[RayChuang88]

I wonder did the Russians design the S-400 to be equipped with an enhanced radiation low-yield nuclear warhead of around 2-4 kT. There's a reason for such a warhead: knock down incoming SLBM/ICBM warheads at altitudes up to 65 km above the ground, which means the S-400 becomes a mobile ABM system that can be quickly deployed around major Russian cities in case a world war is imminent.

[PIF]

Their early versions had .5 kt warheads for intercepting US ICBMs. The US, under Nixon, allowed them in Anti-Ballistic Missile Treaty , I believe. We, naturally, got rid of our missile versions under the same treaty. As well as anything else that the Russians and Nixon considered a dangerous nuclear devise ... and so much for going to the stars on nuclear powered rockets ... when America died by Richard Nixon, the man who terminated the USA with prejudice.