In the Fleet’s Operational Marine Mammal Systems (MMS), the Navy uses dolphins and sea lions to find and mark the location of underwater objects.

Dolphins are essential because their exceptional biological sonar is unmatched by hardware sonars in detecting objects in the water column and on the sea floor. Sea lions are used because they have very sensitive underwater directional hearing and exceptional vision in low light conditions.

Both of these marine mammal species are trainable for tasks and are capable of repetitive deep diving.

A Mark V "Sea Lion" System At Work
A Mark V “Sea Lion” System At Work

Some of the objects the animals find are expensive to replace. Others could present a danger to Navy personnel and vessels. The dolphins and sea lions work under the care and close supervision of their handlers and are generally trained for a particular operational capability called a “system.”

(The term “system” is engineering jargon for a collection of personnel, equipment, operations processes, logistics procedures, and documentation that come together to perform a specific job.)

However, animals may be crossed-trained for more than one system to better serve the needs of the Fleet. The term “mark” (MK for short) is military jargon for a type of thing within a category. There are 5 marine mammal systems called MK 4, MK 5, MK 6, MK 7, and MK 8. MK 4, MK 7, and MK 8 use dolphins, MK 5, which uses sea lions, and MK 6 uses both sea lions and dolphins.

These human/animal teams can be deployed within 72 hours of notice and can be rapidly transported by ship, aircraft, helicopter, and land vehicles to potential regional conflicts or staging areas all over the world. They regularly participate in major Fleet exercises.

These animals are released almost daily untethered into the open ocean, and since the program began, only a few animals have not returned.