C-133 — The Cargomaster Survivors

Airlift has been a key strategic factor in warfare since it was developed in WWII. However, the WWII era cargo airplanes were simply airliners with the passenger seats ripped out. This left a lot to be desired. Planes like the DC-3, a taildragger, had a sloped cargo deck that was hard to load. Others sat so high off the ground that they were difficult to load and unload. Plus, the cargo had to go in and out of a side door.

The ultimate version of these early cargo planes was the Douglas C-124, often called “Old Shaky”. It did have a nose that opened up, but it was so high in the air that the drive-up ramps were nearly at a 45-degree angle. To help ease the loading of pallets, Old Shaky had a cargo elevator, which was a piece of the floor that was suspended on cables and could be lowered to the ground.

In the early 1950’s, the USAF issued a request for the first Strategic Airlifter. This was to be a plane that could carry any piece of equipment that the Air Force or Army had in inventory. The plane would need to be low to the ground to ease loading, have a drive in back door with a built-in ramp, and be able to carry a very heavy load. Finally, it would need to be pressurized to allow it to carry troops along with their equipment.

What emerged was a proposal from Douglas for the C-132, which looked a lot like a turbo-prop version of the C-5. It was huge, had swept wings, a rear door with cargo ramp, and two internal decks. In the end, the Air Force decided to hold out for an all-jet cargo plane, such as the KC-135 that was proposed and built by Boeing a few years later. The C-132 went no further than the mock-up stage.

Douglas had a backup plan in the form of an advanced development of the C-124. Designated the C-133 Cargomaster, the cargo bed was 86’10” long and about 20 feet in diameter. The wings were placed on top of the C-133 to keep the main spar from entering the cargo area. The wings were canted at a slight up angle since a plane this long would not be able to move nose-up or nose-down on take-off or landing. The main gear was placed to the side of the cargo hold to allow the cargo floor to be as close to the ground as possible. To power this beast, (4) powerful 6500HP turboprop engines were installed.

The production C-133 was 157’6” long, with a wingspan of 179’8” wide. It sat empty at 125,000 pounds, but could carry a payload of 150,000 pounds. The Cargomaster would cruise at just over 300 MPH, but could hit 359MPH at its ceiling of 19,000 feet. The C-133 entered service in the late 1950’s, and was on front line duty until they were retired in 1971. 52 were built, with 50 going to the USAF and 2 held back by Douglas as test beds. Of the 50, 15 were C-133A, 18 were C-133B, and 17 were intermediate versions.

The USAF found that the C-133 was able to carry the Thor, an early type of ICBM. Up to that point, moving ICBMs was slow, costly, and dangerous. Douglas found that with a few modifications, the C-133 could carry the modern Atlas missile. Thus was born the C-133B, which was essentially the smallest airplane that could fit around the Atlas. The B model had more powerful engines, and had a clam-shell door on the back rather than a split-ramp door. This allowed for better fitting of the Atlas missile. All C-133s in the fleet were eventually upgraded to be C-133B’s.

The C-133 served well during its service life. It was the only plane that could haul the ICBMs from the factory to bases across the US. The Cargomaster was also key in moving large and outsized cargo the US to Vietnam and back.

If there was a flaw with the C-133, it was their tendency to fall out of the sky for unexplained reasons. 10 of the 50 were lost in crashes. Many of these crashes were over water and left little or no debris. As a result, some of these crashes remain unexplained. The C-133 was also prone to stalling, especially on take off. There were also wing cracks and electrical problems. In an era of big budgets, these problems would have been solved as more planes were produced. But in the case of the C-133, its days were numbered as pure jet airlifters were being developed.

The C-133 was a majestic giant. It paved the way for modern strategic airlift, proving the concepts that would make such big successes out of the C-141, C-5, and C-17. Today, only 4 Cargomasters survive in museums, 3 are rotting away on the civilian registry, and remarkably, one has recently returned to active duty flying out of Anchorage, Alaska.

Note—Serial number research was done by Cal Taylor. His excellent web site is the C-133 Project.