I was wrong again........but intuition is telling me it would be better to launch the things across the ocean...........I am not sure exactly why.............maybe b/c it is cold in the poles........and that would affect the missiles............and maybe windy.............the South pole...........the Antarctic is the windiest place on Earth.............but they would probably go across the artic, the North pole or the Pacific ocean..........so who knows, maybe I am wrong........but they are up to something that I am sure......



Yes, the Earth curvature does change with the latitude, but not for the reasons you wrote. Other posters above explained why you were wrong in that sense. However, the Earth is not a perfect sphere, it is slightly flattened at the poles. It means the curvature is indeed different at poles than on the equator. The difference is rather negligible though - according to NASA, the polar radius is 6,356,752 m and the equatorial radius is 6,378,137 m (Wiki claims a bit different values).

EDIT: The calculation would be a more complicated than I originally posted, so I removed it. Also, except of the poles, the horizon distance is not perfectly isotropic (it very slightly differs in longitudinal and latitudinal directions). The difference is around a tenth of a percent.

Of course, there are other effects that play a role - namely the refraction, but also waves or tide. You can read a very detailed information about horizon at WikiPedia. An the curvature of the Earth is described there too in this article: https://en.wikipedia.org/wiki/Figure_of_the_Earth