An Atlantic bottlenose dolphin named Tanner is shown during a demonstration at the Dolphin Research Center on Grassy Key in Marathon, Fla. (AP Photo/Wilfredo Lee)

Russia’s military is looking for a few good dolphins to join its navy – five, to be exact, with perfect teeth, average length and a willingness to “display motor activity.”

That’s according to a Defense Ministry tender that was published online this week. It offered about $24,000 to a broker who could supply three male and two female bottlenose dolphins, each about eight feet long, for the service of the Russian state.

The notice, which was described by the state-run TASS news agency before it was apparently taken down, did not indicate what military duty the dolphins would be expected to perform, nor why they need good teeth. But it rekindled speculation that the Russian navy is reviving the combat dolphin units that served as Soviet spies, investigators, rescuers – and possibly even assassins – during the Cold War.

Those dolphins were based in Sevastopol, on the Crimean Peninsula, during the Soviet era. They were absorbed by Ukraine after the collapse of the Soviet Union, and in 2000, the BBC reported that the animals, which had been moved to a “private dolphinarium to perform for tourists,” were being sold to Iran because its handler could no longer feed them.

Ukraine resurrected the dolphin military training program in 2012, according to the Guardian. But after Russia annexed Crimea in 2014, it also took control of the military aquarium and the dolphins, despite Ukrainian objections.

That same year, an anonymous source told the state news agency RIA Novosti that the Russian military was again training flippered fighters, which the Defense Ministry denied. (A Ukrainian military spokesman pooh-poohed the whole matter at the time, telling The Washington Post that “dolphins are not a military asset.”)

Whatever the case, the recruits will have a pretty fierce legacy to live up to. Dolphins’ fantastic sonar skill, or echolocation, make them excellent at detecting mines and sea vessels, locating lost divers and swimmers, and detecting enemy activity on the sea, shore and ships. The U.S. Navy agrees: It has used dolphins, as well as sea lions, since the 1960s.

But the Soviet dolphin secret agents were also trained as killers, according to some accounts. Viktor Baranets, a retired Russian colonel, told the Guardian this week that they planted explosive devices on enemy ships. The dolphins’ trainer told the BBC in 2000 that the animals were fitted with harpoons that they used to stab enemy swimmers and carried out kamikaze attacks on foreign vessels.

“The dolphins could allegedly distinguish foreign and Soviet submarines by the sound of their propeller,” the BBC wrote.

Doug Cartlidge, a former dolphin trainer, told Wired in 2007 that he had visited the Crimea dolphins after they were decommissioned. He said he was told that they were sometimes armed with needles connected to carbon dioxide cylinders, a poke from which could be lethal, and that they’d learned to parachute out of helicopters.

[What’s up with tough guy Vladimir Putin’s love for cute animals?]

The U.S. Navy started the dolphin arms race in the late 1950s when it began studying marine mammals’ hydrodynamic swimming skills for help in designing better torpedoes and subs. Then Navy officials realized that animals, particularly bottlenose dolphins and sea lions, could help divers themselves.

Dolphins have biological sonar, and sea lions have strong underwater vision and excellent hearing. Both can dive deep without getting decompression sickness, and they’re fast. They are also “highly reliable, adaptable and trainable marine animals,” according to the U.S. Navy Marine Mammal Program, which trains them in San Diego.

Dolphins defended America during the Vietnam and Persian Gulf wars. Today, the Navy says, its dolphin and sea lion recruits protect ports and Navy equipment from attack, locate sea mines and can mark and retrieve objects undersea. One shallow-water sea lion force is trained to attach clamps to enemy swimmers’ or divers’ legs, allowing American sailors to reel in foes like fish.

“One sea lion, two handlers and a rubber boat searching for objects on the ocean floor can effectively replace a full-sized naval vessel and its crew, a group of human divers, and the doctors and machinery necessary to support the divers operating onboard the vessel,” a program website says.

The U.S. Navy has long denied that its dolphins and sea lions are or were ever used to attack, though rumors persist.

“Since dolphins cannot discern the difference between enemy and friendly vessels, or enemy and friendly divers and swimmers,” the Navy says on the marine mammal program’s website, “it would not be wise to give that kind of decision authority to an animal.”

Tell that to the Russians.

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