English: An E-3 Sentry approaches a KC-10A Extender for aerial refueling June 29, 2000. The E-3 Sentry is an airborne warning and control system aircraft that provides all-weather surveillance, command, control and communications needed by commanders of U.S. and NATO air defense forces. The E-3 Sentry is modified Boeing 707/320 commercial airframe with a rotating radar dome. The dome is 30 feet in diameter, 6 feet thick and is held 11 feet above the fuselage by two struts. It contains a radar subsystem that permits surveillance from the Earth's surface up into the stratosphere, over land or water. The radar has a range of more than 200 miles for low-flying targets and farther for aerospace vehicles flying at medium to high altitudes.