The Army, Navy, and Air Force are each developing hypersonic missiles—nonnuclear offensive weapons that fly faster than five times the speed of sound and spend most of their flight in the Earth’s atmosphere. Those missiles are intended to be maneuverable and capable of striking targets quickly from long distances. In this report, CBO analyzes the hypersonic weapons being developed by the U.S. military and compares them with less expensive existing or potential weapons that might fill similar roles, such as cruise missiles or ballistic missiles.