Table of Contents Introduction The Offense-Defense Balance How Are Russia’s Defenses Organized? What Obstacles Could a Ukrainian Offensive Face? Lessons for Ukraine: Shifting the Advantage to the Offense Next Steps:
Chapter Two How Are Russia’s Defenses Organized? To shift the offense-defense balance in its favor, Russia has designed one of the largest defensive systems in Europe since World War II. It has constructed a line of fortifications roughly 2,000 kilometers long, running from Russia’s border with Belarus to the Dnipro Delta.[12] Approximately 1,000 kilometers of these defenses are located in Ukraine itself, where essentially all conventional warfare between Russia and Ukraine has taken place. Russia’s fieldworks include four semi-independent defensive systems, each of which roughly corresponds to a Ukrainian oblast.
The area that has been most extensively fortified since the 2022 invasion is Zaporizhzhia Oblast, followed by Kherson, Donetsk, and Luhansk oblasts, as highlighted in Figure 1.[13] Although the defensive systems in each oblast are generally built from the same components—ditches, dragon’s teeth, trenches, and artillery positions—each has unique characteristics that represent particular challenges to a Ukrainian offensive.
Overall, Russian defenses are designed to slow a Ukrainian offensive and to channel it into areas advantageous to Russian forces. The Russian fortifications visible in satellite imagery confront Ukrainian military planners with difficult trade-offs. The first dilemma is whether to commit forces against the densely defended approaches to Crimea, the urban areas that dominate Donetsk Oblast, or the more sparsely fortified but less strategically important areas in Luhansk. A Ukrainian offensive against the oblasts bordering Crimea carries further hard choices, forcing commanders to fight through layers of defensive positions more than 10 kilometers deep in Zaporizhzhia or to cross the Dnipro River, a difficult operation that carries the subsequent challenge of defending a beachhead from a counterattack. No matter what their commanders choose, Ukrainian forces will also be subject to repeated counterattacks from multiple directions seeking to isolate combat units from the support they need to sustain the offensive.
Zaporizhzhia: A System of Systems The Zaporizhzhia defensive system consists of roughly three subsystems, as illustrated in Figure 2. The first is an approximately 150-kilometer frontline system that stretches from the town of Vasylivka on the southeastern edge of the Kakhovka Reservoir to the town of Novopetrykivka on the Zaporizhzhia-Donetsk border. This system consists of multiple layers of counter-mobility barriers and infantry trenches in the frontline area supported by prepared artillery positions less than 30 kilometers to the rear, just ahead of the second subsystem of prepared defenses. This longer line also contains another set of defenses around the town of Vasylivka, making the westernmost edge of the line particularly densely fortified.
The second subsystem stretches more than 130 kilometers from the town of Orlyanske to just north of Bilmak. Its makeup differs little from the frontline system, and it could serve Russia well were it to establish a new front line following a successful Ukrainian offensive. The withdrawal of Russian forces to this second line of defenses could also serve as a prelude to Russian counterattacks against the flanks of the Ukrainian advance.
The third subsystem is a constellation of disconnected fortifications surrounding larger towns close to the front line, most of which occupy commanding positions on major railways or roads, and smaller fieldworks along important roadways. None of these fortifications would be sufficient to rapidly establish a new front line in the case of a Russian collapse, but they could slow a Ukrainian breakthrough, enable Russian counterattacks, and prevent the total collapse of the Russian front.
The distance between these subsystems varies, but the territory between them should not be seen as undefended space. Russian doctrine emphasizes both positional and mobile defenses.[14] Russia would likely seek to engage Ukrainian vehicles in these areas using a combination of indirect fire—potentially including airstrikes—and its own fighting vehicles. A Ukrainian breakthrough would likely trigger a rush of Russian armored reserves to the area, where they would seek to engage Ukrainian forces in open terrain while the second and third subsystems underwent final preparations for combat.
The cumulative effect of these systems would be to array Russia’s strongest resistance against Ukrainian efforts to break through to Melitopol or Berdiansk cities. These preparations reflect the high military and political value Russia attaches to control of Zaporizhzhia Oblast. A Russian collapse like the one seen in Kharkiv in 2022 that allowed Ukraine to approach or liberate these cities would pose a serious threat to Russia’s operations in Ukraine. A Ukrainian push through the second defensive line would allow Ukraine to hold Russia’s supply lines in the country at risk, effectively splitting its military effort between two theaters. It would also threaten to reverse the forcible creation of a land bridge to occupied Crimea. Such a breakthrough approaches a worst-case scenario for Russia and therefore incentivizes the construction of a defensive system of the depth and density seen in Zaporizhzhia.
Kherson: Behind a Wall of Water Kherson’s defensive system is also arrayed around defending approaches to Crimea, but it is less dependent on multiple layers of fortifications because of the oblast’s terrain, which favors the defender. Russia has constructed a set of defenses along the Dnipro Delta across from the city of Kherson and at wide intervals along the Dnipro River. These spans of water are wide enough that they would require amphibious assaults, one of the most complex and demanding operations a military can attempt.
