Washington, May 16 : The US Department of Defense "is working on developing a range of hypersonic missiles", press secretary Jonathan Hoffman said. Hoffman's remarks on a tweet on Friday came hours after President Donald Trump said the US was "building right now incredible military equipment", reports Xinhua news agency "We have, I call it the Super Duper Missile, and I heard the other night 17 times faster than what they have right now," he said at an Oval Office event, where he unveiled the official flag of the US Space Force. Hypersonic weapons can travel at five times the speed of sound and faster, according to Raytheon Technologies, a major US defence contractor. The Center for Public Integrity, a US investigative journalism organization, tweeted on Friday that hypersonic missiles "are touching off a new global arms race that threatens to change the nature of warfare". The US has spent far more than any other country in the world to build armed forces and make weapons. /IANS