THE NEXT TEST FOR MODULARITY: DEFENSE-IN-DEPTH IN EUROPE

Unlike a permanent forward-basing solution with forces across the entire border, defense-in-depth strategies rely on smaller formations that could abandon perimeter fortifications and augment strongpoints to defend against an incursion.

Multiple competing priorities will challenge land forces in the European theater over the next ten years. Russia’s continued aggression after the culmination of current hostilities, in combination with an increasingly hostile China, poses material and readiness dilemmas for the U.S. Army. Strategic opportunities exist, however, to parry these likely challenges by harnessing lessons learned from both V Corps and U.S. Army Europe and Africa (USAREUR-AF) during crises and competition after the Russian invasion in February 2022. By calibrating modular, rotational force posture; increasing permanent European presence; investing in a robust exercise regime; and emphasizing persistent engagements at the theater level and below, the United States can enable combat-credible postures to deter hostile actors in an increasingly resource-constrained environment.

Historical Analogy: The Roman Frontier

Understanding a past example of the strategic thinking behind the current American distribution of forces in Europe is helpful. The U.S. tactical force posture and “defense-in-depth” mirrors the Roman frontier defense of the third century CE. As described by Luttwak in his book Grand Strategy of the Roman Empire, a defense-in-depth strategy is “based on a combination of static frontier forces and mobile field armies” (132). Unlike a permanent forward-basing solution with forces across the entire border, defense-in-depth strategies rely on smaller formations that could abandon perimeter fortifications and augment strongpoints to defend against an incursion. Luttwak refers to the mobile, defensive force as an “elastic defense” and the static strongholds as the central component of defense-in-depth (130). U.S. forces rotationally occupy similar “strongpoints” across Eastern Europe. However, the Roman defense-in-depth came to rely on what Luttwak described as “part-time peasant-soldiers (limitanei) who farmed their own assigned lands and provided a purely local and static defense (171).” These limitanei defended gaps in the frontier due to a lack of mobilized, professional forces, and they would prove to be a liability. Like the Roman Empire, the United States is experiencing a strain on its professional force that will require augmentation from allies and partners as well as other American components to sustain a protracted defense.

Calibrated Rotational Force Posture

Improving the command and control of rotational forces at the division level is the first step toward strengthening NATO’s eastern flank. Between the Russian invasion of Crimea in 2014 and the start of the war in Ukraine in February 2022, the USAREUR-AF managed the rotational presence of one division mission command element (MCE). This division, manned by approximately two hundred personnel, managed one brigade combat team (BCT) and a combat aviation brigade as the minimum combat power to deter Russian aggression. This posture notably failed to deter Russian aggression against Ukraine. After the Russian incursion, the United States increased the rotational forward posture to two division MCEs. These divisions, the 4^th Infantry Division and the 101^st Air Assault Division, commanded three BCTs and sufficient enabling units to sustain the overall increase in forces while simultaneously maintaining command requirements at their respective home stations: Fort Carson and Fort Campbell.

Increasing complexities in the European theater and burgeoning global responsibilities are pressuring division MCEs at the tactical level. Furthermore, personnel shortages are making “split-based” mission command more challenging to sustain due to legal restrictions on soldier “deployment” versus “dwell” ratios. The operational tempo of a “peacetime” Army, for example, is beginning to rival solider “time-away” during the two wars in both Afghanistan and Iraq. The Army must create enduring expertise at the division level, which rotational command structures cannot achieve. In the unlikely event of large-scale combat operations, the United States must recognize it will fight with modular, rotationally deployed divisions. The fully-resourced division as the ideal unit of action for the Army of 2030 will not be the blunt fighting force. To mitigate this risk, increasing division rotations to twelve months from the current six- to nine-month rotations will reduce lost expertise, permit greater unit understanding of the situation, and improve overall force posture. Furthermore, identifying a single division—potentially the First Armored Division from Fort Bliss—as the European-aligned division under V Corps will enable commanders and staffs at echelons below brigade to fully embrace the European mission and improve efficiencies. Providing divisions ownership over the long term will help the corps and theater army with enabler calibration to optimize the use of combat power.

Increase in Permanent European Presence

Increasing the American permanent presence in Europe is the second mechanism to build sustained operational and tactical advantages. Since V Corps cased its colors in 2013, U.S. permanent stationing in Europe has steadily diminished. By the start of the war in Ukraine in February 2022, V Corps was stationed at Fort Knox, KY, although the corps did have a forward command post in Poznan, Poland. Meanwhile, the only brigade combat organizations permanently stationed in Europe were the 2nd Cavalry Regiment, 41st Fires Brigade, and 12th Combat Aviation Brigade.

