The U.S. NAVY MARINE MAMMAL PROGRAM: Since 1959, the U.S. Navy has trained dolphins and sea lions  to help guard against threats underwater….Dolphins naturally possess the most sophisticated sonar known to science. Mines and other potentially dangerous objects on the ocean floor that are difficult to detect with electronic sonar, especially in coastal shallows or cluttered harbors, are easily found by the dolphins. Both dolphins and sea lions have excellent low light vision and underwater directional hearing that allow them to detect and track undersea targets, even in dark or murky waters. They can also dive hundreds of feet below the surface, without risk of decompression sickness or “the bends” like human divers. Someday it may be possible to complete these missions with underwater drones, but for now technology is no match for the animals…Dolphins are trained to search for and mark the location of undersea mines that could threaten the safety of those on board military or civilian ships..
How do the animals travel to remote work sites? By airplanes and helicopters (yes!)

Excerpt from US Naval Information Warfare Center