“Aerojet Rocketdyne successfully completed two hot-fire tests of a rocket motor designed to boost an air-launched tactical glide hypersonic vehicle during its initial phase of flight…The difficulty in defending against hypersonic weapons has pushed the Pentagon into an arms race. Developing hypersonic weapons is the ‘highest technical priority’ for the US military, said Michael Griffin, undersecretary of defense for research and engineering, in March 2018.”
Source: Aerojet Rocketdyne successfully tests rocket booster for hypersonic vehicle