The research builds on experimental work to control animals by implanting tiny electrodes in their brain, which are then stimulated to induce a behavioural response.

"The Pentagon hopes to exploit sharks' natural ability to glide quietly through the water, sense delicate electrical gradients and follow chemical trails," says the report, carried in next Saturday's New Scientist.

"By remotely guiding the sharks' movements they hope to transform the animals into stealth spies, perhaps capable of following vessels without being spotted."

The unusual project is being funded by the Pentagon's Defense Advanced Research Projects Agency (DARPA), which pioneered the Internet as a platform for robust communications.

Scientists involved in the scheme presented their work last week at a meeting on Ocean Sciences in Honolulu, Hawaii, according to the report.

A team at Boston University have implanted electrodes into the brain of a spiny dogfish in a shallow tank.

Brain implants

"By remotely guiding the sharks' movements they hope to transform the animals into stealth spies, perhaps capable of following vessels without being spotted"

New Scientist

The implants, controlled by a small radio transmitter, stimulate either the right or left side of a brain area dedicated to smell, causing the fish to flick around in that direction in response to the signal.

The next step will be to take this device outside the laboratory. Blue sharks implanted with the gadget are to be released off the coast of Florida.

As radio signals will not penetrate the sea, communications with the fish will be made through US Navy acoustic towers capable of sending sonar signals to a shark up to 300 kilometers (187 miles) away.

Other DARPA-funded researchers are working on using implants to record brain activity in sharks in order to understand which neurons are fired by scents, electrical or magnetic fields.

These signals help the fish to navigate and offer the reward of food, and could thus in theory be manipulated for surveillance work.

New Scientist says the DARPA work is controversial, but also points out that work with animal implants also has a potential benefit for medicine.

Understanding more about the brain's electrical signals could one day result in implants to control a prosthetic limb to overcome paralysis.