The McDonnell XHJH Whirlaway, aka McDonnell Model 37, is a 1940s American experimental transverse-rotor helicopter designed and built by McDonnell Aircraft Corporation for the United States Navy and was the largest helicopter at the time, as well as the first successful twin-engined twin-rotor helicopter in the world.

[1][2][3][4] In 1944, the United States Navy issued a requirement for a large rescue helicopter with capacity for ten occupants.

James McDonnell had invested in that company in 1942 and some of his engineers had been working there, gaining experience of helicopter design and production techniques.

It had twin side-by-side 46 ft (14 m) rotors at the end of pylon wings which turned in opposite directions.

Each rotor was powered by a 450 hp (336 kW) Pratt & Whitney R-985-AN-14B Wasp Junior engine.