In late 1996, the U.S. Department of Defense awarded Boeing a four-year contract to proceed with the Concept Demonstration Phase (CDP) of the Joint Strike Fighter (JSF) Program. During the 51-month-long CDP, Boeing demonstrating key technologies necessary to build, operate and maintain a truly affordable, high-performance strike fighter. Boeing also is built and flight tested two demonstrator aircraft during the CDP. The Joint Strike Fighter is the next-generation fighter to replace several aircraft in service with the U.S. Air Force, Navy, Marine Corps, the U.K. Royal Navy and several other countries' military services. Boeing planned to build all three of its service-specific variants on a single production line due to their unprecedented commonality.