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 seafloor. 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.

The Mark 6 System

  • MK 6 MMS was first operationally deployed with dolphins during the Vietnam War from 1971 to 1972, and Bahrain from 1986 to 1987.
  • MK 6 has now been expanded to include specially trained sea lions to locate water-borne intruders and suspicious objects near piers and ships that pose a possible threat to military forces in the area. They have been shown to be effective under and around ships, piers, and in open water.
  • The sea lions were deployed to Bahrain as part of the effort to support missions under Operation Enduring Freedom.

Read more on the Navy’s site.

My Experience Diving Against Dolphins

If you’ve read my memoir, The Red Circle, you know about my time diving closed-circuit (no bubbles) Drager against the US Navy’s Dolphins. The Marine Mammal Unit would often work them into our training dives, although we admittedly knew very little about their capabilities. We just knew that you didn’t want to get hit by them – it was not a pleasant experience for those SEALs that got nailed in the murky night water.

Navy SEAL With The LAR V Drager
Navy SEAL With The LAR V Drager

There were always rumors in the UDT/SEAL Teams about the CO2 anti-swimmer cartridges used by the dolphins. The concept is a simple one: dolphin hits an enemy diver with a CO2 dart that injects him with compressed nitrogen, diver has an embolism, and diver is dead. It’s a very efficient and extremely hard to defend against.

I recently phoned two of my former colleagues who are still on active duty and asked them if they could confirm the rumor, and neither could. So I asked myself the question, did the US Navy EVER consider CO2 darts with regards to harbor anti-swimmer defense? I was shocked to find open source evidence that appears to admit that yes, they did.

A while back Wired Magazine’s Danger Room interviewed the Marine Mammal Program’s Public Affairs Officer Tom LaPuzza on this topic.

Wired Magazine’s Interview Dialogue:

Excerpt Question: But given their capabilities, was there never a temptation to turn marine mammals into lethal weapons?

Sea World: Retirement home for the Navy’s dolphins

Read Next: Sea World: Retirement home for the Navy’s dolphins

“Absolutely not”, insists LaPuzza, although there have been rumors for decades about a sinister “Swimmer Nullification Program” since Vietnam days.

SOFREP Confirms The CO2 Death Injection


I was digging through historical documents on the US Navy Marine Mammal Systems (MMS) program and came across an old PowerPoint slide pictured below that specifically mentioned the CO2 Dart System.

I also received confirmation that the weaponized dolphin program does in fact exist, at least in the late nineties when our anonymous Navy SEAL source was diving against them in several combat diver tests. He was actually involved in over a dozen dolphin vs. combatant swimmer operations.


Anonymous Navy SEAL:

“One of the MK 6 dolphins was named Jake and he was a real bastard to dive against. All the dolphins were very intelligent but none matched Jake’s aggression. They eventually retired him and I heard that this dolphin actually had enemy diver KIA.

We would do several dives a day and try everything to avoid detection, hiding under boats next to the keel, stirring up silt from the bottom, and hiding among pier pilings. Nothing worked to our advantage, the longest time it took one of the dolphins to find and simulate a kill on seven pairs of divers was within minutes.

The dolphins would have their simulated CO2 system attached to their nose, they would then ram us in the chest cavity to simulate the injection. The dolphins could kill just with this force alone (we had to dive with special padding) but the idea was to recover the bodies and any intelligence.

I actually saw one of the heavy gauge needles that attaches to their nose along with the harness and CO2 containers that were positioned just behind the head. They’re incredibly smart mammals and not pleasant to dive against.” -Anonymous Navy SEAL

I guess the rumors are confirmed. So be careful Mr. Terrorist, you may want to avoid diving around high profile U.S. harbors, that is, unless you want bulging eyes and an exploding chest cavity.

Side note: You’ll have to read The Red Circle if you want to know how to defeat a MK 6 Dolphin.