> A regular ballistic missile hits mach 20+ on reentry but I don't know if it maintains that speed all the way to the target.
The word "ballistic" means it doesn't maintain the speed. Etymologically and practically it's about throwing a stone, i.e. finding out what happens when you give it an initial velocity with approximately zero delta-V budget for the main part of the flight.
But everything gets complicated with time, so there are now depressed trajectories (i.e. not-entirely-ballistic flight paths) for the ballistic missiles. But these still do not carry dramatic delta-V.
The word "ballistic" means it doesn't maintain the speed. Etymologically and practically it's about throwing a stone, i.e. finding out what happens when you give it an initial velocity with approximately zero delta-V budget for the main part of the flight.
But everything gets complicated with time, so there are now depressed trajectories (i.e. not-entirely-ballistic flight paths) for the ballistic missiles. But these still do not carry dramatic delta-V.