During the Vietnam War, these intense operations of the late 1960s and early 1970s persuaded the US. Air Force of its urgent need for advanced electronic escort type with the performance to support strike package of first line aircraft. In 1975 the USAF contracted with Grumman for two examples of General Dynamics F-111A interdictor converted into EF-111A electronic escort. The second of these was the definitive prototype, and first flew in March 1977. The heart of the EF-111A is the EA-6B Prowler's ALQ-99 tactical radar detection and jamming system repackaged and automated as the ALQ-99E for operation by a single operator. The First EF-111 enter survive in November 1981, and the last of 42 conversions was delivered in 1985. since that time the avionics and electronic have been updated extensively.