‘Carcinisation’ is a term in evolutionary biology used to describe the rather bizarre tendency of many fairly distinct branches of the animal kingdom to have convergently evolved into crabs. Charting the evolution of armaments, much the same convergent evolution seems to be happening, where numerous, and often very different, munition families are increasingly becoming more like cruise missiles.

The exact form this process takes depends on the weapon class and role, but broadly speaking, many different classes of weapons are increasingly adopting various characteristics of the cruise missile format. These characteristics include jet engines and wings to provide sustained powered flight at medium-high speeds, along with increasingly sophisticated sensors and guidance mounted on the projectiles themselves. Some are even moving from being single-role to multi-role. The result is that many of the latest examples of armaments are now not so dissimilar to cruise missiles. Table 1 shows some examples of this evolution taking place in several different classes of armament.

As the table shows, evolutionary progression isn’t completely evenly distributed; tube artillery for instance still has a ways to go before its munitions become truly ‘cruise-like’. Other cases show that not all weapons start from the same baseline – one-way attack (OWA) unmanned aerial vehicles (UAVs) for instance were already effectively a ‘poor man’s cruise missile’ from conception, and have only steadily shifted further in the direction of becoming more cruise-like, with recent examples such as Geran-5 being virtually indistinguishable.

It is also worth explicitly noting that being more cruise-like doesn’t necessarily mean a particular weapon is better or ‘more advanced’ than another. A Roadrunner-M for instance is always going to be less well-suited to shooting down fast jets than an AIM-120, simply owing to the colossal speed differential and range of operating altitudes between the two. Yet it should also be understood that a lot of recent cruise-like weapons represent early explorations of this concept, and substantially more capable versions are likely to emerge within the near future.

So then why is the cruise-like format particularly favourable in the current operational environment?

Why cruise missiles?

As with evolution in the animal kingdom, there are environmental selection pressures on the evolution of armaments, from cost, to industrial scalability, to battlefield utility. Successful designs and adaptations end up proliferating, being mimicked and iterated upon; unsuccessful designs end up being discarded. Likewise, when a particular design proves successful and begins to proliferate, countermeasures to it soon emerge, both tactical and technical, which, depending on their success, then shape the future operating environment and set the direction for further adaptation and evolution. Sometimes, ideas can emerge ahead of their time, and get shelved for cost or practicality reasons, only to come back into vogue much later, once technological, operational, or economic barriers have fallen to the point where they become viable.

Looking at the transformations to technology and operating conditions over the last few decades, the main drivers pushing the ‘cruiseification’ trend forward would seem to be:

The long range advantage: Being able to out-range an opponent has always been advantageous. Today, however it is arguably more practical to do so, and more useful than ever.

Modern battlefields are sensor-rich, highly networked operating environments, under constant surveillance from drones, satellites, radars, and electronic signals intelligence (SIGINT). In this kind of environment, it is very difficult to remain hidden, and having numerous high-quality, networked distributed sensors creates a lot of targeting opportunities. This situation incentivises weapons design to take advantage of this abundance of targeting data, and one of the most effective ways of doing this is to increase weapon ranges. Additionally, since the situation is similar for both sides in a peer conflict, there is additional incentive to out-ranging one’s opponent.

Beyond the obvious advantage of greater survivability for the shooter, long range weapons also allow logistics units to operate further back from the front, greatly decreasing the likelihood of their discovery and destruction, as well as decreasing the vulnerability of stockpiles in theatre by allowing them to be held further back.

Yet there are many ways to make a long-range weapon, and both sides of the War in Ukraine have shown that propeller propulsion can be perfectly viable for the long-range precision strike role. So why jet engines in particular? Why not simply stick with propeller propulsion?

Speed is beginning to matter more:  The ‘low and slow’ advantage previously enjoyed by drones and loitering munitions is disappearing, because industries across the world have developed effective solutions to the problem.

During the late-2010s and early-2020s, air defence systems, especially older models that were never designed with the drone threat in mind, tended to face difficulties with detecting and tracking many kinds of drones, particularly smaller drones. Perhaps the case in point here is the 2020 Nagorno-Karabakh War, in which Azerbaijan’s drones achieved considerable success against the ageing air defence systems in the inventory of Armenia and Republic of Artsakh.

This was due to a combination of factors. In the case of speed for instance, drones could sometimes fly so slowly that they would be filtered out by an older radar’s speed gate. Or a drone might be constructed from materials which are either radio-transparent, or less-readily reflect radar signals, such as fibreglass or plastics, equating to a lower radar cross section (RCS). For older radars designed to target Cold War era fast jets, this could result in returns below the radar’s noise floor, or dismissed as spurious. Additionally, drones could also be quite low-flying, allowing them to practice terrain masking in suitable terrain or sometimes (in conjunction with slow speeds) resulting in their radar returns being rejected as ground clutter.

