Defensive sea lions
The US Navy Marine Mammal Program would not be limited to just using dolphins, California sea lions would also be trained and deployed from the same base in San Diego, sometimes even going on missions together.
Although the sea lions lack the dolphins powerful biological sonar, they are naturally excellent divers, having very sensitive underwater directional hearing and exceptional vision in low-light conditions.
They helped to protect US harbor installations and ships against enemy divers as well as retrieving text equipment that is fired from ships or dropped from planes. The sea lions were operationally deployed with dolphins during the Vietnam War from 1965 to 1975 and in Bahrain from 1986 to 1988.
In addition to being used to identify enemy divers, sea lions were used to recover a test antisubmarine rocket from a depth of 180 feet in November 1970.