The US ICBMs are sent up to 1 200 000 m altitude by a rocket from where they then drop down almost vertically to arrive at the top of the atmosphere at 130 000 m altitude at say 6 500 m/s and increasing velocity a little later.
No, that isn't quite how ICBMs work.
Well, the following flight phases of an ICBM can be distinguished (
https://en.wikipedia.org/wiki/Intercontinental_ballistic_missile ):
boost phase: 3 to 5 minutes; it is shorter for a solid-fuel rocket than for a liquid-propellant rocket; depending on the trajectory chosen, typical burnout speed is 4 km/s (2.5 mi/s), up to 7.8 km/s (4.8 mi/s);
altitude at the end of this phase is typically 150 to 400 km (93 to 249 mi).
midcourse phase: approx. 25 minutessub-orbital spaceflight with a flightpath being a part of an ellipse with a vertical major axis;
the apogee (halfway through the midcourse phase) is at an altitude of approximately 1,200 km (750 mi); the semi-major axis is between 3,186 and 6,372 km (1,980 and 3,959 mi); the projection of the flight path on the Earth's surface is close to a great circle, slightly displaced due to earth rotation during the time of flight; the missile may release several independent warheads and penetration aids, such as metallic-coated balloons, aluminum chaff, and full-scale warhead decoys.
re-entry phase (starting at an altitude of 100 km, 62 mi): 2 minutes
impact is at a speed of up to 7 km/s (4.3 mi/s) (for early ICBMs less than 1 km/s (0.62 mi/s)); see also maneuverable reentry vehicle.
ICBMs usually use the trajectory which optimizes range for a given amount of payload (the minimum-energy trajectory); an alternative is a depressed trajectory, which allows less payload, shorter flight time, and has a much lower apogee.
Of course the real details are military secrets. IMO the whole thing doesn't work at all.
http://heiwaco.com/bomb.htm .