Dolphins have been trained to be used in wars by the U.S. and Soviet Union.
The Navy's Marine Mammal Program began in 1960 with two goals. First, the Navy wanted to study the underwater sonar capabilities of dolphins and beluga whales to learn how to design more efficient methods of detecting objects underwater and to improve the speed of their boats and submarines by researching how dolphins are able to swim so fast and dive so deep.
In addition to this research component, the Navy also trained dolphins, beluga whales, sea lions and other marine mammals to perform various underwater tasks, including delivering equipment to divers underwater, locating and retrieving lost objects, guarding boats and submarines, and doing underwater surveillance using a camera held in their mouths. Dolphins were used for some of these tasks in the Vietnam War and in the Persian Gulf. The Marine Mammal Program was originally classified and was at its peak during the Cold War.
The Soviet Union's military was conducting similar research and training programs in the race to dominate the underwater front. At one point during the 1980s, the U.S. program had over 100 dolphins, as well as numerous sea lions and beluga whales, and an operating budget of $8 million dollars.
By the 1990s, however, the Cold War was over, and the Navy's Marine Mammal project was downsized. In 1992, the program became declassified. Many of the dolphins were retired, and controversy arose over whether or not it would be feasible to return unnecessary dolphins to the wild.