Al-Dhafra airbase near Abu Dhabi, capital of the United Arab Emirates.
Al Dhafra is being used by U.S. Air Force KC-10 aerial tankers along with U.S. surveillance aircraft, including the venerable U-2 and the unmanned Global Hawk.
At about the same time, the Air Force deployed 20 upgraded F-15C Eagles of the 104th Fighter Wing of the Massachusetts Air National Guard to an undisclosed base in the Central Command area of operations.
Military sources say the Boeing F-15s are either at Al Dhafra or the large U.S. air base at Al Udaid in the Gulf emirate of Qatar. Al Udaid also houses Central Command's forward headquarters.
The F-22s and the 104th's F-15s are believed to have been training to operate together in the air-to-air fighting role, tasked with eliminating the Iranian air force's fighter squadrons.
"The Raptor-Eagle team has been honing special tactics for clearing the skies of Iranian fighters in the event of war," reported David Axe of Wired.com, which specializes in military weapons systems.
Axe noted that the "U.S. dogfighting armada" assembling in the Arab monarchies on the gulf's western shore that face Iran would likely operate in small groups, using silent electronic exchanges of data to "wipe out the antiquated but determined Iranian air force" with state-of-the-art missiles systems.
The U.S. air assets would provide a "significant dogfighting presence" in the gulf, Axe noted.
The F-22 has been deployed to the Pacific theater several times but has yet to make its combat debut since it was declared operational in 2005. But for all its vaunted combat capabilities, the aircraft's been plagued a serious flaw in its oxygen generating system that has caused some pilots to lose consciousness.
U.S. forces also have a heavy air component aboard the carrier battle groups headed by the USS Enterprise and the USS Abraham Lincoln in the region. Between them they can muster more than 100 combat F/A-18 Hornet and Super Hornet strike aircraft.
But former CIA officer Philip Giraldi has warned that U.S. Internal Look war games conducted in March indicated that the Navy "would have considerable problems dealing with Iranian offensive operations" in the narrow waters of the strait.
The games "revealed that there is a high probability that Americans vessels will be sunk, with considerable loss of life," Giraldi observed.