Air assault is the movement of ground-based military forces by vertical take-off and landing (VTOL) aircraft, such as helicopters, to seize and hold key terrain that has not been fully secured, and to directly engage enemy forces behind enemy lines. In addition to regular infantry training, air-assault units usually receive training in rappelling, fast-roping techniques, and air transportation. Their equipment is sometimes designed or field-modified to allow better transportation and/or carrying within aircraft.

A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of short take-off and landing (STOL) or short take-off and vertical landing (STOVL) aircraft cannot perform without a runway.