While the dolphins' precise mission - like much of the Navy's marine mammal program - remains classified, the service previously has acknowledged the existence of the program, which recruits dolphins, seals and whales for various military missions.
The highly trained bottle-nosed dolphins will be used to find, but not detonate, the spiked contact mines that Iran has been planting in regional waters since U.S. Navy warships began escorting Kuwaiti tankers through the gulf in July, according to defense officials who declined to be identified.
The flippered force, part of the Navy's 25-year-old marine mammal program, has been trained to detect mines as well as retrieve objects from the sea bottom and rescue military divers.
About 150 Navy personnel train the dolphins at bases in Hawaii, California and Florida. Two of the units assigned dolphin-training roles are described by the Navy as "explosive ordnance disposal mobile units," suggesting a mine- clearing mission.
"There's a number of people with them in the gulf looking after their health and welfare," a defense spokesman said, insisting that the dolphins would play no role in disarming mines once they were located. The U.S. military "has never trained, nor does it intend to train, marine mammals to perform a task that could result in their intentional injury or death," he said.
The Navy - which will spend $5.4 million this year for its Advanced Marine Biological Systems project to train marine mammals - has captured 240 dolphins since 1962, and some have been born in captivity.
This year, the Pentagon received congressional permission to capture up to 25 marine mammals annually for "national defense purposes." Congressional assent is needed because the capture of dolphins is restricted under the 1972 Marine Mammal Protection Act.
In tests in 1985 in South Carolina, dolphins - using their amazing power of echo-location like a sonar system - detected mines 80 percent of the time, a success rate far superior to that of Navy hardware, a defense official said.
According to one 1980 report, Navy dolphins were capable of detecting a submerged three-inch steel sphere located more than 120 yards away - a distance longer than a football field. The Iranian mines are about three feet in diameter.
A 1967 Navy study said a blindfolded dolphin could distinguish a copper plate from among aluminum ones by using echo-location and discerning the difference in the sounds reflected by the metals.
"It is clear the use of dolphins has entered contemporary naval tactical thought," Cmdr. Douglas Burnett said in a 1981 article in Proceedings, the journal of the U.S. Naval Institute. "Their potential in mine warfare and in- shore anti-submarine warfare is promising."
The Pentagon spokesman said the dolphins' role in the gulf would not be publicized further.
"They don't pose a threat to the Iranians - we have no kamikaze animals," he said. "They're there for defensive purposes."