A cruise missile is a guided missile which carries an explosive payload and uses a lifting wing and a propulsion system, usually a jet engine, to allow sustained flight; it is essentially a flying bomb. Cruise missiles are generally designed to carry a large conventional or nuclear warhead many hundreds of miles with high accuracy. Modern cruise missiles can travel at supersonic or high subsonic speeds, are self-navigating, and fly on a non-ballistic very low altitude trajectory in order to avoid radar detection. In general (and for the purposes of this article), cruise missiles are distinct from unmanned aerial vehicles (UAV) in that they are used only as weapons and not for reconnaissance, the warhead is integrated into the vehicle, and the vehicle is always sacrificed in the mission.