The Lockheed Martin Skunk Works® facility in Palmdale, California, performed maintenance on one of just two C-5C Galaxy aircraft in the world in May 2013.  
The C-5C features more cargo capacity than A & and B models due to removal of the entire passenger compartment.

Each of the two C-5C aircraft is assigned to Travis Air Force Base, Calif., and will eventually be modernized to become the C-5M Super Galaxy.
The C-5M Super Galaxy incorporates more than 70 aircraft improvements to the largest aircraft in the U.S. Air Force inventory. While setting 43 world records in airlift, this strategic airlifter is in a class of its own.

The Lockheed C-5 Galaxy is a large military transport aircraft built by Lockheed. It provides the United States Air Force (USAF) with a heavy intercontinental-range strategic airlift capability, one that can carry outsize and oversize cargos, including all air-certifiable cargo.

The Galaxy has many similarities to its smaller C-141 Starlifter predecessor, and the later C-17 Globemaster. The C-5 is among the largest military aircraft in the world.
The C-5 Galaxy had a complicated development; significant cost overruns were experienced and Lockheed suffered significant financial difficulties. Shortly after entering service, fractures in the wings of many aircraft were discovered and the C-5 fleet were restricted in capability until corrective work was conducted. The C-5M Super Galaxy is an upgraded version with new engines and modernized avionics designed to extend its service life beyond 2040.

The C-5 Galaxy has been operated by USAF since 1969. In that time, it has been used to support US military operations in all major conflicts including Vietnam, Iraq, Yugoslavia and Afghanistan; as well as in support of US allies, such as Israel during the Yom Kippur War and NATO operations in the Gulf War.
The C-5 has also been used to distribute humanitarian aid and disaster relief, and support the US Space Shuttle program run by NASA.