> There's a reason all modern silo based (and submarine) ICBMs are solids.

Believe it or not, here in 2026, this is incorrect!

Those crazy Russians:

https://en.wikipedia.org/wiki/R-29RMU_Sineva

https://en.wikipedia.org/wiki/R-29RMU2_Lajner

UDMH + nitrogen tetroxide.

I would not want to be a Russian submariner. For all sorts of reasons.

Do you need to be able to strike at a moment's notice?

For a proper MAD-based nuclear deterrence, yes, you want to be able to launch a massive retaliation while your enemies' missiles are still in the air. Submarine-launched missiles also require stable storage. But having first-strike capabilities, the ability to wipe out any city in the world in return for a few weeks' planning, seems like something militaries would find valuable.