The Russian and Ukrainian Spring 2021 War Scare

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This paper is part of the CSIS Understanding the Russian Military Today executive education program.


The massing of troops and hardware by Russia along its border with Ukraine in April 2021 brought back memories of Russia’s incursion into Ukraine in 2014–15 and raised fears of another round of Russian aggression against its neighbor. Although the worst-case scenario did not materialize, these events require close attention and in-depth research because they could happen again should Russia’s leadership assess that their national security interests are at stake once more.

Several observations arise from a detailed analysis of this spring’s war scare between Russia and Ukraine. First, statements on the number of Russian troops involved were misleading in certain respects—the majority of troops in question were already at Ukraine’s borders from past incursions. Second, Russian armed forces involved in these exercises practiced complex scenarios, including encirclement of the Ukrainian Joint Forces Operation in Donbas and blocking of Ukrainian access to the Black Sea. Third, Russian public justifications of the movement of troops and hardware near Ukraine’s border were unpersuasive upon closer look. It seems that a major driver of Russian actions was the desire to send signals to the new U.S. administration—namely that the Biden administration should not attempt to challenge the status quo vis-à-vis Ukraine by bringing it closer to the North Atlantic Treaty Organization (NATO) or aid in the liberation of parts of occupied Donbas. Finally, though Russia might have succeeded in sending specific signals to the Biden administration, the intended effect backfired in the case of Ukraine.


In April 2021, the international community’s attention was focused on the latest round of tensions between Ukraine and Russia. Kyiv and its international partners accused Moscow of unprovoked concentration of troops and equipment along the Ukrainian border. At the same time, Moscow acted as if nothing unusual was taking place and framed it as just another round of Russian armed forces readiness checks after the winter period of training.1

It is not unusual for Russia to use armed forces readiness checks to work out complex scenarios involving masses of troops and equipment. For instance, in April 2019, the Russian Black Sea Fleet and the Fourth Air and Air Defense Forces Army of the Southern Military District practiced different elements of high-intensity warfare in the region against a hypothetical threat from the United States and NATO.

What was unusual was the size and scope of Russian military activities near the Ukrainian border in the spring of 2021. Reports and photo and video materials of movements of Russian armed forces’ hardware and troops toward the Ukrainian border were reminiscent of Russia’s actions in 2014–15. At that time, Russia had stationed forces along the Ukrainian border, some of which took part in fighting in Donbas. Given this experience, this year’s mass movement of hardware and troops made some experts think about the worst-case scenario—an all-out Russian aggression against Ukraine—which would go beyond the more limited use of force in 2014–15.

The spring 2021 war scare raised several interesting questions: First, how many Russian troops were involved? Second, what possible scenarios were the Russian forces preparing for along the Ukrainian border? Third, what grand strategy aims did Russia want to attain with this mass concentration of equipment and troops? And finally, what kind of wider geopolitical implications could this war scare have produced?

What was unusual was the size and scope of Russian military activities near the Ukrainian border in the spring of 2021. Reports and photo and video materials of movements of Russian armed forces’ hardware and troops toward the Ukrainian border were reminiscent of Russia’s actions in 2014–15.

Size of the Russian Deployment

According to Pentagon press secretary John Kirby, the spring deployment of Russian forces near Ukraine’s border was the largest since 2014. It is notable that the U.S. Department of Defense refused to provide precise statistics on the number of Russian troops brought to the Ukrainian border. Still, U.S. European Command raised its watch level from a “possible crisis” to a “potential imminent crisis” at the end of March. It also increased the flight tempo of its intelligence, surveillance, and reconnaissance (ISR) platforms to better understand the situation on the ground. Ukrainian authorities asserted that the number of Russian troops along the mutual border increased to 100,000 to 120,000 by mid-April, which was more or less accepted in the West as an accurate number, according to public statements.

On April 13, Russian minister of defense Sergei Shoigu acknowledged for the first time that the movement of additional troops indeed took place. Specifically, he said that two combined arms armies (CAA) and three formations of airborne forces were moved to the western border as part of readiness checks after the winter period of training. In a subsequent announcement, Minister Shoigu elaborated that the formations in question were the 41st and 58th CAAs, as well as the 7th and 76th air assault divisions and the 98th airborne division.

