The US Air Force has said an attempt to fly its hypersonic jet Waverider at Mach 6 (3,600mph; 5795km/h) failed.
The unmanned aircraft had been designed to fly at six times the speed of sound after being dropped from a B-52 bomber.
But officials said that a faulty control fin prevented it from starting its supersonic-combustion ramjet engine, and the craft was lost.
DARPA has repeatedly indicated an interest in developing hypersonic aircraft and weapons systems which are capable of Mach-20 speeds and thus able to reach any region of the planet within an hour. To this end, the agency has announced its new Integrated Hypersonics (IH) program, which draws upon previous research and aims to create a hypersonic X-plane (HX) ready for testing by 2016.
