Military transport aircraft or military cargo aircraft are typically fixed and rotary wing cargo aircraft which are used to deliver troops, weapons and other military equipment by a variety of methods to any area of military operations around the surface of the planet, usually outside of the commercial flight routes in uncontrolled airspace. Originally derived from bombers, military transport aircraft were used for delivering airborne forces during the Second World War and towing military gliders. Some military transport aircraft are tasked to performs multi-role duties such as aerial refueling and, tactical, operational and strategic airlifts onto unprepared runways, or those constructed by engineers.