The tests are part of the long-running HIFiRE (Hypersonic International Flight Research Experimentation) program, whose first launch took place way back in 2009. They should help bring hypersonic flight to a "range of applications," according to HIFiRE partner BAE. That could easily include ultra-fast aircraft, but it's widely believed the focus here is on missiles and similar unmanned weapons. A hypersonic missile would fulfill the US military's goal of building a conventional weapon that can strike anywhere within an hour, and it would be virtually impossible to stop using existing missile defenses. In theory, enemy nations wouldn't dare attack if they knew they'd face certain retaliation within minutes.
Originally NASA was involved in the project, which has been ongoing for more than eight years. But it's timeline may have shortened after reports that foreign powers including Russia and China are already building their own hypersonic missiles.