By May 2000, the first four Boeing-built 767 Airborne Warning and Control System (AWACS) aircraft had entered operational service for the Japan Air Self Defense Force (JASDF). The aircraft were delivered by Boeing between 1998 and 1999. In meeting JASDF requirements, the aircraft underwent rigorous testing of their navigation, communication and radar systems. Operational tests with Japan's fighter jet fleet also were conducted. The aircraft are based in Hamamatsu, Japan. AWACS, the world's standard for airborne early warning & control systems, fills the need for both airborne surveillance and command and control functions for tactical and air defense forces.