Download the complete publication here: No. 25-897, Understanding Irregular Warfare (Jul 25) [PDF - 5.1 MB]

Additional contributing authors: LTC Jahara Matisek, MAJ (RET) James Micciche, LCDR Adam Christensen

Acknowledgement

This publication would be inaccurate and incomplete, without the collaboration from the Irregular Warfare Center, The Irregular Warfare Initiative, the U.S. Army Irregular Warfare Proponent, and the U.S. Army Combined Arms Doctrine Directorate. It would also be incomplete without the perspectives from other services, such as the U.S. Marine Corp Ground Combat Element Division and Service-specific academic institutions such as the Naval War College and the Air University. We are grateful for an ally institutional perspective from the Netherlands Defence Academy.

U.S. Irregular Approach to Joint Campaigning

Chapter 1: Introduction

Background

The Department of Defense (DOD) recognizes two general forms of warfare: conventional and irregular. DOD defines conventional warfare as a violent struggle between nation-states or coalitions, and alliances of nation-states, fought with conventional forces.” It is important to note that as we seek to rebuild our own lethality in conventional warfare, our adversaries will become more likely to emphasize irregular approaches in their competitive strategies to negate our advantages and exploit our disadvantages.

As the joint force increases its conventional credibility, Army forces can expect threats to increasingly pursue irregular warfare (IW). The armed conflicts in both Afghanistan and Iraq combined irregular and conventional warfare because the U.S. and its coalition ultimately sought to defeat enemy conventional forces, terrorists, and insurgencies. While they were fighting, Army forces addressed grievances within the local populace and countered external threats, such as China, Russia, and Iran. Yet, despite the pivot to great power competition, the U.S. Army recently invested into security force assistance brigades (SFABs) which, while being a conventional force, frees up other conventional forces to focus on conventional warfare, and has an enduring mission that achieves desired strategic outcomes. This assures allies through building partner capacity which simultaneously deters adversarial aggression.

The SFABs demonstrate that both IW and conventional warfare should not be thought of as dichotomous forms of warfare, each with its own distinct capabilities, nor as hybrid warfare (as all warfare is hybrid), but rather as complimentary means to strategic ends. IW is often conducted independently of conventional warfare. IW provides options to economize the use of combat power and relies on nonmilitary sources of power to achieve policy aims. The U.S. irregular approach includes irregular activities during competition below armed conflict to create and exploit strategic advantages to win without fighting. During armed conflict irregular warfare adds lethal force to compel enemies, but at levels that prevent escalation and help avoid the high risk of conventional warfare. The Army’s irregular approach to joint campaigns may require influencing populations but may also focus on eroding enemy capacity and its political will to pursue malign interests.

This recognition is part of a wider discussion in which the term IW is imperfect because strategic competition is neither irregular, nor is this form of competition really warfare, because some believe that violence is not a defining feature of IW. Yet, because warfare, which is considered how one wages war, is the second part of the name in IW, some believe that IW must be binned under the context of armed conflict. Some proponents of this view acknowledge the importance of nonlethal actions and call them irregular activities. Military forces conduct irregular activities below the threshold of armed conflict and then weave them in with IW and conventional warfare when policy requires armed conflict. There is also the discussion that, as an alternative way forward, we should be thinking of IW in terms of irregular competition, in which the U.S. military must, “Acknowledge competition’s two coequal parts: the threat of military domination through conventional deterrence and the contest for legitimacy and influence through irregular competition.” However IW is conceptualized, consider that not having a universally accepted definition for modern warfare or contemporary conflict will lead to further misunderstanding of how to apply nuanced approaches to adversarial capabilities or, far worse, not understanding it all and thus affording it no space in policy, plans, or strategy. If defined too broadly, then IW has little practical use for policymakers. Define IW too narrowly, then policymakers will fail to appreciate the significance of irregular tactics and strategies.

Purpose and Approach

The purpose of this publication is to inform potential practitioners on IW and to provide recent vignettes and updated definitions. This handbook describes the current IW operations and activities conducted by the U.S. and its allies and partners against threats. Moreover, this handbook is designed to help readers understand a variety of approaches to IW. Finally, this publication supplements formal and informal education conducted at joint service (JS) academic institutions in accordance with the JS J7 IW Curriculum Development Guide.

