These are the designations for the Navy’s marine mammals

If you know a thing or two about military life, then you've probably heard of military working dogs. These faithful animals bring a lot to the table for American troops. That being said, they aren't the only members of the animal kingdom who chip in to help. In fact, the Navy has used a number of marine mammals to assist in essential missions.

The United States Navy's marine mammal program has been around for almost six decades now. These dolphins and sea lions serve under the Navy Expeditionary Combat Command's Explosive Ordnance Disposal Group 1. Here's a rundown of these Marine Mammal Systems, listed by designation.

Dolphins that specialize in deep-water mine countermeasures are designated the Mk 4 Marine Mammal System. The dolphins pictured here are being deployed for the de-mining of New Caledonia, an allied base in World War II.

(U.S. Air Force photo by Tech. Sgt. Cohen A. Young)

Mk 4 Dolphins

These dolphins specialize in locating and neutralizing mines moored in deep water. When you think about it, it makes sense for dolphins to assist in this mission. Their echolocation is a form of sonar, which is the primary means of locating mines.

A Mk 5 is photographed during a retrieval exercise. Unlike a salvage company, it won't cost you an arm and a leg - just some fish.

(U.S. Navy)

Mk 5 Sea Lions

These sea lions are used for the retrieval of submerged objects. Unlike human divers, sea lions can dive deep without suiting up for the mission. What's more is that these highly-trained mammals will happily hand over whatever they find in exchange for a fishy treat.

This Mk 6 Marine Mammal System looks friendly and playful... unless you're an enemy swimmer. Then he'll take you down without remorse, thinking only of the extra fish he'll get as a reward.

(U.S. Navy photo by Journalist 1st Class Wes Eplen)

Mk 6 Dolphins and Sea Lions

We all do our best to keep intruders out of our yards. Well, the Navy does the same for their harbors. And for good reason: Enemy swimmers can do damage — just ask the crew of USNS Card (T-AKV 40). The dolphins and sea lions in this system are intended to find and help detain enemy divers. The water is their natural element; intruders stand little chance of escaping.

Mk 7 Marine Mammal Systems handle the shallow-water mine countermeasures mission.

(U.S. Navy photo by Mr. John F. Williams)

Mk 7 Dolphins

There are some places laden with mines that drones or ships simply can't reach. In order to best protect troops and technology, these dolphins use their sonar and agility to clear the way. After all, their natural ability is arguably superior to current mine-detecting technologies.

These dolphins find safe lanes for landing craft and amphibious assault vehicles to use for delivering Marines ashore.

(U.S. Navy photo by Chief Mass Communication Specialist Elena Pence)

Mk 8 Dolphins

When storming a beach, you first need to find a safe lane for your landing craft and amphibious assault vehicles to travel within. These dolphins are specially trained to use their echo-location techniques to find a safe canal.

Now, before you get up in arms, know that these dolphins and sea lions tend to live longer than their wild counterparts. They also get excellent care from veterinarians and experienced trainers throughout. While the Navy is working on underwater drones, the fact is, these Marine Mammal Systems have served well for almost six decades and will likely continue to serve alongside sailors and Marines for a long time yet.