The dolphins in the US Navy

One of the strangest stories to emerge from the ruins of Hurricane Katrina is a tale of military-trained dolphins on the loose in the Gulf of Mexico. Whether they were whistling the Batman theme is not known.

The animals were reportedly being used by the US Navy to detect stray torpedoes and mines, and were controlled using signals transmitted to a neck harness. It is possible some were armed with toxic darts tied to their backs to immobilise terrorists or enemy agents.

"If divers or windsurfers are mistaken for a spy or suicide bomber, they could fire," warned an accident investigator close to the US Government's marine fisheries service.

Elsewhere in the dolphin world, a study to be published later this month reveals they can be trained to respond to music - and even reproduce the simple two-note theme from the 1960s TV programme about the Caped Crusader.

The Louisiana dolphins were apparently kept in training ponds close to Lake Pontchartrain, whose floodwaters helped to devastate New Orleans. The possibility that they escaped into the ocean surfaced after a separate group of "civilian" dolphins disappeared from a commercial dolphinarium on the Mississippi coast during the hurricane.

Eight were recovered alive with the help of the Navy. However, the dolphins were not returned to their owners until the authorities had a close look at them, sparking fears that some military dolphins had also escaped during the hurricane. The US Navy refused to comment.

Dolphins have been used by the American and Russian armed forces since the 1950s. The US Navy originally hoped to observe the dolphins' locomotive and sensory systems to improve the design of undersea weapons. They also carried out a range of classified experiments to study the uncanny ability of dolphins to find and retrieve objects from the seabed. It soon became apparent that dolphins were much better at this than human divers. It was also clear they were intelligent, capable of learning tasks quickly.

To teach a dolphin new tricks, scientists had to find a way of communicating with them. Unlike humans, dolphins have two forms of speech. One is a medley of whistles that they use to communicate with one another; the second a series of acoustic clicks used to locate food.

The clicks are more or less inaudible to the human ear and are used to find prey in murky water by bouncing high-frequency sound off them.

The instant of time between the emission of the pulse and the receipt of its echo tells the dolphin how far away the object is. And by emitting a stream of repeated clicks, the dolphin can also gauge the object's direction and speed.

Dolphins studied in Cardigan Bay off the coast of Wales could detect and then catch large fish from up to 72m away.

The principle of echo-location is the same as sonar, which we humans learned from another animal, the bat.

A dolphin's mind is therefore like a ship's sonar, gathering sufficient information about the size and speed of an enemy object to shoot it down with lethal accuracy.

Their ability to detect and monitor an object is thought to take place at an unconscious level, much as we see things. After all, how many of us could explain exactly how we know a road sign is roughly 30m away?

Scientists learned how to communicate with dolphins using an instrument called a hydrophone, an underwater sound projector which can deliver high-pitched sounds audible to the animals.

They learned that dolphins could be trained to recognise commands. They also found that the dolphins were able to mimic sounds and rhythms relayed through the hydrophone.

Studies soon to be presented at a meeting of the Acoustical Society of America will reveal that dolphins can even be trained to respond to music. One has learned to whistle the two-note theme from Batman, one short, the other long: "Bat-maaaan".

Appropriately, perhaps, it learned to produce the tune when presented with a Batman doll, for which it received the usual reward for cetacean intelligence - a fish.

The singing dolphin has broken one of the barriers that seemed to have set humans apart from the rest of the animal kingdom.

Gordon Bauer, associate professor at the New College of Florida, says: "This is the first report of a non-human mammal being able to discriminate rhythmic patterns." However, Bauer doubts whether dolphins have any sense of what we regard as music. "I think music is a human construct," he commented to the US cable channel, Discovery News.

"I doubt that it has pertinence to animals, but the elements of music, such as pitch, time, timbre and rhythm, may be incorporated into animal communication."

With intelligence added to unusual physical gifts, it was only a matter of time before captive dolphins were drafted into the wholly human preoccupation with security and warfare. From the 1960s, the US Navy is known to have employed up to 240 dolphins, as well as beluga whales, killer whales and sea-lions.

The work was conducted in secrecy but details emerged in 1988 when trainers who worked with Navy dolphins went public.

One dolphin known as Tuf Guy was trained to carry tools and messages to an undersea base called Sealab II, and could undertake tasks that were physically impossible for a human diver.

Dolphins were on active service before the first Gulf War, where they were mainly used for mine detection. More sinister was the use of dolphins in a "swimmer nullification program", where a long hypodermic needle was fastened to a dolphin's beak to fire a bullet of carbonic acid into an enemy frogman.

The US Navy has even reportedly used dolphins to patrol and guard Trident submarines in harbour - though once they had had their fill of fish they were apt to wander off duty.

With the Russians and Americans using dolphins there was, for a while, the science-fiction prospect of "dolphin wars", in which one lot carried electronic counter-measures to jam the sonar of the other.

Fortunately with the ending of the Cold War, the prospect of rival dolphins attacking one another has receded.

Are "killer dolphins" on the loose off the Mississippi coast? And are they a danger to divers and surfers? This is not the first time military-trained dolphins have escaped from their human masters. Up to 20 per cent of Navy dolphins are said to escape each year.

Do they soon forget about mines and torpedoes and refocus their echo-location towards catching fish and finding a mate? One escaped dolphin, called Dolly, later turned up on the Florida coast where she befriended a local family. Tamer than usual, she showed an impressive ability to retrieve and return coins from the water. In fact, she sounds more useful than Robin.

- INDEPENDENT