air at the proper angle of attack, the aircraft's center of gravity must fall within a range specified by the aircraft's designers. An aircraft that is too nose-heavy or too tail-heavy will not fly properly, because the angle of attack is affected adversely. This can destroy lift, and cause a stall in certain maneuvers. The center of gravity of a transport aircraft is a function of a number of factors: the weight of the empty aircraft (the so-called "basic weight"), the weight of the fuel load (usually carried only in the wings), the weight of the cargo and passengers, and the weight of the crew, and the positions of each of these factors. The weight of each of these factors is known before a flight. What varies from flight to flight is not only the weight of any or all of these factors, but the position of such factors as fuel, passengers and cargo. The weight of each of these factors is converted into a "moment", by multiplying the weight of each item times its distance from a reference point which was established when the aircraft was designed. The sum of all moments is then divided by the sum of all weights and the result is the "center of gravity" for the aircraft with crew, fuel, cargo and passengers aboard. This center of gravity must be within a range specified by the designers. Furthermore, as fuel is burned off during flight the center of gravity changes continually, so that the aircraft becomes either more nose-heavy or more tail-heavy as the flight continues. This must be taken into account when the aircraft is loaded. An aircraft which was "within limits" on takeoff could, in the course of a flight, become "out of limits" because of fuel burnoff. Throughout the 1950s, loadmasters in troop carrier units were assigned primarily to aerial port squadrons. In the Military Air Transport Service, they were assigned to air transport squadrons and flew on missions when cargo was carried. MATS loadmasters were considered cabin crewmembers rather than part of the flight crew and were not afforded crew rest as were members of the cockpit crew. 1960s, the Vietnam War, and 1970s In the early 1960s with the advent of the Lockheed C-130 Hercules and the increasing role of troop carrier transports in Southeast Asia, loadmasters were reassigned from aerial port units to troop carrier squadrons where they