Green Berets, elite armed force and unit of the U.S. Army specializing in counterinsurgency. The Green Berets (whose berets can be colours other than green) came into being in 1952. They were active in the Vietnam War, and they have been sent to U.S.-supported governments around the world to help combat guerrilla insurgencies. The special unit was popularized by Green Beret Barry Sadler and his song “The Ballad of the Green Berets” in 1966.