On 14 October 1938, Curtiss test pilot Edward Elliott flew the prototype XP-40 on its first flight in Buffalo, NY. The XP-40 was the 10th production Curtiss P-36 Hawk, with its Pratt & Whitney R-1830 (Twin Wasp) 14-cylinder air-cooled radial engine replaced by a liquid-cooled, supercharged Allison v-1710 V-12 engine. The first prototype placed the glycol coolant radiator in an underbelly position on the fighter, just aft of the wing’s trailing edge. USAAC Fighter Projects Officer Lieutenant Benjamin S. Kelsey flew this prototype some 300 miles in 57 minutes, approximately 315 miles per hour. Kelsey later told reporters that future versions would likely go 100 miles per hour faster.
Kelsey was interested in the Allison engine because it was sturdy and dependable, and it had a smooth, predictable power curve. The V-12 engine offered as much power as a radial engine but had a smaller frontal area and allowed a more streamlined cowl than an aircraft with a radial engine, promising a theoretical 5% increase in top speed. Without a superchargers however, the P-40 Warhawk remained remain in service as a low altitude fighter.