The USAF C-5A/B Galaxy and C-5M SuperGalaxy

The Unites States Air Force (USAF) are the only operator of the C-5 Lockheed Galaxy.

The Lockheed C-5 Galaxy is a large military transport aircraft originally designed and built by Lockheed, and now maintained and upgraded by its successor, Lockheed Martin. It provides the United States Air Force (USAF) with a heavy intercontinental-range strategic airlift capability, one that can carry outsized and oversized loads, including all air-certifiable cargo. The Galaxy has many similarities to the smaller Lockheed C-141 Starlifter and the later Boeing C-17 Globemaster III. The C-5 is among the largest military aircraft in the world.

The C-5 Galaxy's development was complicated, including significant cost overruns, and Lockheed suffered significant financial difficulties. Shortly after entering service, cracks in the wings of many aircraft were discovered and the C-5 fleet was restricted in capability until corrective work was completed. The C-5M Super Galaxy is an upgraded version with new engines and modernized avionics designed to extend its service life beyond 2040.

The USAF has operated the C-5 since 1969. In that time, the airlifter supported US military operations in all major conflicts including Vietnam, Iraq, Yugoslavia, and Afghanistan, as well as allied support, such as Israel during the Yom Kippur War and operations in the Gulf War. The Galaxy has also been used to distribute humanitarian aid and disaster relief, and supported the US space program.

C-5A

Instrument panel of a C-5A
The C-5A is the original version of the C-5. From 1969 to 1973, 81 C-5As were delivered to the Military Airlift Command of the U.S. Air Force. Due to cracks found in the wings in the mid-1970s, the cargo weight was restricted. To restore the C-5's full capability, the wing structure was redesigned. A program to install new strengthened wings on 77 C-5As was conducted from 1981 to 1987. The redesigned wing made use of a new aluminum alloy that did not exist during the original production.[94] As of August 2016, there were 10 A-models in service flown by the Air Force Reserve Command's 433d Airlift Wing at Lackland AFB / Kelly Field, Texas, and 439th Airlift Wing at Westover ARB, Massachusetts.[95] The last operational C-5A was retired on 7 September 2017.[96]

C-5B
The C-5B is an improved version of the C-5A. It incorporated all modifications and improvements made to the C-5A with improved wings, simplified landing gear, upgraded TF-39-GE-1C turbofan engines and updated avionics. 50 examples of the new variant were delivered to the U.S. Air Force from 1986 to 1989.[97][98]

C-5C
The C-5C is a specially modified variant for transporting large cargo. Two C-5s (68-0213 and 68-0216) were modified to have a larger internal cargo capacity to accommodate large payloads, such as satellites. The major modifications were the removal of the rear passenger compartment floor, splitting the rear cargo door in the middle, and installing a new movable aft bulkhead further to the rear.[99] The official C-5 technical manual refers to the version as C-5A(SCM) Space Cargo Modified. Modifications also included adding a second inlet for ground power, which can feed any power-dependent equipment that may form part of the cargo. The two C-5Cs are operated by U.S. Air Force crews for DOD spacecraft programs and NASA, and are stationed at Travis AFB, California. Both C-5Cs #68-0213 and #68-0216 have been modified into C-5Ms as of 2017.[citation needed]

C-5 AMP and C-5M Super Galaxy

New C-5 cockpit avionics, installed under the Avionics Modernization Program
Following a study showing 80% of the C-5 airframe service life remaining,[100] Air Mobility Command (AMC) began an aggressive program to modernize all remaining C-5Bs and C-5Cs and many of the C-5As. The C-5 Avionics Modernization Program (AMP) began in 1998 and includes upgrading avionics to Global Air Traffic Management compliance, improving communications, new flat panel displays, improving navigation and safety equipment, and installing a new autopilot system. The first flight of a C-5 with AMP (85-0004) occurred on 21 December 2002.[101]

The Reliability Enhancement and Re-engining Program (RERP) began in 2006. It includes new General Electric F138-GE-100 (CF6-80C2) engines, pylons and auxiliary power units, upgrades to aircraft skin and frame, landing gear, cockpit and pressurization systems.[45][102] Each CF6 engine produces 22% more thrust (50,000 lbf or 220 kN),[103] providing a 30% shorter takeoff, a 38% higher climb rate to initial altitude, an increased cargo load and a longer range.[specify][45][104] Upgraded C-5s are designated C-5M Super Galaxy.[105]