Ukraine Has a Breakthrough Problem

Foreign Policy, 03.08.2023
Barry R. Posen, profesor de ciencia política (Massachusetts Institute of Technology)
  • Military history suggests Ukraine’s current campaign is far more daunting than the public understands.

It is the stated policy of the Ukrainian government to retake all of the territory that Russia has seized since 2014, including Crimea. To achieve this goal through military action, the Ukrainian military must accomplish one of the most daunting of military tasks: It must break through dense, well-prepared defensive positions, find some running room, and then either move quickly toward an important geographic objective such as the Sea of Azov, hoping to unravel the remains of the defending Russian army along the way, or quickly attempt to encircle a portion of Russia’s sizable forces in hopes of annihilating them.

To fail at this kind of campaign will mean that Ukraine is likely destined for a long war of attrition—an inauspicious one, pitting it against a much more populous country. Ukraine naturally wishes to avoid the attritional war by succeeding at its breakthrough campaign. But military history suggests the challenges here are also more daunting than have been commonly understood—at least among the public in the West.

The breakthrough problem emerged during the First World War, when European countries first became rich and populous enough to defend very long fronts—in some cases nearly their entire borders. They were assisted in this effort by vast improvements in firepower, including range, rate, accuracy, and lethality, which augmented the typical advantage that defenders have: the ability to choose the terrain on which they will fight, to construct fortifications, and to arrange their forces in ways that allow the most effective use of firepower—for example, by ambushing.

The perfection of the tank, fighter aircraft, and radio allowed skilled attackers to overcome defenses early in World War II, but over time, defenders found ways to employ the same assets. The mobility of armored forces allows the defender to rapidly move reserves to whatever segments of its defense seem in greatest danger of collapse. Assuming a reasonable air defense, the lateral movement of armor behind one’s own lines is vastly easier than the offense’s forward movement of armor against a defended position. The defense added the mass employment of anti-tank and anti-personnel land mines to its bag of tricks, which U.S. analysts concluded shortly after World War II had been very cost-effective as anti-armor weapons, accounting for as much as 20 percent of all tanks damaged by enemy action.

Though cinematic representations of World War II seem to portray a more fluid battlefield than World War I, both wars degenerated into brutal and bloody attrition slugfests. As in the First World War, soldiers on all sides groped for ways to cut through the defense, restore mobility, and maneuver to the battlefield. Ultimately, they found ways to do so, though only after much hard fighting, and usually only after mustering vast material superiority. A military rule of thumb emerged that at least a 3-to-1 advantage in combat power is necessary to have a reasonable chance of success against a well-crafted defense.

But attackers must do much more than organize material superiority. The defender must be rendered thin at the front so that it loses coherence after some initial fighting; its tactical reserves much be degraded through prior action, delayed during the fight, or simply defeated as they appear; and its operational reserves must also either be degraded in advance or diverted to other tasks by deception or supporting attacks, or also defeated as they appear. All of these tasks need to be integrated and synchronized, no mean feat for any army.

As of this writing, we can observe, to the limited extent the combatants allow, Ukraine’s efforts to address some of these issues—mainly, the problem of an initial breach. As is now known to all, the Russians have prepared a dense and well-constructed defensive system. Minefields, deep anti-tank ditches, and concrete obstacles slow the attacker. Dug-in defenders, some in earthworks and others in concrete bunkers, cover these obstacles with direct fire from machine guns and anti-tank missiles. They are likely augmented by tanks and armored vehicles firing from their own dug-in positions. Defensive combat vehicles frequently move among multiple prepared positions to elude the offender’s suppressive fires. Artillery fire from the rear allows for sudden concentrations of large numbers of shells and rockets on the attacker, sometimes with cluster munitions. The attacker must clear minefields and eliminate other obstacles while under observed fire. It is often stalled while doing so, and thus the defender’s fire is very effective. The attacker may have to move despite the presence of mines, and thus the mines extract their toll.

