During the 1940s, James McDonnell became interested in helicopters and formed a helicopter division within the McDonnell Aircraft Corp.

McDonnell Aircraft developed the world’s first twin-engine twin-rotor helicopter, the XHJD-1 Whirlaway, an experimental utility helicopter for the Navy antisubmarine and Coast Guard search-and-rescue operations, and capable of being put into production.

A notable feature of the Whirlaway was the use of two engines, one for each rotor. A complex transmission system was developed to enable one engine to power both rotors, as a precaution to engine failure.

Larger than any helicopter then in existence, and the first with two engines, the XHJD-1 was intended to be a testbed for study of the rotor aerodynamics.