The HCU-6/E or 463L Master Pallet is a standardized pallet used for transporting military air cargo. It is the main air-cargo pallet of the United States Air Force, designed to be loaded and offloaded on today's military airlifters as well as many civilian Civil Reserve Air Fleet (CRAF) cargo aircraft.
The "SS-463L" project was developed by a U.S. Air Force committee in 1957 and awarded to the Douglas Aircraft Company in 1959. The "SS-463L Pallet Cargo Handling System" specifications for aircraft (aka "463L") included a "Master Pallet" design to meet a component of the material handling specifications of this system. The "Master Pallet" was contracted to the AAR Cadillac Manufacturing Corporation, at one time AAR Cadillac Corp, and now AAR Corporation.
In the 1950s, the U.S. Air Force used a standard designation system for all awarded projects. The "SS" represents (Support System), the "463" represents an assigned general system category, 400–499 series for "Support Systems", and the suffix "L" also represents "Support Systems". Thus, "463L" is the name of the system.