The F-82 Twin
Mustang was not, as commonly believed, two P-51s joined to a single wing.
The booms were based on the P-51 fusalage but were in fact new structures.
It was intended to provide the navigator with controls to relieve the pilot
for brief periods on very long distance missions. While it came too late for
WW II, it saw lots of action in Korea as a night fighter and was the
replacement for the P-61 Black Widow.