When Russian forces invaded neighboring Ukraine on February 24, one of the first places they crossed into was the northeastern Sumy oblast. Thirty-nine days later, after intense fighting across the province, Sumy’s governor announced that all Russian forces had withdrawn from Sumy. Ukraine had won the battle. How?

Ukraine’s military had mounted a noncontiguous strongpoint defense of Sumy oblast. While static defense forces held strongpoints that centered on urban and other key terrain, light infantry roamed the gaps between these strongpoints. This combination—particularly the contributions made by the mobile light infantry—first delayed, then disrupted, and finally turned back key Russian supporting efforts along critical ground lines of communication. This effort, in both Sumy and the adjacent Chernihiv oblast, denied consolidation, resupply, and mass for Russia’s main effort to encircle Kyiv. Russia’s inability to secure its lines of communication through eastern Ukraine to its forward forces around Kyiv forced Russian commanders to divert troops and exposed their vulnerable road-based logistics to threat. Ultimately, this led to an operational shift in Russia’s focus from Kyiv to the eastern and southern theaters of the conflict, abandoning large swaths of territory Russian forces had tentatively seized in their thrust toward Kyiv.

For US ground combat forces preparing for operational environments fundamentally different from those of nearly two decades of America’s post-9/11 wars, the defense of Sumy highlights an important lesson. It demonstrates how mobile light infantry—armed with antitank guided munitions, supported by loitering and unmanned aerial vehicles, and with robust communication infrastructure—are key to a successful strongpoint defense against a combined arms attack on the modern battlefield. The defense of Sumy offers empirical evidence of this fact. But understanding why this is the case—and in particular why mobility, survivable platforms, and the right munitions are so important—requires an exploration of the concept of strongpoint defense, its evolution on the twentieth-century battlefield, and the unique ways in which Ukrainian defenders applied new and innovative approaches to the concept.

Drawing on the Lessons of History

Germany developed a concept of elastic defense in the closing years of World War I in response to the casualty rate it was experiencing and the German Army’s overextension in the face of renewed, massed offensives by the Allied Powers. By pivoting from the idea of holding every inch of ground, Germany was able to reduce the length of its front and build in redundancy in its defensive sectors to contain Allied breakthroughs at minimized loss. This became a prototypical defense-in-depth concept. The German defensive doctrine of elastic defense carried over into the next world war. Three pillars formed this defense doctrine: dispersal and depth, counterreconnaissance, and mission command flexibility.

A strong lesson Germany drew from elastic defense in the context of trench warfare was that “casualties, fatigue, and confusion debilitated assaulting infantry, causing the combat power of the attacker steadily to wane as his advance proceeded.” This very closely mimics what occurred to Russian forces in Sumy oblast during their penetration toward Kyiv. As forces penetrated they became slowed, distracted, consumed, and ultimately reduced in a series of limited, small-scale engagements from outposts to the layers of defensive positions and independent counterattacks.

In the interwar period, German defense doctrine and training evolved to address the threat of developing armor in the penetration, sparking a lively debate over whether to prepare principally for positional warfare or maneuver warfare, and if elastic defense was still appropriate. This seeded the Germans’ future adaptation of elastic defense into the strongpoint-centric hedgehog defense. This modification centered on the separation of the enemy’s infantry from its armored formations. If infantry could be separated then the tanks, “rampaging through the German defensive zones like rogue elephants,” were isolated and eliminated by specialized antitank elements. Ukraine took this further in the defense of Sumy. Beyond targeting and separating the infantry from the tanks in isolation, Ukrainian forces also took the fight directly to Russia’s vulnerable truck-based logistics. The effectiveness of Ukraine’s defensive approach was further amplified by Russia’s dearth of infantry forces. Russian infantry units were woefully understrength before they even made contact with the roving bands of Ukrainian fighters. With this thin line of infantry support, and Ukraine’s deliberate effort to target and separate infantry from the armor, the Russian advance was headed for exhaustion, disruption, and confusion, allowing the small, dispersed Ukrainian kill teams to target isolated and vulnerable armor in splintered combined arms tactical groups.

