In the 1950s, the U.S. Navy began studying the hydrodynamics of dolphins to design better torpedoes, ships and submarines. 20 years later, the Navy began training dolphins to detect and mark underwater mines. Today, the Navy's Marine Mammal Program includes several species of dolphins as well as sea lions that are trained to swim into enclosed spaces and mark enemy frogmen. The Navy made history in 2003 by using marine mammals for the first time in an active war zone. Shortly after the invasion of Iraq, teams of minesweeping dolphins cleared the approaches to Iraqi ports in the Persian Gulf, allowing ships with humanitarian aid to reach the Iraqi city of Basra. The dolphins detected and marked several mines, which were removed by Navy bomb-disposal teams.