The United States Air Corps wanted the aircraft to perform high altitude research and to test the feasibility of a pressurized cabin.
The XC-35 was fitted with two Pratt & Whitney XR-1340-43 engines of 550 hp (410 kW) each compared to the two Pratt & Whitney R-985-13 of 450 hp (336 kW) fitted to the base Model 10 Electra.