Aircraft capable of hypersonic flight will be able to penetrate layered anti-aircraft defenses. During its career as one of the Air Force’s premier Intelligence, Surveillance and Reconnaissance (ISR) platforms, the venerable SR-71, which could fly at speeds up to Mach 3, was fired upon unsuccessfully hundreds of times. A new technological competition has begun, one in which America’s rivals, particularly Russia and China, may be ahead. This is the race to build and put in the field super-fast or hypersonic weapons and vehicles. The military defines a hypersonic weapon as one that travels at least Mach 5 or five times the speed of sound. In comparison, commercial aircraft fly at around Mach 1 while some military jets can push themselves to around Mach 3, but only for a short time.There are two basic types of hypersonic weapons: super-fast cruise missiles, and boost-glide vehicles that are mounted on ballistic missiles. Hypersonic cruise missiles, which would most commonly be launched from aircraft, maintain powered flight from launch to impact. Boost-glide vehicles are lofted by a ballistic missile launched from an aircraft, ship, submarine or ground unit to the edge of space from which point they use their speed and aerodynamic design to skip along the top of the atmosphere for up to 10,000 miles.(This first appeared in June 2019.)