We have also seen that Russian attack helicopters function as very mobile tactical reserves. When a Ukrainian unit is hung up on an obstacle or minefield, helicopter-fired missiles augment the local Russian defenders. Because of the low altitude tactics that the Russian flyers probably employ and the range of their anti-tank weapons, these helicopters are very difficult for ground-based air defenses to engage.

Obstacles and fires thus work together to slow and ultimately destroy attackers. Reports from the fighting suggest that the very best Western armored vehicles in these fights—Leopard II tanks and Bradley Fighting Vehicles—have suffered significant damage in their attempted attacks. The only silver lining for Ukraine is that the crews and infantry squads tend to survive the vehicle damage, a tribute to Western designers. But this is not enough for the offensive to succeed. For a successful breakthrough, the vehicles themselves need to be able to move forward, taking their firepower into the depth of the enemy’s positions.

Historically, defenders have been rendered thin through two measures. The most straightforward is prior attrition, supplemented by the immediate shock of truly massive offensive firepower. The attacking force just fights the defender for a long time, accepting high costs, and bets that the defense cannot replace their losses at the rate that the attacker can.

This is what the Allies did during the Second World War as they fought the Germans. Over time, German combat power was simply worn away, mostly in fighting at the front, but also as a result of allied bombing. Greatly superior in combined population and industrial power, the U.S., the Soviet Union, and the British produced many more weapons and fielded many more units than the Nazis. The German army’s best efforts to maintain a coherent defense, backed by mobile reserves, simply failed due to lack of sufficient resources, though it took quite a while for the Allies’ tactical acumen to catch up with that of the Wehrmacht.

Sheer destruction was also a crucial Allied tool to achieve the final thinning of the defense. When breakthrough efforts were launched in the West, the U.S. and the British combined massive artillery fire with concentrated bombing strikes. The Soviets in the east did the same, though they relied more on their artillery than on their air power.

It does not appear that Ukraine’s suite of artillery, rocket launchers, and drones is quite up to this task, but only the unfolding campaign can answer this question. And though Ukraine hopes that the West will soon supply it with fighter aircraft, U.S. experience in the Desert Storm operation against a far less capable adversary than Russia suggests that the number required both to suppress the Russian air defenses and then attack the Russian ground forces in depth is far in excess of any figure thus far suggested.

The other way to render the enemy forces thin on the ground is to surprise them on a stretch of front that, for their own reasons, they have left thinly defended. This is what the Germans did against the Americans in the Ardennes Forest in December 1944 in the Battle of the Bulge. The United States and Britain did not have sufficient forces to sustain offensives all along the front. The United States used the  hilly and forested terrain of the Ardennes, considered more defensible, to achieve an “economy of force.” Not only did they cover the front at a density half of what their own doctrine recommended, but they also used the Ardennes as what historian Charles B. MacDonald later called a “nursery and old folks home,” breaking in green divisions new to the theater and providing a space for veteran divisions that had suffered unusually high attrition to recover their strength.

German intelligence figured this out, and careful camouflage and deception allowed the Germans to concentrate a very large force in the sector without U.S. detection, achieving a favorable overall force ratio of perhaps 3-to-1. Initially, the Germans enjoyed some success, but their inability to defeat Allied tactical and operational reserves, and to fully resupply their forward elements, eventually caused them to break off the attack.

The Ukrainians found a thinly held section of the front in their successful offensive in the Kharkiv Oblast in autumn 2022. The Russians had taken sufficient losses earlier in the year that they needed to economize somewhere, and they did that in Kharkiv. Ukrainian intelligence figured this out, and either managed to surprise the Russians, or the Russians simply chose to accept the loss. Though their withdrawal looked like a rout, they avoided the capture or destruction of most of their units.

The Ukrainians have, no doubt, hoped to repeat the Kharkiv experience in their summer 2023 counteroffensive, but as of this writing, success is still elusive.