Yet a lot has changed since 2020. Sustained investment into anti-drone technologies the world over has resulted in substantial improvements to the ability of radars to reliably detect and track even very small drones. This has been coupled with investment in low-cost weapons designed to engage such drones.

Thus in the new operating environment, faster, jet-powered projectiles are more survivable against adversary air defences than slower, propeller-powered models. This applies in particular to many dedicated anti-drone solutions designed with the ‘low and slow’ threat in mind – a case in point being the ‘pseudo-SAMs’ (interceptor FPV drones) developed by Ukraine. Dealing with faster threats will require faster interceptors than ‘pseudo-SAMs’, which tend to be more expensive and more difficult to produce at scale.

But if speed matters so much, this raises a further question. Rocket engines are even faster than jet engines, and fast rockets can be very difficult to intercept, so then why isn’t everything becoming a ballistic missile?

A specific mix of characteristics is favoured: Rocket engines are indeed faster than jet engines, and high-speed rockets can be very difficult targets to intercept. Yet jet engines have a number of characteristics which make them more useful than rockets in a wide range of operational scenarios.

A case in point is ballistic predictability. Any purely ballistic weapon, from tube artillery to ballistic missiles has to follow an arcing ballistic trajectory, so once the projectile is detected, the trajectory can be computed by a modern radar fairly easily, giving both the predicted impact point, as well as the launch point. In the case of tube artillery, this leaves the shooter vulnerable to counter-battery fire. In the case of ballistic missiles, the high, arcing path means the projectile can be detected fairly readily, giving warning time for the defender to respond and attempt interception.

Switching to jet propulsion essentially solves both issues. Jet propulsion provides constant thrust, giving its associated projectile a very high divert capability which effectively negates the possibility of ballistic predictability, thereby giving the defender less information about the launch or impact points. Jet propulsion also allows the projectile to attain high ranges while flying at much lower altitudes than a ballistic weapon of similar range, decreasing average detection ranges and so complicating interception.

Lower-altitude flight can also give the projectile utility in a secondary intelligence, surveillance, and reconnaissance (ISR) role. While this point may seem somewhat confusing when considering how today’s typical cruise missiles work, it begins to make more sense when considering how loitering munitions are used today, both for reconnaissance and strike. There is no reason this secondary role seen on loitering munitions cannot be carried forward to the new generation of ‘cruiseified’ weapons – and indeed some recent adaptations, such as the use of Geran-2 UAVs, which are already a ‘poor man’s cruise missile’, as launch platforms for smaller FPV drones to engage targets of opportunity, point to this thinking already being applied on the battlefield.

A further advantage is that wings and air-breathing engines allow a projectile to attain longer ranges than rocket propulsion for a given mass (at least while the munition remains in the endoatmospheric realm; beyond that, the rules change). This allows cruise missiles to be more compact than a similar range and payload class ballistic missile, which in turn means they can be deployed from a greater range of platforms.

Finally, constant thrust, and so high divert capability, are particularly useful when it comes to engaging mobile targets, particularly distant ones. For example, let’s examine the scenario of a battery of multiple rocket launchers (MRLs) such as 9A54 Tornado-S launching their salvo and then quickly repositioning. Given the typical ranges at which such weapons operate, it becomes it becomes very difficult to engage them after they have moved unless you use a weapon which can independently locate them and divert course to engage them. Fast jets could certainly work, but then they risk attrition to enemy air defences. The lower-risk response in this scenario would be to use a cruise-like projectile with the endurance and sensors to independently locate and engage mobile targets.

As an aside, some of these same characteristics are also behind the recent push to adopt hypersonic glide vehicles (HGVs). While many consider high speeds to be the main selling point of HGVs, this is not really the case. Nearly all ballistic missiles beyond short-range are already hypersonic, especially at the longer-range end of the scale. Intercontinental ballistic missiles (ICBMs) for instance tend to have higher average speeds than HGVs, and although they have to physically traverse a longer distance owing to their ballistic trajectory, they can still arrive on target sooner if launched on a depressed trajectory rather than a minimum-energy trajectory.

Alongside this, while objectively not particularly low-flying, HGVs nonetheless fly significantly lower compared to ballistic missiles in the same range class. This means lower average warning times for the defender. Additionally, the fairly high divert capability of HGVs compared to typical ballistic missiles also makes them ballistically unpredictable. These characteristics taken together can significantly complicate matters for the defender.

The democratisation of precision: As a final factor, the consumer electronics market of the past two decades has seen an explosion of low-cost but good-quality sensors, antennas, processors, and software. This has made building precision weapons easier than before.

