Boeing 707-300 (71-1408)

The second Boeing EC-137D 71-1408 at Boeing Field in Seattle on June 18, 1973. Its construction number is 20519. It differed from the production E-3 Sentry in having the full complement of passenger windows and bare metal fuselage. It was held by Boeing for tests before it was converted to E-3A standard. It was delivered to the Air Force as an E-3A on December 15, 1978. It was later converted to E-3B standard.