Holy,  a first strike only works if the targets are still there when the warheada arrive.  Since it takes 15-30 minutes for a submarine launched ballistic missile to reach its target, it is highly unlikely that silo or aircraft based weapons will still be there.  Launch on warning is the strategy to prevent your weapons from being destroyed by the first strike.  Russian maintenance tends to be worse than American,  so it is uncertain what percentage of their silo based missiles, bombers and submarines will actually work when ordered to launch.