The German strongpoint defense concept emerged to mitigate a weakness. Whereas a desire to limit casualties in 1917 led Germany to modify its defense concept, in 1941–42, reversals on the Eastern Front against the Soviet Union led to new adaptation. This change emerged from Adolph Hitler’s December 1941 no-retreat/stand-fast order. Now German defending forces had to find a way to hold their extended frontage against massing Soviet Union offensives without the benefits elastic defense offered in shortening their lines to allow for the developed depth of redundancy. Where the strongpoint defense fell apart for Germany was in the Soviet mass ability to flood around the various strongpoints, bypassing, isolating, and leaving them behind to capitulate or be reduced by the less mobile Soviet follow-on forces.

Where the brutal weather, Hitler’s stand-fast order, and the overextension of their lines forced the Germans to concentrate around villages and turn them into strongpoints—villages that were naturally astride critical ground lines of communication like roads, bridges, and railways—they used this economy-of-force method to disrupt and hinder Soviet offensives, to a degree. In contrast, Ukraine applied a similar approach in Sumy, but one based on a more critical analysis. The Ukrainian response derived in part from a strong understanding of Russian doctrine, tactics, and methods. But it was especially enabled by the fact that, unlike the Germans on the Eastern Front, Ukraine was defending its homeland with its Territorial Defense Forces fighting for their homes, towns, and cities alongside the active forces of Ukraine’s conventional military. With these advantages on their side, the Ukrainian defenders went a step further than the Germans in World War II, focusing on denying the use of railroads, bridges, and roads to the Russian forces. This in turn had a significant impact on the overall assault on Kyiv to the west of Sumy. In short, tactical disruption in Sumy became operational disruption of the broader Russian aims in the northeastern theater. And it was achieved, as the Institute for the Study of War’s reports from March 3 to April 6 reveal, through a nuanced application of a modified strongpoint.

Of course, Germany’s hedgehog defense ultimately failed. As German commanders learned, strongpoints alone are vulnerable to encirclement and exploitation tactics of attacking forces. In Ukraine, invading Russian maneuver forces likewise sought to penetrate gaps between the Ukrainian strongpoints, bypassing them in their thrust toward Kyiv. This is where Ukraine’s critical modification comes into play. Ukrainian resistance in Sumy oblast, particularly in late March, used small, mobile light infantry forces to disrupt Russian logistics elements, which were vital both to support the movement toward Kyiv and to sustain deliberate fire and maneuver efforts to encircle and reduce the strongpoints. These light infantry forces were equipped with strong and extensive antiarmor capabilities and worked in the gaps between the deliberate defensive strongpoints, conducting raids on Russian lines of communication and hit-and-run spoiling attacks on concentrating forces and convoys. These teams managed to limit Russian operational reach by interrupting their tempo and demoralizing Russian forces, particularly sustainment forces. The Ukrainian resistance, largely local Territorial Defense Forces, with advanced antitank guided munitions provided by the West, contributed to an ideal economy-of-force concept built on overlapping and mutually supporting strongpoints.

The days between March 21 and March 24 represented a particularly high-intensity period of Ukraine’s hedgehog defense and the activity of its mobile light infantry. The combination of determined resistance denying the Russians control over cities and key terrain that Ukrainian forces defended as strongpoints and the roving light forces disrupting the Russian attempts to mass combat power and support any encircling forces was decisive in the fight for Sumy. On March 29 the Sumy axis saw a significant reduction in Russian offensive efforts due to the successful Ukrainian tactical disruption, leading to a lessening of Russian pressure on the key strongpoints. Russia’s inability to exploit the gaps in the Ukrainian noncontiguous defensive front seems to be largely because of the efforts of the mobile, light infantry forces. The overall effect of this—as well as the defense of Chernihiv, Kharkiv, and other areas east of Kyiv—was the dis-integration of the Russian offensive operational effort in the first week of April and the abandonment of the Kyiv axis and a complete withdrawal from northeast Ukraine.

Lessons for the US Army

In a 2014 paper, retired Lieutenant Colonel Raymond Millen made a persuasive case for a modern, adapted take on the elastic defense-in-depth concept, which he called “resilient defense.” The key principles of Germany’s World War II elastic defense concept—“dispersal and depth,” “establishment of the ‘vacant battlefield,’” and “tactical agility”—remain applicable today, Millen argued. His resilient defense concept is formed of multiple layers: an outpost sector to deny enemy reconnaissance and break up enemy cohesion, and a main line of resistance (first and second echelon) to attrit enemy forces, thereby facilitating a deliberate counterattack. Key to this approach are terrain anchor points, reinforced antitank strongpoints to counter enemy armor. All of this sounds familiar and would comfortably fit within current US Army doctrine for the defense, particularly in area defense and the concept of a security area, a main battle area, and a forward edge of the battle area.

