Russia claimed that it had used hypersonic weapons to attack arms depots in western Ukraine on 18 March. Is this a qualitative up-step in Russia’s campaign, a sign of stress, or just a capability demonstration?

“Hypersonic” is generally accepted to mean a missile faster than 5,000 km/h (though there is nothing magical about that speed). Intercontinental ballistic missiles have always been hypersonic, exceeding 20,000 km/h, but they spend most of their journey from launcher to target in the near-vacuum of space, and only a few seconds passing through the atmosphere. The hard part is sustaining hypersonic speed inside the earth’s atmosphere, where atmospheric gases create friction, heating the missile to 1,000 centigrade.

At high altitude the atmosphere is thin and generates less friction and heat. But targets are at ground or sea level, so to remain hypersonic the missile must be constructed from materials which can withstand that heat. Heat is not the only problem. The air around a hypersonic missile becomes so energised that molecules lose their electrons and become ionised plasma, which makes terminal guidance difficult to achieve. Most of the investment in hypersonic missiles ends up in designing new alloys and in expensive and extensive testing.

Why bother? High speed offers three big wins. The first win is to reduce the time your opponent has in which to react to the threat. A low-level missile becomes visible to airborne radar at around 500 km. Flying at 900 kph a subsonic cruise missile provides about half an hour’s notice of its threat. In that time a ship can move 30 km, either off the missile’s incoming vector (leaving the missile’s pre-programmed search area) or away from the missile, potentially taking it out of range completely.

Targets are typically protected by layers of defensive equipment placed at progressively greater distances up-threat. The warning time of a subsonic missile allows the protective screen to manoeuvre to allow optimal engagement, to choose which defensive layers will engage which threats, to add air assets in the missile’s path which can attack the missile, and to deploy decoys and multiple active jamming solutions to force a soft kill – one in which the missile misses and splashes harmlessly.

With multiple layers of defence and multiple defensive options available, a well-equipped target force has a high chance of either forcing a miss or getting a hard kill on an incoming subsonic missile. That means the attacker must launch many missiles, preferably from many directions, carefully timed to arrive simultaneously and so to overwhelm the defensive layers. So subsonic missiles come with a high cost in units fired and firing platforms, and a demand a high threshold of accurate target data.

Hypersonic weapons fly at an average speed (from launch to impact) of around 3,500 kph. Detected at the same 500 km they cut the available reaction time from 30 minutes to about eight. That reduces target manoeuvre to +/- 8 km. Seen from the missile’s perspective the terminal seeker needs to scan an azimuth of only a couple of degrees either side of its track to gain a final target solution and a hit. Within that narrow arc there will be fewer false targets, fewer decoys and fewer SAM launches. The missile also conserves energy because it need only manoeuvre a degree or two off its base track, and that helps preserve both speed and range.

If the targeted force does not have airborne early warning cover the hypersonic’s win is much bigger. A warship with a radar antenna at 60 feet (18 metres) above sea level has a radar horizon to a sea-skimming missile (at 12 feet above sea level) of only 26 km (the high scanner of the UK’s Type 45 adds 10 km to that). A subsonic cruise missile takes 100-150 seconds to fly from its detection point at the horizon to the target. That is just enough time for the target to calculate the missile’s track, decide whether to engage it, to fire one or two surface to air missiles and for those to reach the incoming missile before it is close enough to do damage to the target ship. It also just allows time for decoys to be fired and to deploy, and for active jamming of the missile seeker to be programmed, aimed and used. An efficient well-worked-up ship should be able to counter most subsonic missile strikes.

A hypersonic cruise missile, even one whose terminal velocity has been reduced by drag and some evasive manoeuvring to perhaps 3,000 kph, covers the same distance in 30-40 seconds. If the target is quick enough to get a hard kill it must be obtained at sufficient distance that incoming missile debris falls into the sea instead of hitting the target ship at supersonic speed: three tonnes of missile fragments arriving at 3,000 kph can do almost as much damage as the explosive power of the warhead. Time is so short that there is barely time to deploy decoys and jammers.

While a well-prepared target warship has some chance of hitting a single incoming hypersonic missile, a salvo of two or three has a high chance of overwhelming the defence. If the target is not a modern air defence ship then it must rely on its own close-in weapon systems (chain guns or small short-range missiles) to get a hard kill, which will be at a range close enough for high velocity missile fragments to do damage.

When attacked by a subsonic missile a target can manoeuvre itself to present a smaller target aspect (turning towards or away from the missile at speed) or to change speed (and so throw off the missile’s predictive targeting algorithm) because there is just time to do that. With a hypersonic missile there is no time to use manoeuvre as a defence.

In sum, in a ship-killing role the use of hypersonic speed substantially reduces the number of missiles an attacker must fire to obtain a hit and, because of the kinetic energy of hypersonic speed, increases the damage caused by a hit.

