I just did the numbers.
They can travel faster than any other missile on the planet, up to 4,600mph, which is almost 66 times the speed of sound and enough to practically guarantee they cannot be targeted or intercepted.
761.2 miles per hour is the speed of sound at sea level
6.043 times the speed of sound as reported (someone can't type, I suspect)
Question: was this speed measured at sea level, or at higher altitude? I ask this due to some years ago having read an appreciation of the challenges hypersonic projectiles faced in both offensive and defensive modes.
Does anyone know the answer to where the speed measurement was made?