A new arms race is unfolding between the world's great powers. Hypersonic missiles, which are both accurate and extremely fast, stand to change the face of modern warfare by rendering the current generation of missile defense systems ineffective. As competition heats up among Russia, China and the United States to be the first to deploy hypersonic missiles, each will become more vulnerable to attack by the others. If tensions rise, so will the risk of pre-emptive strikes among the longtime rivals. Hypersonic missiles travel at least five times the speed of sound. Only a few other manmade devices are capable of reaching hypersonic speeds, including ballistic missiles, space launch vehicles and unmanned spacecraft such as the Boeing X-37. The only manned aircraft to achieve hypersonic speed is the rocket-powered North American X-15, which broke speed and altitude records when it was introduced in the 1960s.