At a strategic level the presence of hypersonic missiles forces one’s opponent to keep his naval forces concentrated and within constant airborne early warning coverage. That in turn means he must operate close to a friendly coastline, or within a Carrier Strike Group. Operations at a distance by ships sailing alone or in small task groups become borderline suicidal if a hypersonic threat is present.

Hypersonic missiles offer a third advantage, both at sea and on land. The target may well be covered by surface-to-air missiles located at some distance from the target itself. So at sea, an aircraft carrier is covered by air defence ships placed in a screen at several miles distance, and on land a target may be covered by a SAM battery located dozens of miles away at right angles to the incoming missile’s track.

If the defence unit is located off-track to the incoming missile its own weapon must close from the side of that track, which takes time. Surface-to-air missiles fly at twice the speed of a subsonic cruise missile, so can make up the ground from some way off. But they fly at half as fast as a hypersonic missile. Fired from several miles off the threat track, and literally at the last minute, they are more or less guaranteed to reach the hypersonic missile’s track after it has passed. The tactical result is that hypersonic missiles dilute air defence assets, by limiting the effective arc of fire of a given asset. In consequence some targets must be left undefended, or the number of targets must be reduced by concentrating one’s forces – both strategic wins for the owner of a hypersonic missile system.

There are major technical obstacles to getting a hard kill on a hypersonic missile. The defending missile is not designed to make a direct impact on the threat, as both are small and closing at extreme speed. The challenge is to make the 50-litre body of the defending missile get close enough to the 200-litre body of the threat missile so that a fragmentation warhead can get a hit.

The problem comes in two parts. First, one must design a guidance system that brings the two bodies together in time and space. Guidance (and radar tracking) systems use proportional geometry tailored to the speed of the threat – traditionally subsonic, but up to 2,000 kph for the well-established Moskit sea-skimming missile deployed by Russia since the 1980s – to steer the defending missile into the same few metres of space as the threat missile. A threat moving at two to four times the normal expected speed may render a tracking and guidance system’s parameters ineffective.

The second challenge is to detonate the SAM’s warhead close enough to the threat missile to get a hard kill. The kill is achieved by hitting the threat missile with one or more high energy metal fragments, either thrown in front of the incoming missile or from its side. Collision with a single metal fragment at that speed will break the threat missile up. To obtain that result the defending missile’s warhead fuse must be tailored to within a precise part of a millisecond. Detonate the warhead a millisecond too soon and the incoming missile will fly through a hole in the shrapnel field. Fire it a millisecond too late and the fragment field will bloom behind the incoming missile. Hypersonic missiles close at two to four times the relative closing speed of a subsonic cruise missile, which may allow them to outpace the fusing algorithm of the defending missile, even one detonated by a proximity radar system.

These two problems are solvable (THAAD has solved them) but a SAM system designed and built for a subsonic or low supersonic threat may need a substantial upgrade to beat a hypersonic threat missile. Some older systems will not be upgradeable at all.

Russia operates two tactical hypersonic missile systems and one strategic system.

Kinzhal (“Dagger”) is a re-purposed Iskander tactical ballistic missile (DoB 1980). The missile has kept its solid-fuelled rocket motor but is fired from an aircraft instead of from the ground. Starting high and fast, more of the missile’s fuel can be converted into range. Reports of range are ambiguous (varying from 500 to 2,000 km) and probably include the range of the launch aircraft. Russia is claiming that Kinzhal is both manoeuvrable and has terminal guidance (additional to its original inertial guidance system). Photographs of the missile in the public domain challenge both of those assertions, since the missile lacks wings and a visible seeker head.

Some steering will be provided by the small fins located in Kinzhal’s rocket exhaust, but these will only operate while the rocket motor is burning, at the start of the ballistic flight. Kinzhal may well not have the ability to carry out evasive manoeuvres in flight. Kinzhal’s most probable guidance system is inertial, to a pre-programmed target, aided by a satellite receiver but not by sophisticated manoeuvring systems. If that is true then it has no naval application unless fitted with a nuclear warhead. Kinzhal’s win over its ground-based sibling is that it can be fired from a much wider arc (in practice any air space that is safe for the launch aircraft) which forces an enemy to place more SAM systems around a given target, and so dilute air defence capability.

After leaving its launch aircraft the missile’s speed rapidly increases to high hypersonic. The missile’s trajectory is probably a low ballistic curve, in which the initial launch probably has a substantial “up” component. After motor burnout the missile will follow a ballistic flight path.

As its flight path descends through thickening atmosphere to ground or sea level the missile will slow down under friction. To maximise range the missile must spend as much time as possible as high as possible, where it is detectable at great ranges, and where it provides more time in which it can be engaged by defending missiles.