This handbook is composed of 3 parts, covering 12 chapters, with 9 written perspectives from practitioners and theorists, and 3 appendices. This chapter is the introduction and provides the research design of this handbook as well as an in-depth examination of the definition of IW and its relationship with strategic competition and the strategic environment. Chapter 2 Briefly describes the strategy, policy, and doctrine associated with IW. Chapter 3 describes the U.S. approach to IW through the 12 IW operations and activities and provides vignettes for each. Part 2 describes the 9 informed perspectives on IW ranging across the JS, its academic institutions, civilian universities, as well as perspectives from our Dutch ally. Finally, regarding the appendices to this handbook, while Appendix A is a brief discussion on how China, Russia, and Iran perceive IW, Appendix B is a recommended reading list on IW and, although not all inclusive, is useful for those who wish to read or learn more on IW. The glossary follows as Appendix C.

Definitions Matter

Defining IW is not without its challenges as the services will have their own interpretation of the joint definition. Yet, employing IW during strategic competition requires an understanding in systems thinking or how states leverage their resources against adversaries or enemies to maximize national objectives, while minimizing risk against military escalation through adversarial response. Therefore, to overcome this challenge, IW is defined more comprehensively here.

Irregular warfare. DOD defines IW as a form of warfare where state and non-state actors campaign to assure or coerce states or other groups through indirect, non-attributable, or asymmetric activities, either as the primary approach or in concert with conventional warfare. The term irregular highlights the character of this form of warfare, which seeks to create dilemmas and increase risk and costs to adversaries to achieve a position of advantage. While IW operations and activities assure, they also coerce through both forms of deterrence and compellence (coercion), which are recognized strategic uses of military force across the competition continuum.

The U.S. Army defines IW as, “the overt, clandestine, and covert employment of military and nonmilitary capabilities by state and non-state actors to achieve policy objectives other than military domination against an enemy, either as the primary approach or in concert with conventional warfare.” IW may include the use of indirect military activities to enable partners, proxies, or surrogates to achieve shared or complementary objectives. The main objective of IW varies with the political context, and it can be successful without being combined with conventional warfare.

IW may employ the threat or use of organized armed violence for purposes other than physical domination over an adversary. States and non-state actors may conduct IW when they cannot achieve their strategic objectives by nonmilitary activities or conventional warfare. IW favors indirect and asymmetric warfare approaches, though it may employ the full range of military and other capabilities to erode adversarial power, influence, and will. At its core, the U.S. irregular approach provides, across the competition continuum, economy of force options to joint force commanders (JFCs) that they can tailor to a wide range of policy objectives. Although any operation can have negative outcomes, irregular approach options are less costly and typically incur risk to a smaller number of forces. Irregular approach options provide flexibility and allow JFCs to adjust the level of lethality over time as needed. At the national strategic level, an irregular approach allows policy makers to manage the rate of escalation or de-escalation. In contrast, conventional warfare often leads to rapid and uncontrolled escalation, especially during large scale combat operations.

U.S. Army Irregular Approach to Campaigning

The U.S. Army is currently working on doctrine and training material to mature and unify its irregular approach to joint campaigns. These documents will complement Field Manual (FM)3-Operations, 21 March 2025 and joint doctrine and capture IW lessons learned from history, including recent conflicts in Ukraine and Gaza. The Army’s irregular approach will define key terms, account for different perspectives, and describe how Army forces weave together irregular activities during competition, irregular warfare, and conventional warfare as part of joint campaigns. The Army’s irregular approach uses combined arms thinking for how to employ special operations forces and conventional forces (from all services) together with multinational forces. It also explains how Army forces integrate with other U.S. departments and agencies, multination government agencies, and the wide range of nongovernmental organizations, irregular forces, and the private sector. Integrating with each of these groups requires different considerations for how to generate the unity of effort necessary for success.

The Army’s irregular approach will focus on offensive options, such as unconventional warfare and conducting all irregular warfare activities with an offensive mindset. The Army’s view of IW will not be constrained to population-centric operations that often require long costly U.S. efforts. While retaining population-centric IW as an option, Army doctrine will describe risk and provide enemy-focused options that seek to erode enemy capabilities and capacity for hostile action.

Conclusion

IW is more common than conventional warfare and needs greater emphasis in doctrine. China and Russia pursue their own version of IW against our national interests both at home and abroad, such as the cyberattack on the Colonial Pipeline in 2021, or more recently, Iran-sponsored Houthi forces harassing U.S. Navy ships in the Red Sea. Understanding IW allows for commanders and their staff to plan, prepare, execute, and assess their assigned missions with greater clarity of the threats and capabilities of their adversaries or enemies. Historically, most Army forces employed to conduct IW have been conventional forces. This publication underscores these points.