The Westland Whirlwind benchmark tests the counterfactual

The specified aircraft is closer to a third-generation helicopter than an experimental pioneer, moving roughly a decade and a half of development into the prewar period. The Westland Whirlwind, derived from the Sikorsky H-19 Chickasaw, provides a concrete performance target. Its roughly 95-knot speed, 7,800-pound takeoff weight, and 750-horsepower radial engine make it demanding but not wholly alien to 1939 engineering. The power requirement is only modestly above that of a Swordfish, although matching the historical engine's power-to-weight ratio would be difficult. A much smaller modern-looking machine would be the less plausible shortcut because compact engines, systems, and internal layouts required another long cycle of development. Its nearly sixteen-foot height creates the most immediate naval consequence by making existing carrier hangars uncomfortably tight.