Where the Ukrainian adaptation to the hedgehog defense contrasts with US Army defense doctrine is in the use of mobile, mounted, light infantry as opposed to mechanized or motorized infantry. “Dismounted infantry forces facing an armored enemy force,” US Army doctrine states, “are primarily used in static roles.” There involves significant risk for the US Army’s infantry brigade combat teams, however, especially when the war in Ukraine has shown the decisive impact mobile light infantry can have against motorized and armored formations in a properly conducted hedgehog defense.

How do we get US Army light infantry proficient in this type of modified defense? Flexibility, coordination, and synchronization between defensive strongpoints and mobile light infantry are required. Simple and reliable communication is a critical capability to support dispersal and concentration, allowing the roving bands of marauding light infantry to act in a similar manner to German U-boat operations during the Battle of the Atlantic. As land-based wolfpacks, communications enable the dispersal of forces to support survivability and counterreconnaissance while also ensuring the ability to concentrate to exploit identified opportunities before dispersing once again.

The current composition of armored brigade combat teams and even Stryker brigades lacks the number of infantry dismounts needed to organically conduct the deliberate and sustained roving aspect of the hedgehog defense to the degree effectively demonstrated in Ukraine. The demands placed on their infantry for platform operation and support, and signatures from these vehicles, preclude them from achieving the mobility and survivability that small, hunter-killer, light infantry teams need to operate between strongpoints. Even Stryker infantry units still emit a large signature limiting their mobility and survivability in the face of an enemy combined arms attack. Such units are better employed in direct support to the strongpoints, while light infantry roam between them or concentrate temporarily as a counterattack or exploitation force. A study to validate the current force structure of US armored formations for methods to increase infantry dismounts in US armored and Stryker formations could yield important insights, and it might also prove effective to return to a cross-organization method of mixing light infantry with Stryker infantry and armor. Optimizing light infantry for this purpose is key. To that end, equipping strictly light infantry forces with platforms like the Infantry Squad Vehicle to enhance mobility holds promise, but even this raises questions. How much is too much, how big is too big, and where should the mobility requirement lie? These are all important discussions. However, the most important factor for this analysis is that light infantry need mobility to conduct this sort of defense.

Light infantry formations should train using the adapted hedgehog defense at the Army’s combat training centers, focusing on light, mobile infantry force activities outside of the deliberate defensive positions. This will also likely require a shift in the balance during each training rotation between light and heavy formations. Additionally, the opposing forces at the combat training centers should continue to learn and refine lessons on the application of small, light infantry forces against an attacking armored force to train armored brigade combat teams and Stryker brigade combat teams against this type of flexible defense, while the rotational units should also be led to practice employing mobile infantry formations in the defense.

Mobility, survivability, and lethality are foundations to successful close combat actions and cannot be taken for granted on the future battlefield. Likewise, fighting in the defense on a linear front against an enemy force cannot be assumed in a sustained, high-intensity, large-scale combat operation. This is a gap in current doctrine. The US Army may find itself in a particular portion of a theater or line facing an opponent who has mass, fires, and combined arms superiority—a situation Germany confronted on the Eastern Front and Ukraine did in Sumy. In a major conventional war, somewhere, even if only on a secondary front for the US Army, an infantry brigade combat team may find itself overextended, unable to effectively practice elastic defense and facing a locally superior opponent. In that event, those infantry forces will need to be proficient in adopting the practice of the hedgehog defense so effectively illustrated by Ukraine in the defense of Sumy.

Michael G. Anderson is a US Army infantry officer with four overseas deployments and a 2022 graduate of the School of Advanced Military Studies. He has published over a dozen articles, including in the Journal of Strategic Security, the Journal of Military and Strategic Studies, and Military Review, and is the author of Mustering for War (Army University Press).

The views expressed are those of the author and do not reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

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