Development of hypersonic weapons and defenses in the United States was limited to basic research a decade ago. Then, during the Trump administration, the Pentagon’s Michael Griffin warned in a 2018 Senate hearing about China’s hypersonics prowess. Russia had rattled its hypersonic saber a month before — and a year later, China did too. U.S. hypersonics research boomed into a multibillion-dollar annual enterprise, a level the Biden administration has maintained and even slightly increased. It was Mark Lewis, a former Air Force chief scientist with a Ph.D. from MIT, who guided much of the research from 2019 to 2021 as the Pentagon’s director of research and engineering for modernization. Lewis is now head of the Purdue Applied Research Institute, the Purdue University-affiliated organization that aims to be an incubator for transitioning research into real-world innovations in national security and other fields. I spoke to Lewis over the phone to learn just how worried the U.S. should be and what can be done to defend against these weapons.