Nuclear submarine boats would survive almost all first strikes. If there is a new arms race, unfortunately it will spread to low orbit. The MIRVs are probably

Nuclear submarine boats would survive almost all first strikes. If there is a new arms race, unfortunately it will spread to low orbit. The MIRVs are probably to try to overwhelm likely missile defenses. A nuclear strike of that magnitude would be suicide for the attacking nation however with fallout, climate change, and economic disruption. But considering both Russia and now China are being run by full-on autocrats... that's not good.