The United States and China are engaged in an arms race to develop the most lethal hypersonic weapons, the U.S. Air Force secretary said on Tuesday, as Beijing and Washington build and test more and more of the high-speed next-generation arms. 'There is an arms race, not necessarily for increased numbers, but for increased quality,' Air Force Secretary Frank Kendall told Reuters during an interview in his Pentagon offices. 'It's an arms race that has been going on for quite some time. The Chinese have been at it very aggressively.' In October, the top U.S. military officer, General Mark Milley,...