Even before Moscow initiated movement of equipment and troops to the western border in the spring, there were almost 87,000 Russian troops stationed there already. This was the direct result of Russian decisions made in 2014–16 to create a permanent military infrastructure near the border with Ukraine and in occupied Crimea. As a result, the headquarters of 20th CAA were moved to Voronezh from Nizhniy Novgorod in 2015, and two motor rifles divisions (3rd and 144th) were established under the command of this army in 2016. The 8th CAA was reestablished in Rostov region at the end of 2016 with the 150th Motor Rifle Division and two corps in occupied parts of Donbas under its control. In 2017, Russia formed the 22nd Army Corps in Crimea. According to Ukrainian estimates provided to the Organization for Security and Co-operation in Europe (OSCE) in July 2020, Russia is able to generate 28 battalion tactical groups (BTGs) using formations just on the other side of the border without any additional deployments. Thus, the majority of the forces cited as part of the exercises were already there. Ukrainian estimates provided to the OSCE in June 2021 show that only 12,000 Russian forces were removed from the border, and the rest remain in place. As a result, the number of troops remaining is more or less the number of troops that was at the border before the exercise.

Statements by Minister Shoigu that two additional CAAs and three other formations of airborne troops were moved to the western border should be treated with skepticism. If Russia had in fact assembled no more than 100,000 to 120,000 troops close to the Ukrainian border with almost 87,000 troops already there, it means that only some parts of those additional formations were actually deployed. Otherwise, the total figures would have been much higher, as each Russian CAA now has at most approximately 20,000 to 30,000 troops, and each paratroopers’ division has 6,000 to 6,500 troops. Shoigu’s statement was likely made intentionally as a part of a deliberate campaign to make Russian forces deployed near Ukraine look more formidable, threatening, and persuasive.

Even before Moscow initiated movement of equipment and troops to the western border in the spring, there were almost 87,000 Russian troops stationed there already. This was the direct result of Russian decisions made in 2014–16 to create a permanent military infrastructure near the border with Ukraine and in occupied Crimea.

Russia’s Scenarios

Given how Russian armed forces have used readiness checks after winter training to practice complex scenarios in the past, it is fair to guess that the same situation took place this spring. Indeed, it would have been strange for the Russian General Staff to create such a concentration of forces without working out some scenarios and operational plans. For Russia to be credible in the eyes of target audiences at the strategic level, the Russian armed forces need to be credible at the operational level, which means actively carrying out and improving their scenarios and operational plans.

There are ample reasons to say that Russian armed forces close to Ukrainian frontiers were practicing either a limited strike to block Ukrainian access to the Black Sea or a more ambitious plan to encircle all Ukrainian forces in the east.

First, according to sources that use open-source intelligence (OSINT), such as the Conflict Intelligence Team, and Russian public announcements, additional formations and troops were moved to occupied Crimea (parts of 58th CAA and airborne troops’ divisions) and the 20th CAA’s area (parts of 41st CAA), which is concentrated along the northeastern part of Ukraine. Such a concentration is notable as it has been done at the flanks of the Ukrainian Joint Forces Operation in Donbas, whose main task is to deter Russian-controlled forces in the region. By deploying additional troops in that region, Moscow was hinting at the possibility of encircling the Ukrainian Joint Forces Operation (30,000 to 35,000 troops). While forces under the 8th CAA could control pinned-down Ukrainian forces in the front in Donbas, Russian forces would strike simultaneously from Crimea and the Voronezh region to encircle Ukrainian forces.

Two other factors give credence to this hypothesis. First, when the main operations of the Kavkaz 2020 (Caucasus 2020) strategic command and staff exercise played out at the Kapustin Yar test range last September, the staff of the 58th and 20th CAAs were involved in working out a scenario that stipulated the encirclement of enemy forces through a combined two-flank strike converging in the rear and simultaneous repelling of enemy counterstrikes. This scenario resembles the situation of spring 2021 when Russia reinforced occupied Crimea in the south with parts of the 58th CAA and paratrooper formations as well as the 20th CAA in the northeast along with the 41st CAA.

