The Japanese AWACS (E-767) March 23 2016
Back in the 70s there was a Russian pilot who defected to Japan flying a Mig-25 (score for the Americans!). The Mig-25 was out of radar when the pilot flew at low level. This made the Japanese realize that they needed an Airborne Warning and Control System (AWACS).
At that time, the E-3 Sentry was the standard, but due to the delivery commitments to the USAF, that E-3 would not be readily available. This prompted the selection instead of the E-2 Hawkeye system (which the US NAVY uses).
It was not until 1991 when the Japanese wanted to upgrade their AWACS but by that time, the 707 which the E-3 was based, was out of production. However, the following year, some very smart people at Boeing (all engineers, of course) offered to package the E-3 systems into the 767-200 airframe.
And what an improvement it was, other than being more efficient, due to better engines and the fact that you go from four engines to two, the 767 offered 50% more floor space and nearly double the volume of the 707 airframe.