The Army and USAREUR-AF must increase permanent basing, at a minimum for command-and-control elements, in Poland and Germany. To its credit, USAREUR-AF and V Corps permanently assigned the first unaccompanied soldiers to Victory Corps Forward at Camp Kosciuszko (“Camp K”) in Poznan, Poland beginning this year. Increasing permanent forward presence at the tactical level in Germany and Poland builds the required expertise for the European problem set that mitigates risk incurred during unit rotations and attracts talent from within the Army toward stable opportunities in the European theater of operations.

Exercises are the mechanisms to gain competitive advantages in crisis, potentially setting conditions that change adversarial calculations concerning the benefits of continued escalation.

Robust Exercises

Named, preplanned, and announced exercises are another tenet of competition that provides commanders operational flexibility in a crisis. Exercises are the mechanisms to gain competitive advantages in crisis, potentially setting conditions that change adversarial calculations concerning the benefits of continued escalation. Exercises enhance a competitive edge in three ways: communicating capability and resolve to adversaries and fence-sitters; increasing readiness and interoperability within alliances, partnerships, and units; and serving as a mechanism for operational flexibility during a crisis. Preplanned and communicated events allow commanders to respond without risking escalation due to the appearance of pre-coordinated training, as the 2^nd Cavalry Regiment did during the initial crisis after the Russian invasion in February of 2022.

Exercises play a critical role in the U.S. “defense-in-depth” strategy by building partner capacity and increasing U.S. and NATO interoperability. On average, each fiscal year, the United States Army European Command (USEUCOM) hosts approximately thirty exercises that span from the national level (European partner countries) to the functional service components. When looking at the Russian Federation, NATO’s comparative advantages are the scale, complexity, and quantity of its exercise regime. As part of exercise certification and looking to a sustainable, joint command and control element in Europe, the Army must certify V Corps as a Joint Task Force capable of commanding NATO organizations.

Persistent Engagements

Maintaining and synchronizing engagement opportunities with allies and partners at the Corps and Division level is critical to securing combat advantages during competition. General officer engagements with allies and partners enable significant gains at the tactical level. Through well-developed relationships, demonstrated tactical competence, and a reputation as America’s tangible commitment to European security, V Corps’s engagements facilitated infrastructure and basing development, training opportunities, and enabled allied combat power. A coherent and deliberate engagement strategy produces tactical benefits essential to building a cooperative, combat-credible posture that synthesizes U.S. combat power with resident host-nation advantages and enables a multi-domain alliance.

Conclusion

A strategy of rotating mobile forces between strongpoints across Eastern Europe and the Baltics as an economy-of-force alternative to a large, standing presence in Europe is consistent with the Romans’ solution to a comparable strategic situation. As the United States pursues a similar strategy, the U.S. Army would be wise to protect against the dangers presented to the force. The limited supply of mobile forces required the Romans to enlist part-time peasant soldiers, who were not as well-trained or reliable as full-time troops (Luttwak, 171). The American defense-in-depth strategy stresses the professional force and requires coordination between allied and partner forces to satisfy specific capability gaps. The U.S. defense-in-depth in Europe will deter by denial so long as partnerships with professional military forces remain strong. In the end, calibrating modular rotational forward postures, increasing permanent forward presence, maintaining exercise tempo, and adapting a coherent engagement strategy will prove essential to preparing the tactical environment for the upcoming fighting seasons and the longer-term defense of Europe.

Blair Wilcox is a lieutenant colonel and a U.S. Army Strategist (FA59) currently assigned as the Deputy Director in the Strategic Landpower and Futures Group in the Center for Strategic Leadership at the U.S. Army War College. Before his current assignment, he taught in the Department of Social Sciences at the U.S. Military Academy from 2016-2020. His first functional assignment as a Strategist was at V Corps where he was the lead author for the Corps Subordinate Campaign Plan and Operational Approach. Blair helped stand up the Corps, deployed with the Corps during crisis, and served as the Chief of Plans during his final year in the G5.

The views expressed in this article are those of the author and do not necessarily reflect those of the U.S. Army War College, the U.S. Army, or the Department of Defense.

Photo Description: Against a backdrop of a German village, U.S. Army tanks maneuver for a river crossing during, REFORGER ’82, the multi-national military training exercise.

Photo Credit: Photographer unknown, courtesy of the U.S. DoD