The Russian S-400 (also known as the SA-20) is one of the newest air-defense systems in the Russian military’s inventory. This system actually consists of two missiles: A “big” missile with a range of 400 kilometers, and a “small” missile with a range of 120 kilometers. The system is an improved version of the S-300 (Cold War era SA-10 Grumble), and uses the same transporters as the Grumble. The “big” missile is intended for use against targets over the horizon from the launcher. For this, read planes like the E-3, EA-6B, and KC-10. These are support assets that are often required for successful air campaigns. Going after these planes with fighters has not worked – the American fighters are usually flown by better pilots, and usually can shoot down attackers quickly. Just ask the Iraqi and Yugoslavian Air Forces. The SA-20 is intended to be used instead.
Interesting if true. How to do detect a plane at 400km with a ground based radar? Put it on a mountain maybe...