The successful testing of the Douglas XC-32 led to an order for 18 similar aircraft with improvements designed to make hauling cargo more efficient. The C-33 had a two-piece, hinged cargo loading door incorporated into the aft left fuselage. The cargo floor inside the cargo door was installed at an angle so it was parallel to the ground when the aircraft was parked. This made loading and unloading cargo much easier. The aft fuselage also had three reinforced mount points for a tripod hoist assembly which could be fitted to the aircraft on the ground and used for loading and unloading cargo when a forklift or flatbed truck was unavailable. The interior of the C-33 was fitted with a cable and pulley system to aid in loading and moving cargo. There were also cargo tie-down points located throughout the interior. The vertical stabilizer was adapted from the commercial DC-3 and fitted the C-33 giving it an unofficial nickname: DC-2½.
The first C-33 (S/N 36-70) was held back at the factory and modified to become the sole C-38, which in turn was the prototype for the C-39. This modified C-33 was initially given the C-33A designation; however, the modifications were sufficient to warrant a completely new designation.
The 17 operational C-33s were used in a variety of ways at a number of bases throughout the late 1930s and into the World War II era. Besides the capability to carry a useful load of about 6,000 pounds maximum, the plane could carry 12 passengers when the interior was fitted with 12 commercial-type passenger seats. Additionally, the cabin could be converted into a hospital arrangement with space for nine litter patients and three medical attendants. The C-33s along with the C-39s received later, formed the bulk of the Air Corps airlift capability in the late 1930s up to the beginning of World War II. The C-33s continued in service until late in the war when most were removed from active service. Only one C-33 remained in service at the end of World War II and it was retired soon after.
Improved Douglas DC-2
TECHNICAL NOTES: Engines:Wright R-1820-25 radials of 750 hp each Maximum speed: 202 mph Cruising speed: 171 mph Range: 915 miles Service ceiling: 20,000 ft. Span: 85 ft. 0 in. Length: 61 ft. 6 in.
Height: 16 ft. 4 in.
Weight: 18,590 lbs. maximum gross weight Crew: Two (pilot and co-pilot) Passenger capacity: 12 passengers or 2,400 lbs. of cargo Serial numbers: 36-70 to 36-87