Sea Lions & Spies: Five Secrets About the US Navy’s Elite Swimmers


While much has been written about the friendly, smiling dolphins trained by the US Navy, little is known about the crucial role sea lions play in national security. SPYSCAPE looked into the job of these incredible marine mammals.

The US Navy with a sea lion
California sea lion Jack salutes his handler in Bahrain, 2014

1. Sea lions utilize superior eyesight and speed to accomplish their missions

Sea lions are capable of repetitive deep diving, can see in low light, and have underwater directional hearing so the US Navy uses sea lions to recover objects in harbors and open seas as well as to attach recovery lines to equipment on the ocean floor. They’re actually faster swimmers than human divers so the Navy also uses sea lions to recover important equipment and to help spot unauthorized divers. 

The Navy’s MK 5 sea lion team recovers test equipment fired from ships or dropped from planes into the ocean; the California sea lions can also locate and attach recovery hardware to underwater objects such as practice mines.

In its first successful recovery mission, an MK 5 sea lion recovered an ASROC (anti-submarine rocket) from a depth of 180 feet in 1970. Naval sea lions have also been trained to recover crash-test dummies from the sites of plane crashes. 

Sea Lions & Spies: Five Secrets About the US Navy’s Elite Swimmers

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While much has been written about the friendly, smiling dolphins trained by the US Navy, little is known about the crucial role sea lions play in national security. SPYSCAPE looked into the job of these incredible marine mammals.

The US Navy with a sea lion
California sea lion Jack salutes his handler in Bahrain, 2014

1. Sea lions utilize superior eyesight and speed to accomplish their missions

Sea lions are capable of repetitive deep diving, can see in low light, and have underwater directional hearing so the US Navy uses sea lions to recover objects in harbors and open seas as well as to attach recovery lines to equipment on the ocean floor. They’re actually faster swimmers than human divers so the Navy also uses sea lions to recover important equipment and to help spot unauthorized divers. 

The Navy’s MK 5 sea lion team recovers test equipment fired from ships or dropped from planes into the ocean; the California sea lions can also locate and attach recovery hardware to underwater objects such as practice mines.

In its first successful recovery mission, an MK 5 sea lion recovered an ASROC (anti-submarine rocket) from a depth of 180 feet in 1970. Naval sea lions have also been trained to recover crash-test dummies from the sites of plane crashes. 

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A sea lion and US Navy diver recovery expert

2. Sea lions can arrest you

The Navy doesn't train marine animals for attack missions - at least, not that we are aware of - but they do recruit the animals for defensive purposes including guarding against unwanted invaders. The Navy's MK 6 team trains sea lions to carry specialized ‘handcuffs’ in their mouths. The lions can attach these tracking-enabled cuffs to underwater intruders when detected. 

Dolphins and sea lions sometimes work together on such missions. For example, a dolphin may locate a swimmer and come back to the boat, and then a sea lion will go out to tag the swimmer. “He approaches an enemy swimmer with an open clamp in his mouth, and when he bumps into the swimmer, the clamp, which is attached to a line, closes around his leg, marking him on the ocean’s surface for Navy operators,” according to Coronado Times reporter Becca Garber.

The animals rely on underwater senses and superior swimming ability to defend against counterattacks.

A sea lion and US Navy diver recovery expert

3. It takes years for sea lions to ‘graduate’

The Navy has five marine mammal teams, each trained for a specific type of mission. MK 5 uses sea lions, and MK 6 uses both sea lions and dolphins. (MK is short for ‘mark’ - military jargon for a type of thing within a category.)

In San Diego, sea lions and dolphins are typically trained several times a day for several years. When the animals are ready to ‘graduate’, they take a test to become Navy certified. Some of the grads remain in San Diego while others move to Bangor, Washington, or King’s Bay, Georgia to provide coverage at the Navy bases 24 hours a day, 365 days a year. The teams can also be deployed at 72 hours' notice by ship, aircraft, helicopter, or land vehicle to regional conflicts worldwide.


GiGi, trained for underwater recovery, nuzzles merchant mariner Capt. Arne Willehag, 1983
GiGi, trained for underwater recovery, nuzzles merchant mariner Capt. Arne Willehag, 1983


4. Sea lions can remain underwater for long periods

Sea lions can remain underwater for an average of 8 to 20 minutes. Unlike dolphins, sea lions exhale before diving. While their nostrils are closed, they have special muscles to open them in order to breathe. They can dive to depths between 450 and 900 feet and have a high tolerance for carbon dioxide. The oxygen in their body concentrates in their heart and central nervous system rather than in non-vital organs.

Sea lions on the beach

5. Sea lions work with torpedoes

New York Times reporter John Ismay, who served as a Navy explosive ordnance disposal officer, was temporarily assigned to a unit at California’s Naval Amphibious Base Coronado in 1998. The base had several marine mammal detachments. One looked for trained enemy divers, another looked for naval mines floating in the water column and another searched for mines lying on the seafloor. A fourth detachment trained sea lions to help recover expensive items like inert torpedoes off the seafloor so that the Navy could reuse them.

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