Several decades ago, a high-end digital camera with automatic target recognition capability represented a major technical hurdle. Today, the technology exists in every smartphone, and can be bought for a fraction of the cost of many weapons. On top of this, multiple communications service layers have been built, from LTE high-bandwidth mobile communication technology, to satellite constellations such as Starlink, all of which have already been used for communications, targeting, and guidance on the battlefield.

All of this has not only accelerated the creation of the aforementioned sensor-rich environment, but has also greatly lowered the economic and industrial barriers to entry, procurement, and fielding of cruise-like weapons.

An evolutionary end goal?

As shown, the aforementioned factors are incentivising the development of cruise-like weapon designs, because these are particularly well-suited for the conditions of the modern battlefield. Do cruise missiles therefore represent some kind of ‘evolutionary end goal’ for weaponry? Probably not, but many of the operational factors driving their design are likely to remain relevant for a long time to come, and the cruise-like format helpfully bundles many of these useful characteristics together.

In terms of what comes next, a glimpse can be seen in the efforts of various countries to iterate upon the cruise-like format. Russia for instance, has several active technological branches relevant here, from Burevestnik – a cruise missile with a nuclear-powered engine aimed at providing nearly unlimited range; to the 3M22 Zircon – a hypersonic cruise missile (HCM); to Poseidon – while not really a cruise missile by virtue of being an underwater weapon, nonetheless can in some respects be thought of as a massive underwater cruise missile in role, at any rate more so than an underwater ballistic missile, as it has sometimes been referred to. All three effectively take aspects of the cruise missile formula, and try to push certain characteristics to extremes – whether range and divert capability (Burevestnik), or speed (Zircon), or payload and underwater capability (Poseidon).

Will the move to iterate on the basic formula by maximising certain characteristics be copied elsewhere? In some areas, such as speed, this is happening already with HCMs, and as for the others, it is difficult to say. What can be approached with more certainty is the range of countermeasures needed to combat the cruise-like threat.

What is the likely direction of counter-evolution?

With the march of armament evolution pointing toward the cruiseification trend continuing, what kinds of counter-adaptations would be needed to survive in this kind of operational environment? These adaptations do not necessarily have to be technological in nature, as operational and doctrinal changes can arguably influence the environment even more.

One promising approach right now would appear to be tweaking force design, to expand air defence coverage at all levels, and ensure that any systems chosen are able to cope with massed strikes. Under this model, reliability of interception and magazine depth are arguably more important than range. Long-range systems will still be needed to reliably engage higher-altitude targets such as ballistic missiles, since those threats aren’t going away. But to deal with the massed cruise-like threat specifically, it would be particularly useful to invest in a large network of very short/short-range air defence systems with low-cost interception means, located nearby everything the defender wants to keep safe.

Such measures could be anything from low-cost missiles, to automatic cannons, to high-energy lasers (HELs), to high-power microwaves (HPMs), to various ‘soft-kill’ measures such as jamming, spoofing or dazzling, to a blend of all of these. What is most important is that they are numerous enough to provide very good coverage throughout a theatre, so that assets can be permanently dedicated to specific points or formations the defender wants to keep safe. Alongside these should be a distributed sensor network capable of reliably detecting and tracking cruise-like threats throughout a theatre, providing both early warning and target cueing information to the nearest suitable means of interception.

For illustrative purposes, the aim would be to make the defended area resemble something conceptually akin to a map covered in bubble wrap, comprising a very large number of small ‘bubbles’ – zones defended by small, low-cost very short/short-range air defence systems, with very small dead zones in between. This basic arrangement should be supplemented by longer-range air defences to defend high-priority zones.

While cruise-like threats could attempt to bypass this kind of environment by flying higher, this would however come with the trade-off of making them more detectable to longer-range radars, and would not necessarily change the outcome, since they will still need to dive toward their targets eventually, and so may be intercepted in their terminal phase.

Another approach cruise-like threats could attempt is simply flying faster, as seen with HCMs. But this comes with some trade-offs. Firstly, HCMs are neither cheap nor able to be manufactured at scale quickly, meaning they will likely remain a low-volume threat. Second, HCMs tend to fly higher than typical cruise missiles anyway, to take advantage of lower air resistance at higher altitudes; and so would be remain open to detection and engagement by longer-range air defences. Third, HCMs will tend to slow down from their peak speeds somewhat as they enter lower altitudes in their terminal phase, as they encounter denser air, and because targeting and precision control is easier at lower speeds. During this phase, short-range interception could be possible with the right weapons.

While all the aforementioned provides some directions for thinking about the future path of evolution and counter-evolution for armaments, it is worth closing by saying that we do not yet know what characteristics will work best for tomorrow’s battlefield. Many of the latest development efforts are still very much experimental or theoretical in nature as regards their actual battlefield utility. The proof of their theoretical value will only be established through practical application; and as the War in Ukraine has shown numerous times, war has a habit of destroying beautiful theories.