Is Russia’s S-400 a Real Air Force Killer or a Paper Tiger?

By Charlie Gao,The National Interest

In March 2019, the Swedish Defense Research Agency (FOI) published a report that alleges that Russia’s vaunted Anti-Access/Area-Denial (A2/AD) capabilities in the Baltic region are overrated. It presents a technical and doctrinal argument for why Russian long-range missile capabilities, in the anti-air, anti-ship, and anti-land realms, may have been overstated in the media and in professional analysis.

One of the key systems the paper takes aim at is the Russian S-400 air defense system. It suggests that analysts in media have overblown the threat the S-400 poses by taking claims about its range at face value, namely the 400 km figure for the 40N6 missile, and by overstating the S-400’s ability to engage incoming missiles meant to suppress or kill it.

In order for the S-400 to have a 400 km range against large aircraft, it must be able to see over the “radar horizon” presented by the curvature of the Earth. There are a couple solutions to this, which are gone over in the paper: namely the use of an over-the-horizon (OTH) radar or through cooperative engagement capability (CEC). CEC, in this scenario, would involve using data from airborne warning aircraft to fire surface-to-air missiles.

The FOI authors of the paper state that current OTH radars cannot guide a missile effectively, citing a 2016 War is Boring article by David Axe and a Swedish paper regarding OTH radars. The 2016 article states that early low-frequency radars could only pinpoint a target’s position to 10,000 feet or so, which isn’t accurate enough to guide a missile.

It is possible to lob 40N6 missiles out that far at approximate tracks generated by OTH radars and then rely on the active radar seeker on the missile, which has a range of around 30 km, to guide the missile finish the job. The paper acknowledges this capability, but dismisses it as inaccurate as “V-2 strikes”. However, depending on the kinematics and seeker capability of the S-400 missile, this capability could be a very real threat for large aircraft.

Airborne warning aircraft provide far more accurate tracks. Russia fields over twenty A-50M airborne warning aircraft, which can detect aircraft out to 800 km, far beyond the range of the S-400. The sticking point here is the networking required: the airborne warning aircraft needs to send data to the S-400 system, which then uses that data to engage the plane at range. Russia has not discussed nor demonstrated this capability, and the FOI paper states that acquiring it is very hard.

But, Soviet MiG-31 interceptors were known to possess similar capabilities during the Cold War, albeit solely in the air-to-air realm. They were able to pass track data and transfer missile guidance from one MiG to another. It was also possible to dump engagement data to ground stations, although the extent of that is not known. This suggests that Russia could develop CEC rather rapidly if required, though the air-to-ground data transfer may pose significant difficulties.