The Lockheed C-40 was based on the commercial Model 12 Electra Junior. The Model 12 was essentially a scaled down version of the Lockheed Model 10 Electra. The Air Corps already had several Electras in service and designated them C-35, C-36 and C-37.
The Model 12 was designed initially as a small commercial airliner capable of carrying five or six passengers. It used the same engines as the Model 12 and was about 20 mph faster due to its smaller size.
The Air Corps tested a Lockheed company demonstrator Model 12 at Wright Field, Ohio, during the summer of 1938. In the fall of the same year, the Army bought the plane along with two more Model 12-A Electra Juniors and designated them C-40.
The C-40s were used primarily as staff transport planes from 1939 through the early years of World War II. The Army declared the C-40s surplus in the middle of WWII and sold most of them -- some to foreign air forces.
Model 12 Electra Junior
Tricycle landing gear testbed
Designation not used
Impressed Electra Juniors
TECHNICAL NOTES: Engines: Two Pratt & Whitney R-985-17 radials of 450 hp each Maximum speed: 218 mph Cruising speed: 208 mph Range: 800 miles Service ceiling: 22,900 ft. Span: 49 ft. 6 in. Length: 36 ft. 4 in. Height: 9 ft. 9 in. Weight: 9,200 lbs. maximum gross weight Crew: Two (pilot and co-pilot) Passenger capacity: 5 Serial numbers: C-40: 38-536 to 38-538; C-40A: 38-539 to 38-548; C-40B: 38-582; UC-40D: 42-22249, 42-38280, 42-38346 to 42-38352, 42-57504, 42-66386