Two bomb bays were fitted mid-fuselage, capable of carrying of bombs, although in practice such a bomb load reduced range too much, and the aft bomb bay was usually fitted with additional fuel tanks instead of bombs. The aircraft was powered by two Pratt & Whitney R-2800 Double Wasp radial engines in nacelles slung under the wing, driving four-bladed propellers. The engines were manufactured at the Ford Dearborn Engine plant in Dearborn, Michigan, USA. The wings were of low aspect ratio and relatively small in area for an aircraft of its weight, giving the required high performance, but also resulting in a wing loading of for the initial versions, which at the time was the highest of any aircraft accepted for service by the Army Air Corps, until the introduction of the Boeing B-29 Superfortress, with the then-astonishing wing loading of (although both would be considered lightly loaded by the standard of combat aircraft of the next decade).