The Airborne Laser (ABL) is being built by the USAF as the primary weapon system for boost-phase defense against theater ballistic missiles. The ABL is a legacy of the Airborne Laser Laboratory built in the late 70's that demonstrated the viability of high-energy laser platforms for the future. The ABL is the first airborne laser weapon system for the 21st century, and will be the stepping stone to future high-energy laser systems.