A bottlenose dolphin named K-Dog leaps out of the water in front of Sgt. Andrew Garrett while training near the USS Gunston Hall in the Persian Gulf on March 18, 2003. Reuters/US Navy/Brien Aho Until the introduction of modern machinery, animals played an often decisive role in warfare.

For instance, the Mongols' masterful use of horses allowed Genghis Khan and his generals to carve out the largest land empire ever.

In the book "Beasts of War: The Militarization of Animals," author Jared Eglan curated amazing insights into how militaries have used a stunning menagerie of animals in combat.

One of the more surprising animals that humans have managed to militarize are dolphins.

In 1960, the US Navy first began its studies on dolphins. At first, they were limited to testing how dolphins were so hydrodynamic, with efforts on applying the findings toward improving torpedo performance.

But by 1967, the US Navy Marine Mammal Program evolved into a major project. The program, still going, began training dolphins for mine-hunting and force-protection missions.

In the case of mine hunting, dolphins were trained to locate underwater mines and release buoys over their location, allowing the Navy to safely clear the weapons.

Petty Officer 2nd Class Joshua Scott/US Navy

During the Iraq War in 2003, such dolphin-led operations led to the clearance of over 100 mines in the port of Umm Qasr. Additionally, dolphins have been trained to guard harbors against enemy divers. When a diver approached, the dolphin was trained to bump a buoy device onto the person's back, which would drag them to the surface.

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

The US is not alone in its militarization of dolphins. Russia also has its own militarized-dolphin divisions, which it seized from Ukraine during the annexation of Crimea in 2014. The dolphin division was first created by the Soviet Union.

And in the beginning of March, Russia announced that it was looking to buy five more dolphins for the unit — two females and three males.

After Russia's seizure of the dolphins in March 2014, RIA Novosti wrote that the "dolphins are trained to patrol open water and attack or attach buoys to items of military interest, such as mines on the sea floor or combat scuba divers trained to slip past enemy security perimeters, known as frogmen."