Hypersonic weapons have several advantages over existing cruise and ballistic missiles. Because they fly so fast, they can close on their targets in a very short period of time. Compared to slower weapons, their extremely high speed means that these weapons can evade or outrun any existing air and missile defenses. Some hypersonic weapons are so fast and maneuverable that they are unlikely to even be seen by existing radars.
Aircraft capable of hypersonic flight will be able to penetrate layered anti-aircraft defenses. During its career as one of the Air Force’s premier Intelligence, Surveillance and Reconnaissance (ISR) platforms, the venerable SR-71, which could fly at speeds up to Mach 3, was fired upon unsuccessfully hundreds of times. There are reports that a new hypersonic reconnaissance plane capable of cruising at Mach 6 is in the works.
Senior U.S. defense officials have publicly stated that Russia and China are ahead of us in this new arms race.
These things have the potential to be so destabilizing that you really don’t want to be the third guy on your block to get one.