Some time ago the news broke that the upgrade program for the US MGM-140 ATACMS-missile will include not only a near-doubling of the range past 300 km, but also a seeker head allowing the targeting of moving targets at land and sea.
Much focus was placed on the last part, as it signifies an important shift in how the US Army sees its mission, with this being the first stated anti-shipping capacity of the force since disbanding the Coast Artillery Corps over half a century ago. In reality, hitting a moving target on land is probably a harder engineering problem than hitting one at sea, as the sea provides a level background made up of sea water which is nicely homogeneous when it comes to its temperature, refractive index, and differential scattering coefficient. Compare this to land, which is made up of a bewildering variety of rocks, swamps, concrete, forests, roads, cities, deserts, snow, and what not. In short: if you can identify, track, and target a moving target on land, doing so at sea is rarely an issue.
Exactly how the revised ATACMS will do its targeting is still unclear, but my best guess would be an IIR-seeker, allowing the missile to make (small) course adjustments on its way down towards the target.
For Finland, this provides an interesting opportunity, as Finland operate the M270 MLRS, the launching platform of the ATACMS (though not the missile itself). Wouldn’t this then provide an opportunity to get two capabilities for the price of one?
The answer, when actually on the battlefield, is ‘No’.
The M270, or 298 RSRAKH 06 as it is known locally, is a key part of the Finnish Army’s indirect firepower. Mounted on a chassis based on that of a M2 Bradley, it is highly mobile off-road and able to keep up with the advancing armour columns. Their mission according to Finnish doctrine is to support the manoeuvre elements of the army at the schwerpunkt. In this role, their tactical and (to a somewhat lesser extent) operational mobility shines, and the (arguably light) armoured nature makes it able to take some enemy fire and still keep on fighting.
By contrast, a shore based anti-ship missile system usually downplays vehicle protection and tactical mobility for a higher payload and strategic mobility. Hence the vehicles used are often heavy trucks, keeping mobility higher and operating costs lower compared to tracked vehicles. As such, the M270 is far from an ideal launching platform, running around in a tracked and armoured chassis while sporting a maximum of two missiles.
The nature of the missile is also not without limits. As said, exactly how the seeker and guidance system will function is still unclear, but most likely the missile will have a relatively narrow engagement cone. This is partly offset by the faster travel time compared to a traditional sea-skimming missile, but it will still require a more exact location fix on the target. Granted sea-skimmers also benefit from an exact fix, but they can also be employed for more general modes of operation like launch on bearing. However, the biggest limiter is where to put the just 20+ launchers available to the army?
As noted above, they will be travelling with one of the two mechanised battlegroups. If they happen to be south of the Seinäjoki-Joensuu line (approximately 63°N) they are technically able to perform the anti-shipping mission in the Gulf of Finland. In practice the dual-tasking would be harder to pull off. The army would, quite rightly, insist on them carrying the load most suitable for the indirect fire support task and having the launchers subordinated to them. If the Navy would locate a suitable target, they would then have to call the battlegroup and ask for permission to use their rocket launchers. They would then have to hope that A) the launchers were available, B) in a suitable location to fire upon targets in the Gulf of Finland, C) that they were loaded with ATACMS, and D) that the battlegroup commander would not prefer to keep his high-value launchers hidden. If all of the conditions were met, the attack could be made. However, a typical high-value naval target would require a higher amount of missiles compared to a typical ATACMS target, such as a key bridge or other installation. This is due to the naval vessel seldom sailing alone, and sporting a very potent and concentrated anti-air cover (especially if it indeed isn’t sailing alone).
Is the anti-ship ATACMS a bad idea? Not necessarily. It does offer a new angle of attack (quite literally), as well as being hard to counter due to its speed. A more interesting question is which moving land targets that the US Army is planning on hitting with a one million euro a piece missile from a few hundred of kilometres out? Trying to take out individual vehicles will rarely make sense, though it could be the case with e.g. long-range SAM systems which are few and far between. In this, the enhanced ATACMS could be a part of the answer to the growing A2/AD-threat.
If the missile is operated in an anti-shipping role, the more mobile HIMARS would probably be a better launch platform. This would then only carry a single missile per vehicle, but would be cheaper to operate and provide the kind of operational mobility needed for coastal defense systems. For Sweden, where the main threat picture include an amphibious assault in the south-eastern parts of the country, HIMARS coupled with ATACMS could be a solution. The Swedish Defense Forces currently lack both a multiple-rocket launcher system and a shore-based anti-ship missile system. Crucially, they also lack funds for a number of other things, and it is unlikely that they would get the funding to procure both systems. Here the HIMARS actually could make some sense, in providing anti-shipping capability with the ATACMS before the enemy has gotten ashore, and indirect fire support with rockets once the battle fore the beachhead has started.