With Pratt & Whitney starting development of their own 46 liter-displacement eighteen-cylinder, twin-row high-output radial as the Double Wasp in 1937, Wright's first R-3350 prototype engines — itself having a nearly 55 liter displacement figure — were initially run in May of the same year. Continued development was slow, both due to the complex nature of the engine, as well as the R-2600 receiving considerably more attention. The R-3350 did not fly until 1941, after the prototype Douglas XB-19 had been redesigned from the Allison V-3420 to accept the R-3350.