For decades, science fiction writers and futurologists have predicted a time when wars are fought at the push of a button and Terminator-like robo-soldiers fight in place of humans. While the rise of drone warfare suggests that vision may be starting to come true, it would seem that it will not be humans who are first in line to lose their military commission.

“We’re in a period of transition,” explains Captain Frank Linkous, head of the US Navy’s Mine Warfare Branch. After nearly 50 years, he says, the Navy plans to phase out its Sea Mammal Program and retire its pods of dolphins and sea lions that are currently used to help locate – and in some cases destroy – sea mines.

“In general, we’re looking to phase out that program beginning in fiscal year 2017,” says Linkous.

Swimming into their place is a new generation of robotic mine hunters, he says. But, the shift comes at a critical time. Earlier this year, Iran threatened to mine the Strait of Hormuz, shutting down the critical waterway to commerce. That threat prompted a renewed debate over investment in mine warfare technology, which many naval experts feel has been long neglected.

The difficulty of finding and clearing mines is why dolphins capabilities’ are so prized: their use of echolocation to spot objects is the biological equivalent of sonar, making them an ideal tool for hunting mines. "We've got dolphins," retired Admiral Tim Keating, who commanded the US 5th Fleet in Bahrain, told National Public Radio, when asked how the US might respond if Iran makes good on its threats.

Pensioned porpoise

These sea mammals have been a highly prized part of the US Navy ever since the 1960s, when military researchers began to try to understand the dolphin’s senses and capabilities. The rapid realisation that untethered dolphins could be trained to carry out tasks in open water, meant the research quickly evolved into a classified training programme, prompting rumours that the Navy was honing an elite cadre of killer dolphins. The project was eventually declassified in the early 1990s, and these days, it is out in the open (the dolphins are not used for killing anyone), with the Navy taking great pains to demonstrate its care for these sea creatures.

The Navy compares the dolphins to the critical role of bomb dogs being used in Afghanistan, and the dolphins are widely praised for their abilities. But it also makes clear the sea mammals’ purpose is to serve the military. In Pentagon parlance, the mammals are referred to as a “system”, similar to any other technology in its inventory. For example the Mk 4, Mod 0 (short for mark 4 and modification zero), is the designation for a dolphin that detects mines that lie near the bottom of the sea, and then neutralises it by attaching a charge and swimming away; the Mk 5 Mod 1, by contrast, is a sea lion that is used to help recover mines during naval exercises.

But that will soon change. In April, the Navy unveiled its plans for Knifefish, a torpedo-shaped, underwater robot that would roam the seas for up to 16 hours, looking for mines. The 7m- (20ft-) long unmanned underwater vehicle (UUV) is still in development, but should be ready by 2017, and will use sonar to hunt mines. “The Knifefish UUV is ultimately intended to be the replacement for the marine mammals,” Linkous says.

Of course, previous efforts to replace military service animals have proved hard, at least when it comes to dogs. For years, scientists have been trying to develop a chemical nose that mimics the capabilities of a canine, but still admit that when it comes to detecting explosives, dogs beat technology hands down.

Similarly, the Navy already admits there may still be some specialised missions where sea mammals are needed past 2017.

But what is driving the desire to replace dolphins and sea lions is not their capability, but cost. A dog might deploy with just a handler and food, but when the sea mammals are sent on long trips, they must be transported aboard naval vessels where they are kept in custom enclosures and accompanied by handlers and a portable veterinary clinic with staff.

The costs don’t end there: while a bomb dog typically goes to live with its handler when it retires, dolphins require specialised care. “The Navy is very humane about the way they treat these animals,” says Linkous. “Essentially, these animals have a pension – they are cared for the rest of their lives.”

Dive buddy

The sea mammals are a “fantastic system,” says Linkous, but robotic technology will be able to do much of what they can do only cheaper and easier. “Maybe not 100%, but fairly close,” he says.

And it’s not just dolphins that are being moved out of service by robots: the Navy is also hoping to at least reduce reliance on humans who perform dangerous bomb disposal missions, known as explosive ordnance disposal (EOD). The Navy has been moving quickly to rush new robotic technologies to the field, including an unmanned underwater vehicle, known as the Kingfish, and four unmanned surface vessels that the Navy originally bought for anti-submarine warfare, but are now being outfitted with sonar to hunt mines.

The Navy is also buying the German-made SeaFox mine hunting system, another robotic underwater vehicle that is guided by a fibre-optic cable and can be used to attach a charge to a mine. Right now, naval divers that are trained as explosive ordnance disposal technicians carry out many critical mine clearing tasks, but technology like the SeaFox will help reduce the number of dives these personnel have to make, according to Linkous.

“This is very much like the concept that EOD technicians have done on the ground in Afghanistan and Iraq: greater use of robotic systems to neutralise and destroy IEDs in the field,” Linkous says. “It’s the same concept.”

Does this mean that someday humans will go the same way as the sea mammal program? Probably not anytime soon, says Linkous. Divers can still do some things more effectively than robots.

“There’s an enduring role for EOD [technicians],” he says. “They just do it more quickly.”

If you would like to comment on this article or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.