In the mid-1970s, DARPA and the U.S. Air Force jointly developed an airborne target-acquisition and weapon-delivery radar program, Pave Mover, under the Agency’s Assault Breaker program. The Pave Mover system relied on even earlier DARPA-sponsored research into moving target indication (MTI) radar for detecting slowly moving targets. As the program progressed, researchers added a synthetic aperture radar (SAR) to analyze areas for which the MTI radar could not detect a moving target, as well as capabilities for detecting helicopters and even rotating antennas. Also originally a part of Pave Mover was a weapon guidance feature.
These and other technologies became the basis for the Joint Surveillance and Target Attack Radar System (JSTARS) in the 1980s. And by the early 1990s, the system proved its value in Operation Desert Storm as real-time support to commanders for both battle-area situation assessment and targeting roles.
Although both the radar and the weapon guidance elements were demonstrated in the DARPA Assault Breaker program, the weapon guidance part was later dropped from the Joint STARS Program. In 1996, the Department of Defense approved JSTARS for production and deployment. The Air Force executed contracts with Northrop Grumman to modify seventeen Boeing 707-300 series aircraft into what a fleet of E-8C JSTARS, which have undergone multiple modifications and upgrades over the years.