Second, when Russian senior officers compared Kavkaz 2020 and Kavkaz 2016, they said that during the latter exercise, Russian forces practiced “localization of hypothetical borderland armed conflict in the area of Southern Military District responsibility,” whereas the 2020 iteration focused on the “localization of interstate conflict with foreign forces involved.” The change in focus suggests that the Russian military leadership’s ambitions increased in the last four years as the armed forces have progressed and improved. In Kavkaz 2016, Russian forces practiced the 2014-15 Donbas scenario (i.e., stabilizing a situation with limited force in case of a hypothetical Ukrainian offensive). In 2020, the scale of Russia’s deployment was much larger, which is why the main element of last year’s Kavkaz strategic command and staff exercise was conducted at the Kapustin Yar range. Its dimensions (60 km in width and 120 km in depth) are much bigger than those of the Opuk range (30 km in width and 15 km in depth, where the main episode of Kavkaz 2016 was carried out) and allow for much more complex and ambitious scenario exercises. A hypothetical attempt to encircle the Ukrainian Joint Forces Operation in Donbas falls into this category.

In spring 2021, active movement of forces was also taking place in Crimea. The limited maneuver space is why only parts of the 58th CAA and airborne troops divisions were brought to the peninsula. Signal brigades of both the 58th CAA and airborne troops were present in the peninsula during the course of readiness checks after the winter period of training. This fact is consistent with official statements that forces in occupied Crimea practiced deployment of interservice grouping of forces in an operational direction. The ability of forces to effectively deploy and fight in new places depends on effective communication and cooperation by signal brigades.

It is also notable that the Russian armed forces brought amphibious ships from the Baltic Fleet, Northern Fleet, and Caspian Flotilla to occupied Crimea. Ten thousand troops were involved in the active phase of training under the supervision of both the Russian minister of defense and the chief of general staff at the Opuk range, exercising blocking Ukraine from accessing the sea partially or entirely. Those amphibious ships allowed Russians to practice landing at least two BTGs. Simultaneously, at least 2,000 troops parachuted into the operational depth of defense of a hypothetical enemy, effectively breaking through the enemy’s defensive belt and making vulnerable its rear. These Russian paratroopers are usually used to repel possible counterattacks of the enemy and streamline further offensive movements of friendly forces. In all phases of the exercise, attack helicopters, tactical-operational fighters, and bombers supported the troops. The combined amphibious and paratrooper landings, BTGs moving on land, and firepower support from air would have partially or fully blocked Ukraine’s access to the sea. The command and control (C2) echelon practiced using command, control, communications, and computer ISR (C4ISR) networks and equipment to make quicker and timelier decisions. Russia’s partial or full block of Ukrainian access to the Black Sea would have meant another serious blow for the Ukrainian economy, which depends greatly on Black Sea ports for exporting agricultural products as well as metals and chemicals.

The large scale and complex training in occupied Crimea this spring might also be seen from another perspective. A majority of Russian forces on the peninsula were left out of the Kavkaz 2020 exercise since the main scenario was practiced inland (on the Prudboi and Kapustin Yar ranges). Compared to the Kavkaz 2016 exercise when the main element took place at the Opuk range, the forces and ranges in Crimea were practically not involved. This spring’s complex drill at the Opuk range might be seen as a kind of compensation for last year’s noninvolvement.

Thus, the movement and deployment of troops and equipment in the spring of 2021 provide ample reasons to say that Russians were practicing complex scenarios (full or partial blockage of Ukrainian access to Black Sea) as they did in occupied Crimea and were hinting at the possibility of a more ambitious scenario (encirclement of the Joint Forces Operation contingent in Donbas).

Reasons for Russian Actions

As events progressed, Russia tried different arguments to justify its decision to concentrate the unprecedented number of troops and equipment along its borders with Ukraine, including that:

  • As Minister Shoigu suggested, it was a defensive reaction to the U.S./NATO Defender Europe 2021 exercises;

  • It was a preemptive move to deter a possible Ukrainian offensive in Donbas;

  • The Russians feared Ukrainians, inspired by last year’s Azerbaijani successes in the Nagorno-Karabakh region, would make another attempt to liberate parts of occupied Donbas; and

  • Movements of Ukrainian forces to Donbas were proof that Kyiv was up to something nefarious.

The arguments do not hold up against scrutiny. Ukraine was not involved in NATO’s Defender 2021 exercise, which was conducted largely in the Balkans and on a much smaller scale compared with Russia’s deployment this April. The same is true with the idea that Azerbaijani successes might prompt Ukraine to switch its posture in Donbas from strategic defense to offense. It is true that Ukraine in 2018 and 2020 purchased hardware such as Bayraktar TB2 unmanned combat aerial vehicles (UCAVs), which contributed to Azerbaijani successes in the Nagorno-Karabakh region.

