"Engineers at Lockheed Martin’s Skunk Works® are working on the successor to the SR-71 Blackbird retired in 1998. With a top speed of Mach 6, or six times the speed of sound, the SR-72 will be twice as fast as its predecessor. An optionally piloted hypersonic aircraft, the SR-72 will have long range strike and reconnaissance capabilities. Lockheed Martin announced the project in 2013, and has been working on technologies for the plane for over a decade."
Interesting article on this remarkable aircraft...read here