Able to operate freely from nearly any place on earth, helicopters come closer than any other aircraft to achieving the birdlike freedom humanity has always envied. However, the same technology that makes this possible also prevents the helicopter from achieving the speeds and payload capacity of airplanes performing similar functions.
The Autogiro, which used unpowered rotors to provide most of its lift, was the first successful rotary-wing aircraft. The first decades of the 20th century yielded helicopters that could fly, but only marginally. In World War II, refined versions performed medical evacuation and antisubmarine warfare. During the Korean and Vietnam wars, the helicopter finally emerged as an invaluable, and then essential, military tool. Notable technological innovations have occurred since then, and today helicopters are widely used in civilian roles as well.