A high-altitude hypersonic missile is very like an incoming ballistic missile. The US has spent a substantial time and money equipping ships and shore-based units with THAAD – “Terminal High Altitude Area Defence” systems – which are capable of destroying high ballistic missiles at ranges of 100 km plus so long as they are flying more or less directly towards the THAAD launcher.

THAAD is not capable of hitting a missile on a crossing track, so each THAAD launcher is effectively locked to a target down-range and a threat up-range, both on a narrow arc. If the missile’s launch vehicle can fly around at will to change the threat bearing by 350 degrees THAAD risks becoming ineffective (unless the defender saturates the target’s defence with multiple THAAD systems or co-locates THAAD with the target. That increases the number of THAAD systems needed to protect a set of targets.

Russia’s second tactical hypersonic missile is Tsirkon (sometimes transliterated to Zirkon). Tsirkon has an air-breathing supersonic compressed air ramjet engine, usually abbreviated to Scramjet. A scramjet only starts to work well above supersonic speeds, so when Tsirkon is fired the missile must be boosted by a large solid-fuelled rocket motor. Designed to be fired at sea-level, Tsirkon has a shorter range than Kinzhal – 500 km has been demonstrated, and 1,000 km claimed.

Range is traded off against manoeuvring potential. Range is also a trade-off against average altitude. Tsirkon can climb to height for greater range and speed (at height it flies through thinner air) but at the expense of earlier detection. Exact range/height profiles are unknown but Tsirkon is designed to fly as a sea-skimming missile, reducing target reaction times to 40 seconds.

Tsirkon is reputed to have the ability to evade counter-missile fire. Two approaches are available. The first is to use conventional aerodynamic control surfaces to alter course. Tsirkon appears to have these but their use comes at a cost in speed, and the weight of actuators reduces the explosive payload.

A second approach is to use small manoeuvring thrusters which can bodily move the missile up, down or sideways in flight. If used at the precisely correct moment these can force incoming hard-kill warheads to miss by jumping Tsirkon out of the shrapnel path. A side-skip will also move Tsirkon out of the narrow beam of a targeted jammer. Lateral thrusters don’t slow a missile down and are lighter than aerodynamic actuators, which make it more likely that Tsirkon employs these than guidance surfaces. Videos of Tsirkon firings (and also of S400 firings) show such lateral thrusters in action, to orient missiles from vertical launch attitudes to horizontal flight attitudes.

A third type of hypersonic weapon, a hypersonic glide vehicle, has also been tested by both Russia and China. This is an unpowered gliding body which is carried into low earth orbit on a conventional ballistic missile. Once in orbit and at high hypersonic speed, either its on-board guidance system or a ground-based command trigger braking rockets, which bring it out of orbit to head for its target at high hypersonic speeds. Russia’s version is called Avangard, and has been tested several times. China tested its own version – the DF17 – last year to considerable Western consternation.

There is no public domain evidence that either weapon has terminal guidance, though claims exist that they can be guided towards a moving target, such as an aircraft carrier, using lateral and vertical thrusters.

Hypersonic glide vehicles could be used to attack critical ground-based infrastructure at continental ranges – imagine a US attack on a Russia/China oil pipeline in Mongolia. The US has invested several billion dollars in hypersonic weapon and glide vehicle development aimed at creating a weapon which can strike ground targets anywhere on the planet at very short notice, but so far nothing has been brought into service. US programmes include Conventional Prompt Global Strike, the Long Range Hypersonic Weapon and the Air Launched Rapid Response Weapon programmes. The US has also collaborated on hypersonics with Australia.

To summarise, so far only Russia has a working hypersonic anti-ship capability, and Russia and China working land attack capabilities. Russia’s (claimed) use of a hypersonic missile in Ukraine is probably largely symbolic, and possibly nothing more than an opportunistic operational test.

There are serious question marks over whether the reported Kinzhal strike in west Ukraine was actually in West Ukraine, or even a Kinzhal. Planetlabs has geolocated the target we see in Russia’s video as a farm in East Ukraine about 100 km south-east of Kharkiv, and has dated its destruction to a week before the date of the apparent strike. After the strike we see no secondary detonations, and the resulting fire has a single hotspot, consistent with unburnt fuel combusting, but not with burning ammunition stocks. The video does show (at two seconds in) a munition of some sort descending vertically onto the target at high speed. The weapon’s size is consistent with a Kinzhal – 4 metres long – but equally consistent with its ground-launched cousin the Iskander tactical ballistic missile. The blast, on the other hand, is inconsistent with a 500-kg high explosive warhead detonation.

With no maritime dimension to the Ukraine war Russia’s Tsirkon ship-killing missile is of little tactical relevance, though we may see symbolic firings of these too against land targets. Successful use of a Tsirkon against a warship would be a completely different matter, and a game-changer to compare with the destruction of the Israeli ship Eilat by a missile in 1967 – the first missile kill in modern warfare.