The Boeing E-3 Sentry is an airborne warning and control system (AWACS) developed by Boeing in conjunction with Westinghouse Electric. Derived from the Boeing 707, it provides all-weather surveillance, command, control and communications, and is used by the United States Air Force (USAF), NATO, Royal Air Force (RAF), French Air Force and Royal Saudi Air Force. The E-3 is distinguished by the distinctive rotating radar dome above the fuselage. Production ended in 1992 after 68 aircraft were built.
The first USAF E-3 was delivered in March 1977, and during the next seven years, a total of 34 examples were acquired. NATO, as a single identity, also procured eighteen examples, basing them in Germany. The E-3 was also exported to the United Kingdom (seven) and France (four) and Saudi Arabia (five, plus eight E-3 derived aircraft).
In 1991, by which time the last aircraft was delivered, E-3s participated in Operation Desert Storm, playing a crucial role of directing Coalition aircraft against the enemy. Throughout the aircraft's service life, numerous upgrades were performed to enhance its capabilities.
Source: Wikipedia, "Boeing E-3 Sentry", available under the CC-BY-SA License.