Boeing E-3 Sentry

Boeing E-3A Sentry (707-300) LX-N90447
Zweibrücken, Germany

The Boeing E3 Sentry is an AWACS (Airborne Warning And Control System) aircraft developed from the Boeing 707 back in the 1970's. The last one was built in 1991, so the newest one is 30 years old. We think of the 707 as an airliner, but the first customer was the USAF (United States Air Force ) who bought the KC-135 aerial refueling tanker. So the first and last customers for the 707 were the military.
 

Boeing E3 (77-0355)
Fairbanks, Alaska

Half of the 68 units built went to the USAF, the rest went to other allied countries.

Boeing JE-3 Sentry
Fairchild Air Force Base, Spokane, Washington

Not to be confused with the E6 which is also based on the Boeing 707, nor should it be confused with the E4, which is based on the Boeing 747. Neither the E4 or the E6 carry the big radar dish on top. They are both more of a command and control kind of thing.

P.S. I added a new label, Aircraft Military Special, to cover military applications of what are essentially civilian airliners. There were getting to be too many and too hard to find.