Have a read of how MERV part of some ICBMs works. Lots going on as far as targeting goes. Also take a look at Trident 2 which can use GPS for course correction but isn’t reliant on it.

That's exactly the right interpretation. You chuck them into space and after the rocket quits, Isaac Newton takes over.

Contrast hypervelocity weapons, which -- contrary to the name -- don't really go faster but they can maneuver in the atmosphere at that speed.