After 55 years in flight, the US Air Force is planning to keep its biggest plane in action for a few more decades

• Since 1970, the US Air Force's C-5 cargo planes have carried troops and gear all over the world.
• The C-5 is the Air Force's biggest plane, and the latest model can haul 281,000 pounds and fly 518 mph.

In March, the US Air Force announced that it had successfully incorporated 3D-printed parts into one of its C-5M Super Galaxy strategic transport planes.

The printed parts were blocks and wedges that supported a wing hump panel, which is needed for air to flow over the wing properly. Using 3D-printing, airmen were able to produce and install the parts quickly and cheaply. The Air Force said the material used to make the parts showed "promising results" and appeared "to be impervious to natural elements."

The use of 3D parts could result in faster turnaround times and reduced costs for maintenance on the C-5, the largest aircraft in Air Force's inventory and the workhorse of US Air Force Air Mobility Command.

The announcement coincided with the anniversary of the rollout of the first C-5 from Lockheed Martin's plant in Marietta, Georgia in 1968. The plane entered service two years later, and despite a series of technical problems, it has proved its worth, playing an important role in every US conflict since then.

The Galaxy

By the 1960s, US military logistics were under increasing strain. Vehicles and equipment were getting larger and heavier, and the US's expanding set of global commitments meant they had to be transported farther.

The workload was proving to be too much for the Air Force's turboprop-powered Douglas C-133 Cargomasters and jet-powered Boeing C-135 Stratolifters and Lockheed C-141 Starlifters. The Air Force needed a single plane capable of carrying loads of over 150,000 pounds to distances over 3,000 miles.

A request for such a plane was announced in 1964. A year later, the Air Force selected Lockheed's C-5 Galaxy as the winning submission in the Cargo Experimental-Heavy Logistics System Program, or CX-HLS.

At 247 feet long, 65 feet tall, and with a wingspan of 222 feet, the C-5A was the largest plane in the world when it rolled off the production line on March 2, 1968.

It had a maximum payload of a staggering 220,000 pounds and could fly 500 mph. The pear-shaped fuselage contained a cargo hold 13 feet high, 19 feet wide, and 143 feet long. Front and rear access doors enabled easier loading, and the 28 wheels could partially deflate for landings on softer terrain.

The wheels could also partially retract to make it easier to load and unload large objects or while on uneven terrain.

The cargo hold has a reinforced deck with detachable roller lines and 36 pallet positions. The hold can also be fully pressurized, allowing the C-5 to carry up to 270 troops when seats are installed.

A second deck above the cargo hold has an 80-person passenger cabin, a crew cabin with beds, a bathroom, a kitchen, and a hay loft for extra storage. A system with hundreds of sensors throughout the aircraft monitors and reports any technical issues.

The C-5A had a range of 3,700 miles at maximum payload and was capable of aerial refueling, allowing it to extend its range whenever necessary.

Development, upgrades, and future

The C-5 was officially introduced into service in June 1970 and was almost immediately sent on missions, with its first flight to Southeast Asia a month later. Its larger carrying capacity instantly set it apart from predecessor aircraft and proved invaluable to the US military.

The C-5s were not without problems though. Cracks developed in their wings early in their service, creating a safety hazard that forced the planes to fly with well below their maximum payload. Breakdowns were also common, requiring extensive maintenance and spare parts.

The problems led crews to give the C-5 a new nickname: "FRED," short for "F---ing Ridiculous Economic/Environmental Disaster." The wing cracks became such an issue that by 1973 it was determined that all 81 C-5s that had been delivered needed new wings. Production of new C-5As was halted that year, and the first contract to re-wing the C-5s was signed in 1975.

C-5s still proved to be essential assets. They delivered nearly half of the more than 22,000 tons of military equipment given to Israel during the 1973 Yom Kippur War despite flying only about 25% of the total delivery missions. They also had a vital role in the evacuation of South Vietnam.

In October 1974, a C-5 deployed an ICBM from its cargo bay while over the Pacific, showing the US could launch ICBMs from the air.

Those successes gave the C-5 program new life. A contract for a new C-5 variant, the C-5B, was signed in 1980. The first re-winged C-5A was delivered in 1983. In 1986, the first of 50 C-5Bs was delivered, and in 1988, the first of two C-5Cs — variants used to carry equipment for the space program — were delivered.

In 1999, Lockheed began to upgrade 52 C-5s to the C-5M Super Galaxy standard, with the first flight of a converted C-5M coming in 2006. The upgrades include new avionics to increase reliability and new engines to increase thrust.

With more powerful engines, the C-5M could carry more — it has a maximum cargo capacity of 281,000 pounds — and hit a top speed of 518 mph. The Super Galaxy can fly over 5,500 miles with 120,000 pounds of cargo or nearly 8,100 miles with no cargo.

Thanks to the constant cycle of upgrades, the Air Force plans to keep its fleet of 52 C-5B/C/Ms in service until at least 2040. The service has also indicated that its C-5s and other cargo aircraft could take on new roles, including as a platform for strike missions with palletized munitions or as a mothership for unmanned aircraft.