2004: NASA’s X-43A unmanned scramjet aircraft becomes the first jet to break Maj William J. Knight’s X-15 record of 4,520 MPH. While the X-1, Skyrocket, X-2, and X-15 were rocket-powered, the X-43 featured an advanced scramjet engine, which allows it to cruise at 4,780 mph (Mach 6.83) for 11 seconds at 95,000 feet.