Here's what happens when US Navy special operators go up against dolphins trained to keep them out of sensitive bases

• The US Navy has been training dolphins and sea lions to detect undersea threats since the 1960s.
• Over the years, the Navy has put those animals up against its most skilled human operators.

At the height of the Cold War, the US Navy turned to an unlikely source to protect its prized warships: dolphins and sea lions.

Beginning in the 1960s, the Navy implemented the Marine Mammal Program to defend ports and the important ships berthed there, especially nuclear-powered aircraft carriers and nuclear-powered ballistic-missile submarines, both of which are key to US power-projection and deterrence.

The program tested out a number of animals but found dolphins and sea lions to be the best suited for the mission. Their biological sonars enable them to detect things that electronic sonar might miss, such as enemy mines or lost equipment, and sea lions have sensitive hearing and acute eyesight that allows them to monitor the murkiest water for threats like enemy divers.

To track the dolphin underwater, the handler will attach a "pinger" device on the pectoral fin of the dolphin that will show the mammal's position. If the dolphin detects something, it will either attack it or surface to alert the handlers, who roam the surrounding waters in small boats.

The Navy has deployed its dolphins in war zones, such as Vietnam, and to hot spots, like the Persian Gulf, to guard against sea mines and intruders.

The US military wasn't the only one using dolphins and sea lions to protect its warships and ports. The Soviet military and its Russian successor also employ mammals for maritime security.

In order to find ways to defeat Soviet dolphins and sea lions and to ensure its own mammals were effective, the Navy turned to an elite human force: US Navy SEALs.

'Very real and very scary'

As the US military's prime maritime special-operations forces, Navy SEALs spend a lot of time in the water. The elite frogmen of US Naval Special Warfare Command are proficient in maritime insertion and an array of special-operations missions.

The Navy will often task SEALs to "attack" its most prized warships while they are in port to determine "if their force protection plan is functioning," and mammals and their handlers will play defense and try to "kill" or capture the "enemy" combat swimmers, a former Navy SEAL officer told Insider.

"This is good training for us because we might be called one day to place a limpet mine on an actual enemy ship," the former SEAL officer said, speaking on the condition of anonymity because they still work with the US government.

It is also good training for the ships and sailors of "Big Navy, because they are tasked with defending some of our military most valuable assets," said the former frogman, calling it "a win-win situation."

"It's scary when you're in the dark, cold water and you know that there is a huge dolphin somewhere out there. It's definitely a gut-check," the former frogman added.

The former SEAL said that it is hard to determine the effectiveness of dolphins and sea lions as military assets in actual wartime conditions. Technologies continue to evolve and emerge, and a way to "circumvent or neutralize" the mammals could arrive before any conflict with China or Russia breaks out.

The Navy's marine mammals have another role, and it's not one directed against enemy forces. During training, "those mammals were very real and very scary," the former frogman said.

Candidates in the Basic Underwater Demolition/SEAL course — a notoriously tough, and sometimes fatal, assessment that has attracted increased scrutiny for its brutality — have to complete several open-water swims in the Pacific Ocean.

During the swims, which can be as long as 5 miles, the candidates and their swim buddies are alone in the ocean.

BUD/S course instructors "have a sadistic tendency to scare the shit out of students before open-water swims," the former Navy SEAL officer said. "They will make us watch 'Shark Week' or tell us horror stories about killer dolphins and humongous sea lions that escaped from the Navy's pens and are swimming around looking for their next prey."

Into the future

Should a war with China or Russia break out, US special operators would be called upon to tackle conventional threats in support of other US forces, and they might encounter militarized mammals.

Russia's and China's navies would both pose a threat to the US military, but the Chinese Navy — the largest in the world — would be the more serious challenge because the conflict would mainly take place in vast ocean and coastal areas of the Indo-Pacific region.

US special-operations forces would be tasked with trying to disrupt, delay, or destroy Russian and Chinese ships in their ports. Navy SEALs, as the US's primary naval special-operations unit, would take the lead in any underwater special-operations mission against Chinese warships.

If the Chinese military employs dolphins or other mammals in force-protection roles, then US Navy SEALs might finally put their skills to the test against the real thing.

Stavros Atlamazoglou is a defense journalist specializing in special operations, a Hellenic Army veteran (national service with the 575th Marine Battalion and Army HQ), and a Johns Hopkins University graduate. He is working toward a master's degree in strategy and cybersecurity at Johns Hopkins' School of Advanced International Studies.