The massive Lockheed C-5 is one of the largest military aircraft in existence. With its unrivaled cargo capacity, the aircraft remains a work horse of the U.S. Air Force. 131 C-5s were produced in the C-5A and C-5B models. The entire fleet is currently undergoing a major upgrade to become the C-5M Super Galaxy, with new engines, and modern avionics. This upgrade will extend the life of the aircraft to the year 2040.