SAN DIEGO

For a moment, the mammal and the machine are side by side on a Navy dock here. The dolphin and the drone — and their handlers — will spend the morning training for a possible order to deploy to the Persian Gulf or some other international trouble spot to detect underwater mines, or maybe to guard a port against a terrorist threat.

The mammal is Puanani, a bottlenose dolphin, a sleek 7 feet, 10 inches long and 427 pounds. The machine is an Unmanned Underwater Vehicle, or UUV, Kingfish version, 11 feet long, 600 pounds.

Puanani received initial training from the Navy in Hawaii. The cigar-shaped UUV was built by Hydroid Inc., a Massachusetts military contractor.

Both are assigned to a mission that Navy officials say is increasingly critical: maintaining "underwater dominance" and the ability to thwart attacks aimed at the home front or at U.S. and allied ships in foreign locations.

The U.S. has submarines, advanced sonar aboard surface ships and high-tech scanning capability aboard aircraft — as well as listening devices beneath the waves and an untold number of technological and intelligence-gathering assets that are classified.

A bottlenose dolphin reacted to its trainer while a sea lion practiced on a simulated mine, above, at the Mine and Anti-Submarine Warfare Center in San Diego, Calif.

In San Diego, with a budget of $28 million a year, the Navy has 90 dolphins and 50 California sea lions in a program run by the Space and Naval Warfare System Pacific. Nearly every day the animals train in San Diego Bay or in the ocean beyond Point Loma. The dolphins and the sea lions, using their keen eyesight and "biological sonar," are expert at finding mines. The sea lions are trained to detect any swimmer who is in a restricted area. The animal clamps a "bite plate" onto the swimmer's leg and takes the attached tether back to his handler.

Puanani was sent to the Persian Gulf during the invasion of Iraq. "She is deployable any time, anywhere," said Mark Patefield, Puanani's lead trainer. "All we need is the word 'go.'"

Someday the UUVs may replace the mammals in the mine-detection mission. Until then the two share the assignment. "The mammals are the best at what they do," said Mike Rothe, manager of the marine mammals program. "They've evolved over thousands of years to have a remarkable sonar. We've been developing the UUVs for several decades."