The Harrier is the first operational V/STOL (Vertical/Short Takeoff and Landing) aircraft. By directing the engines exhaust through movable nozzles the force could be used to propel the aircraft along a runway or lift it vertically and then into a forward motion. Because of this ability to lift off vertically the Harriers began to be referred to as jump jets. These aircraft were continuously being refined and improved over the years with many new variants being produced.