On first appraisal, Russian forces in Ukraine do appear thin on the ground, which has fed the hope of successful offensives. By my count, the Russians started the war with perhaps 40 brigades. Some have been battered, and most have suffered high attrition, but the Russian reserve troop mobilization in the autumn of 2022 seems to have allowed them to restore their fighting power. But even if we assume that they are again at full strength, at best, the Russians can only defend the entire 1,000 kilometers (more than 600 miles) or so of front by using every brigade with no reserves—and even that may be a stretch. During the Cold War, analysts would have said that 15-20 km (about 9-12 miles) is about the most a brigade can defend successfully, even for a short time.

But modern technology—including drones, advanced artillery and ground-based rocket systems, and long-range, anti-tank guided missiles—allows defensive units to take on bigger tasks than their forbearers. The Ukrainian army’s offensive success in fall 2022 has also paradoxically allowed the Russians to shorten their lines, and thus eased their defensive task. The destruction of the Kakhovka dam in southern Ukraine made the south easier to defend, permitting a further consolidation of Russian combat power.

The Russians may also have added additional combat units to their forces in Ukraine. Ominously, Gen. Christopher Cavoli, the U.S. supreme allied commander Europe, declared in April that Russian forces in Ukraine were stronger than they were at the outset of the war. He offered no figures, but I have heard numbers as high as 300,000 troops, compared to 200,000 at the outset of the war. If true, then Russia probably has deployed additional brigades to Ukraine, improving Russia’s ability to maintain tactical and operational reserves.

Some Western experts suggest that the Russians are devoid of reserves, but this would imply that the Russians are still the military amnesiacs that they were at the outset of the campaign. The Russians have been fighting effectively now for months, however, so they must have remembered something from their old manuals and practices, and they too have managed to exploit new technology. If Western and Ukrainian intelligence believe there are no significant Russian reserves, that would explain both Ukraine’s determination to continue its efforts to gnaw through Russia’s defensive positions and Western military declarations of confidence in the offensive. They can still hope ultimately to crack the first line of Russian defenses, restore mobility to the battlefield, and unhinge the remaining Russian forces.

If this assumption is wrong, however, then there is probably little point in Ukraine continuing current efforts, because even if it penetrates deeply into Russian-held real estate, it will likely meet significant Russian counterattacks, under the worst possible circumstances—with its own forces weakened by attrition, strung out and scattered by virtue of the prior battles, and probably undersupplied. At that moment, the Ukrainian forces may also be beyond the range of some of their own supporting drones, artillery, and rockets, upon which they have come to rely, and which now, due to Russian jamming, seem less effective than they once were.

Such a dire outcome is by no means certain, but the problem for Ukraine is that it will have no experience to draw upon if this possibility unfolds. And because its air force is small and largely committed to defense, air power cannot rescue the Ukrainians. They will be on their own. Though the Russians have not demonstrated a lot of skill at mobile operations in this war, nor shown much of an ability to improvise, they have improved over the course of the conflict, and it is not beyond the realm of possibility that they are waiting for their moment.

The Ukrainians are still in the early days of their summer offensive. As of this writing, they are grinding forward in what appears to be one major offensive aiming for the Sea of Azov and a supporting offensive around Bakhmut. If these efforts begin to gather momentum, they may nevertheless still have two important problems to confront—Russian tactical reserves deployed in their path to break their momentum, and Russian operational reserves that may gather for counterattacks into the lengthening Ukrainian flanks. Russian air power, which has been much more successful at ground attack in recent weeks than it was early in the war, can further slow the Ukrainian advance by striking both combat units and logistics.

It is likely that these problems have been analyzed during war games with NATO advisors, and solutions have probably been devised, at least in theory. But history suggests these are very demanding operations in terms of materiel, planning, and military skill. Facts sufficient to make an educated guess about Ukraine’s odds of success are few. But observers should not be surprised if this offensive peters out with, at best, a partial success.

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