Here's What You Need to Remember: 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.

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.

The report may also overstate the ease of knocking the S-400 system out. In discussing countermeasures to the S-400, the article states that a S-400 battalion could engage between sixteen and sixty-four targets before having to reload, depending on the mix of medium-range and long-range missiles loaded into the launcher. From this, they state that a saturation attack with “dozens” of precision guided stand off weapons and decoys could take out the S-400’s engagement radar.

While “dozens” is an approximate figure, this analysis ignores the presence of point defense missiles near the S-400, and the S-400’s ability to reject decoy targets.

Earlier on in the paper, the FOI authors acknowledge that S-400 battalions are often deployed with Pantsir-S1 point defense systems. They largely dismiss the effectiveness of these systems, citing examples of the systems easily being destroyed by Israeli attacks in 2018 and 2019.

However, in Syrian service the Pantsir was operating independently: relying on its own search radar to detect targets. When operating as point defense for the S-400, the Pantsir can receive track data from the S-400’s more powerful search radar, although it still must use its own fire control radar to engage targets. This may allow it to be more effective than it was in Syria against Western precision guided munitions. Russia is also working on new, smaller missiles to arm the Pantsir, so it can prosecute more engagements without reloading and be more effective in the face of swarm or saturation attacks.

In addition, it’s possible that Russian forces may deploy the more effective Tor point defense systems to augment the point defenses of the Pantsir, following the Syrian performance. Tors are known to be fielded in Kaliningrad, as are S-400s.

The S-400 also has the capability to perform non-cooperative target recognition (NCTR), although there is little open data on this capability. From this, it may be able to classify some oncoming targets as decoys to avoid wasting ammunition on them.

As a result, it may require more missiles than the report suggests to fully knock out an S-400’s engagement radar, although any system can be saturated.

Overall, the FOI paper presents good analysis by showing that the Russian A2/AD anti-air bubble is not as big as people might think. But they might be selling the S-400 system a little too short. Russia has had a limited form of CEC for decades, and the Tor is a formidable point defense system.

Information about MiG-31 CEC was taken from Авиация ПВО России и научно-технический прогресс: боевые комплексы и системы вчера.

Charlie Gao studied Political and Computer Science at Grinnell College and is a frequent commentator on defense and national security issues. This article first appeared last year.

This article is being republished due to reader interest.

Image: Reuters.