LOS ANGELES >> The U.S. military is planning a fourth unmanned hypersonic flight in the wake of a failed attempt.

The Air Force said Wednesday the test of an experimental X-51A Waverider will occur sometime next year. The aircraft is designed to reach six times the speed of sound after being released by a B-52 bomber.

Two months ago, a problem with a control fin during flight caused an X-51A to lose control and crash into the Pacific Ocean. It was the third X-51A test. An investigation ruled out software or power failures.

Boeing built four such vehicles for one-time use.

The purpose of the missions is to test so-called scramjet technology, which the military hopes could be used to deliver fast strikes around the world.