The US Navy is reportedly planning to replace its last military dolphins with robots.

In an exclusive interview with BBC Future, the navy said it would replace its highly trained pod of sea mammals with cheaper electronic alternatives.

The Navy has used dolphins in missions to help locate and even destroy mines at sea for more than 50 years.

The program was started in 1960, and also used sea lions, sharks and 16 other species. Bottlenose dolphins were chosen because of their sonar, high intelligence and underwater vision.

Now the practice will be phased out from 2017, because a new line of robotic mine hunters is cheaper and more effective, said Captain Frank Linkous, head of the US Navy’s Mine Warfare Branch.

The new generation of 7-metre-long underwater vehicles were first unveiled in April, and will be slowly phased in when they are ready.

BBC Future has the full story at its website (not accessible in the UK).

The Navy has always said that it treats its military animals with utmost care, and likens their use to that of security patrol dogs, whose sense of smell is superior to humans and many machines.

It has been criticised in the past, particularly. by animal rights groups, but says it is subject to the same laws and regulations as any organisation.

The service says on its website: "Just as the dog's keen sense of smell makes it ideal for detecting land mines, the U.S. Navy has found that the biological sonar of dolphins, called echolocation, makes them uniquely effective at locating sea mines so they can be avoided or removed."

It adds that rumours about the Navy deploying animals as offensive weapons are completely false.

"The Navy does not now train, nor has it ever trained, its marine mammals to harm or injure humans in any fashion or to carry weapons to destroy ships.

A popular movie in 1973 ("The Day of the Dolphin") and a number of charges and claims by animal rights organizations have resulted in theories and sometimes actual beliefs that Navy dolphins are assigned attack missions. This is absolutely false.

Since dolphins cannot discern the difference between enemy and friendly vessels, or enemy and friendly divers and swimmers, it would not be wise to give that kind of decision authority to an animal."