However, the Ukrainian armed forces still lack the critical mass of systems (ISR, C2, electronic warfare, and long-range fires and precision munitions) to conduct modern warfare, which is grounded in the ability to simultaneously fight at a front line and prevent enemies from bringing reinforcements from the rear. Without the critical mass of technologies for modern deep operations, it would be imprudent for Ukraine to switch from a strategic defensive posture in Donbas to an offensive posture.  Periodic rotational movements of Ukrainian forces to and from the frontlines are not unusual as they have been carried out continuously since 2014.

What informed Moscow’s decision to move additional troops this spring? Two reasons seem more plausible than others. First, on January 20, 2021, Joe Biden assumed the U.S. presidency. During the presidential campaign, Biden was the most outspoken candidate regarding Ukraine; as the presidential hopeful, he promised to make Ukraine one of the main elements of his foreign policy and signaled a willingness to increase defensive weapons assistance. Since entering the White House, Biden and his team have made a number of statements that demonstrated support for Ukrainian authorities. Given such statements, it is likely that the Russian government decided to act preemptively and ensure the status quo in Russia’s frontiers. Russia has escalation dominance, and U.S. and Ukrainian attempts to change the status quo established after 2014–15 events would be costly. Russia made clear through its limited military interventions in Donbas that it would not allow Ukraine to fully restore order and sovereignty in the region.

Another likely reason was to forestall Ukrainian membership in NATO. Statements from Ukrainian officials, including the head of Ukrainian Ministry of Defense, expressed interest in participating in the NATO Membership Action Plan in 2021. It is widely known that Euro-Atlantic integration of Ukraine is a nonstarter for Russia. As a result, Moscow decided to act preemptively and to vividly demonstrate to NATO members the risks associated with possible Ukrainian integration with NATO. As Vladimir Putin made clear in his latest article on the Russian and Ukrainian nations, Moscow would do everything in its power to prevent countries of the former Soviet Union from becoming the staging area for anti-Russian activities of external powers, which first and foremost means the United States and NATO.


It seems that Russia was relatively successful in driving the message home to one of its target audiences. President Biden and his team adopted the idea of “stable and predictable” relations with Russia, which in practice means U.S. refusal to take steps that could radically alter the current status quo and cross Russia’s red lines. Thus, during the June 2021 NATO Brussels summit, allies formally reiterated the 2008 Bucharest summit decision that Ukraine will one day be a NATO member. But on the flip side, U.S. government public announcements made clear that Washington was not in favor of bringing Ukraine into NATO in the near term.

It is even more telling that during the spring war scare, the Biden administration considered the option of providing Ukraine with an extraordinary package of defensive military assistance for $100 million but in the end, decided not to proceed with it. Such hesitancy could also be seen as acceptance of the idea that it is useless to challenge Russia in its periphery where it has the preponderance of forces and power.

On the other hand, Russia is the only one to blame for Ukraine wanting to join NATO. The more Moscow threatens Ukraine with permanent military infrastructure or movement of additional troops and equipment, the more Ukraine wants to join NATO, as the latter sees how quickly the security environment can deteriorate without the concrete security guarantees that NATO provides.

It is striking how during this war scare, Ukrainian president Volodymyr Zelenskiy switched his attitude toward NATO integration. His public pronouncements went from some ambiguity during the 2019 presidential campaign to full support this past spring. In this, history has repeated itself. Back in the 2014 presidential elections, Petro Poroshenko was also not a strong supporter of NATO integration, thinking that such an approach might bring peace in Donbas. It did not help, and active use of Russian forces in Donbas left Ukraine with no alternative than to try to join NATO. The same is true today. Russian threats and aggressive moves might influence the target audience in the West in the way Moscow desires, but it will have the opposite effect with regard to Ukraine. Another Ukrainian leader now unambiguously wants his country to join NATO. 

Mykola Bielieskov is a research fellow with the National Institute for Strategic Studies under the President of Ukraine. Formerly he worked for the Ukrainian Institute of World Policy.

Views in the text are author’s only and do not represent the official position of the National Institute for Strategic Studies and the Office of the President of Ukraine.

This publication was funded by the Russia Strategic Initiative, U.S. European Command in Stuttgart, Germany. Opinions, arguments, viewpoints, and conclusions expressed in this work do not represent those of RSI, U.S. EUCOM, the Department of Defense, or the U.S. government.

This report is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

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Mykola Bielieskov

Research Fellow, the National Institute for Strategic Studies