Any such assault would be contested by Russian forces in that first line of defenses, and even the most successful crossings of the river would not lead to a dramatic exploitation of Russian rear areas. The logistics involved in supporting such an exploitation across a large body of water are far more complicated than those involved in a ground offensive without such an obstacle. Russia has also constructed a large number of fieldworks to make such an advance even more difficult. Trenches stud the roads in Kherson every few kilometers, which would slow any effort to reach major logistics hubs and trigger the collapse of the Kherson front.
On June 6, 2023, a major dam and power station on the Dnipro River in southern Ukraine were destroyed, causing a significant outflow of water. The flooding prompted evacuations in areas downriver from the Kakhovka dam, including in some parts of the city of Kherson.
Donetsk: Fighting Block by Block The Donetsk front is characterized by a combination of new and old defensive fortifications and complex urban terrain. These factors coupled with the front line’s proximity to Russia itself make a Ukrainian breakthrough in the region unlikely to result in significant exploitation.
Russian units in Donetsk may be able to benefit from defensive positions dug before the 2022 invasion, unlike their counterparts in other parts of Ukraine. The oblast was the site of combat between Ukraine and Russian proxies for almost eight years before the 2022 invasion. As visible in Figure 4, pre-2022 fortifications outnumber post-2022 fortifications approximately three-to-one.
The benefits of these fortifications to Russian fighters will likely be uneven. The quality and readiness of these fortifications are extremely difficult to assess.[16] Some have likely been in disuse so long that they will not give Russian soldiers the full benefits of a recently prepared defensive position, and some are Ukrainian defensive positions that are oriented to defend against an attack moving away from Russia rather than toward it.
The defensive system in Donetsk incorporates two layers of defenses around the town of Olhynka, where several roads meet, but otherwise appears to rely more on the three cities of Donetsk, Makiivka, and Horlivka, as illustrated in Figure 5. A Ukrainian attempt to push through either of these cities is extremely unlikely for an excellent reason: if Ukraine attempted to assault these cities directly, its offensive would become bogged down in urban combat.
Bakhmut has recently become emblematic of the difficulty of fighting in built-up areas, but any combat in these cities would be on another order of magnitude. Horlivka, the smallest of the three frontline cities, had a pre-invasion population of about 240,000 and has an area of more than 400 square kilometers. In comparison, Bakhmut had a pre-war population of about 70,000 and an area of about 40 square kilometers. Any attempt to overrun either of these cities would make the battle of Bakhmut seem like a skirmish in comparison.
Ukraine could conceivably try to bypass either of the cities, but Russia has constructed fortifications between them. Where the cities are closest together, a single line of fieldworks may be sufficient, as a successful Ukrainian breakthrough passing close to either city would find its supply lines exposed to counterattack from city-based Russian forces. In areas further afield, Russia has constructed multiple layers of defenses somewhat comparable to those in Zaporizhzhia, but much closer together—about 5 kilometers in Donetsk compared with 30 kilometers in Zaporizhzhia. This is unlikely to spell failure for Russia. The centrality of the cities and the proximity of the front line to Russia mean that Russian reserves will be able to move into position in Donetsk far more quickly than in Zaporizhzhia and that Ukrainian logistics will face a greater threat in the event of a breakthrough.
Luhansk: Forests and Front Lines The construction of Luhansk’s defensive system is less clear from satellite imagery than those of the other three oblasts. It appears to be broken into a southern and a northern system, with the southern system arrayed primarily around the city of Severodonetsk, and the northern system consisting of a long line of defenses reaching toward the northern border with Russia, as highlighted in Figure 6. The southern system looks a great deal like the defenses around Donetsk Oblast’s three cities and includes the front line in Bakhmut and the forests around Kreminna, where heavy fighting has been ongoing for months with few territorial gains for either side.
The areas north of Kreminna look different. Russian fortifications north of the forest appear in satellite imagery as a defensive line running from Kreminna to the Russian border, split into forward and rear subsystems (as in Zaporizhzhia) in the northernmost parts of the oblast. Many of the fortifications visible in satellite imagery may actually represent a secondary system rather than an intended front line. These fortifications lie just a few kilometers behind a string of towns that hug the eastern bank of the Krasna River. The houses in these towns would provide ready-made fortifications from which the Russians could fight, while Ukraine would be slowed by the need to conduct bridging operations. As a result, Russia might place their first echelon of defenders in these towns, using the fortifications visible in satellite imagery to contain any Ukrainian units that break through beyond the towns.
North of Preobrazhenne, where the river passes to the east of the towns, Russia once again has constructed two major lines of field fortifications, although they appear less complete than other defensive lines. For example, there is an apparent gap between the towns of Pershotravneve, Mykolaivka, and Arapivka: a potential opening less than 30 kilometers by road from Kupiansk, a city in which Ukraine could conceivably mass forces. As is the case in Zaporizhzhia, areas without fieldworks are not necessarily undefended. Russia would still seek to conduct mobile warfare in these areas north of Preobrazhenne, which have already seen tank battles in the past year. A Ukrainian offensive this far north would also create novel vulnerabilities, extending Ukraine’s flank along the Russian border, where political constraints give Russia a degree of safe haven from which to conduct a counteroffensive or strike Ukrainian forces, logistics, and civilians with standoff weapons. Chapter Three published 8/11/2023 https://www.csis.org/analysis/ukraines-offensive-operations-shifting-offense-defense-balance
