From "Yesterday, Today, Tomorrow – Fifty Years Fairchild Aviation":

The Fairchild XC-31 was the first airplane specifically designed as a military cargo carrier. Powered by a 750-hp Wright Cyclone engine, the XC-31 carried nearly three tons of payload, more than any single-engine airplane. Top speed was 167 mph (269 kmh) with a range of 750 mls (1207 km). First flown in 1934, the strut-braced, high-wing monoplane also could be fitted out as a hospital plane or a troop carrier for fourteen soldiers. Outsize 5 ft (1.52m) doors provided easy access to the 100 sq.ft (9.3 sq.m) of unobstructed floor space in the cargo compartment. The cargo deck was 4 ft (1.22 m) above ground, exactly matching the height of the Army truck beds for easy loading.