Thanks, yes, the DOD must stay on top of it. But I personally see little threat from hypersonic missiles that can travel through the lower atmosphere at that speed. At a certain point, friction or heat can't be gamed.

The only difference between Russian missiles and U.S. missiles are their accuracy and ability to adjust their flight paths. All my life I've read about the "Russian Threat" in advanced weapons. None of it has materialized. I've seen no documented destruction of a Ukrainian target by a Russian missile traveling at Mach 4+ in the atmosphere.

Russia built some of the largest nuclear subs. One sunk, right when Putin started. No one buys Russian equipment because it's better than the West (except for some stuff that's partly made in Ukraine ;)) They buy it because it's the only alternative if they're not friends with the U.S. I'm not saying it isn't deadly, it most certainly is. I'm only talking about it in a technological comparison.

Common people make the jump between the tech in their phone to military tech, as if advances in one indicate advances in the other. Sure, there are many advances in computer control. But advances in the material science necessary for sustained hypersonic flight in the lower atmosphere?

I don't see it--from anyone. Mother Nature won't approve it and her word in thermodynamics is final ;)