Delta Ship 6301 when it was a Boeing 747-400 prototype. Boeing Pratt & Whitney then used the aircraft as a test bed for its PW4000 series engines, which would power all of Delta's 747-400s.

Delta Ship 6301 when it was a Boeing 747-400 prototype. Boeing Pratt & Whitney then used the aircraft as a test bed for its PW4000 series engines, which would power all of Delta's 747-400s.

The Boeing 747-400 known as Delta Ship 6301. Benjamin Zhang/Business Insider The aircraft, Delta Ship 6301, was the first Boeing 747-400 ever built and entered service with Northwest Airlines in 1989.