Training, advising, and assisting South Vietnamese partners was a key component of U.S. efforts to defeat the Communist insurgency in Vietnam, in accordance with contemporary Army doctrine on counter-irregular warfare.

From “irregular warfare” to
Irregular Warfare

History of a Term

By Jared M. Tracy, PHD

From Veritas, Vol. 19, No. 1, 2023

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The term Irregular Warfare (IW) is pervasive in the modern Department of Defense (DoD) lexicon, but it has a lengthy history. In Cold War-era military publications, IW was not defined but its meaning was generally fixed. After 9/11, it gained popularity and formal definitions, but its meaning became more ambiguous, largely because of its connection to other concepts, especially in the special operations forces (SOF) arena.1 This was evident when the U.S. shifted from Counter-Violent Extremist Operations (C-VEO) to Great Power Competition (GPC) in recent years. This brief history of the term IW begins during the Korean War (1950-1953).

Army FM 31-20 (1951) linked irregular warfare with guerrilla warfare, namely Communist insurgencies.
Army FM 31-20 (1951) linked irregular warfare with guerrilla warfare, namely Communist insurgencies.

In February 1951, the Army published Field Manual (FM) 31-20: Operations Against Guerrilla Forces. It relayed that the “term ‘guerilla warfare’ is used loosely to describe all kinds of irregular warfare.”2 Though undefined, IW was synonymous with guerrilla warfare. FM 31-21: Organization and Conduct of Guerilla Warfare (October 1951) defined guerrillas as an “irregular force, organized on a military basis, supported chiefly by sympathetic elements of the population, and operating against established … authority.”3 IW was linked primarily to Communist-inspired insurgencies, with connotations of being a duplicitous form of warfare.

Captain Joseph Ulatoski, commander Task Force KIRKLAND, a U.S.-led anti-Communist partisan unit headquartered off the Korean east coast, addresses a formation of recent airborne graduates on the island of Nan-do, 1952.
Captain Joseph Ulatoski (far left), commander Task Force KIRKLAND, a U.S.-led anti-Communist partisan unit headquartered off the Korean east coast, addresses a formation of recent airborne graduates on the island of Nan-do, 1952.

In the 1960s, terms such as Unconventional Warfare (UW), Counterinsurgency (COIN), and Special Warfare gained traction. Though seldom used by comparison, IW remained tied to Communist revolutionary doctrine. The U.S. Army Special Warfare Center’s “Readings in Counter-Guerrilla Operations” (1961) described IW as central to Mao Zedong’s philosophy.4 In 1961, the Army published FM 31-15: Operations Against Irregular Forces, in which “irregular forces” were synonymous with Communist adversaries who were to be operated against and destroyed, an idea also found in FM 31-21: Guerrilla Warfare and Special Forces Operations (1961).5 In 1962, scholar Raymond L. Garthoff argued that IW was “the essence of Marxist-Leninist theory [and] the base of Communist strategy.”6 Also in 1962, Hugh H. Gardner published Guerrilla and Counterguerrilla Warfare in Greece, 1941-1945 (through the Office of the Chief of Military History). According to Gardner, Communist Greek partisans “employed irregular methods and their behavior cannot be judged by conventional standards.”7 While IW remained minimally or not defined, it was widely understood as the non-conventional approach used mainly by Communist guerrilla forces.

Army FM 31-15 (1961) reinforced the connection between enemy guerrilla forces and 'irregular' forces.
Army FM 31-15 (1961) reinforced the connection between enemy guerrilla forces and “irregular” forces.

Comparatively few sources claimed that the U.S. might use IW. A 1961 Office of the Secretary of Defense report advocated additional research into IW to “improve our allies’ ability to resist Communist aggression” and “provide the U.S. with increased understanding of and general capability in irregular warfare.”8 This idea was also in Joseph P. Kutger’s 1963 article, “Irregular Warfare in Transition.” Further, Kutger offered a definition of IW: “[it] comprises all those types of warfare alien to the conventional warfare … It is usually employed against an adversary as a means of minimizing his relative advantages, either in numerical strength or in the technology of his weaponry.”9 This article did not relegate IW to just enemy forces.

After Vietnam, IW’s meaning seemingly changed little, though it remained sporadically used and not defined. For example, FM 90-8: Counterguerrilla Operations (1986) made no mention of IW.10 However, things changed after the 9/11 terrorist attacks. U.S. military operations in Afghanistan and Iraq led to a spike in popularity for such terms as UW, COIN, Foreign Internal Defense (FID), stability operations (SO), nation-building, and full-spectrum operations. The term IW resurfaced and gained new prominence within the Army and DoD lexicon.

This image from U.S. Army Special Warfare (1962) depicted how farmers may become soldiers in order to wage or counter a guerrilla warfare campaign.
This image from U.S. Army Special Warfare (1962) depicted how farmers may become soldiers in order to wage or counter a guerrilla warfare campaign.

In 2005, the U.S. Joint Forces Command (USJFCOM) issued a briefing called “Historic Analysis of Lessons Learned from Modern Irregular Warfare.” It explained that IW lacked a definition but was related to such terms as COIN, UW, FID, and terrorism. It also clarified that IW was something that the U.S. might do and not just counter.11 Months later, the U.S. Special Operations Command (USSOCOM) and the Assistant Secretary of Defense for Special Operations and Low-Intensity Conflict held a workshop to draft a definition of IW, compile a list of IW activities, and build the basis for a “consensus on what [IW] is and a roadmap to incorporate IW in DoD strategic thinking.” It linked IW with UW, COIN, FID, SO, Civil-Military Operations (CMO), Psychological Operations, terrorism/counter-terrorism (CT), Information Operations, intelligence/counterintelligence, Internal Defense and Development, and even transnational crime. IW’s proposed definition was: “a warfighting philosophy aimed at achieving strategic objectives by applying or countering an approach to war that seeks to erode an adversary’s power and will, primarily through the use of indirect, non-traditional means.”12 As the DoD worked toward a definition, IW’s historic link to enemy insurgencies was eroding.

In 2006, the Deputy Secretary of Defense approved a working definition of IW: “A form of warfare that has as its objective the credibility and/or the legitimacy of … political authority with the goal of undermining or supporting that authority. [IW] favors indirect approaches, though it may employ the full range of … capabilities to seek asymmetric advantages [to] erode an adversary’s power, influence, and will.” IW’s key elements were: (a) undermining or supporting an existing political authority; (b) mostly “indirect approaches”; and (c) eroding the power, influence, and will of adversaries. This definition paved the way for future refinements.

The same year, the USMC and USSOCOM collaborated on the latest “Multi-Service Concept for Irregular Warfare,” which argued that IW aims to maintain or undermine “the legitimacy of a political authority [through] indirect approaches and nonconventional means to defeat an enemy by subversion, attrition, or exhaustion rather than direct military confrontation.” It employs “the full range of military and non-military capabilities to gain asymmetric advantages that erode an adversary’s power, influence and will until he is neutralized or defeated. IW is the preferred approach of insurgents, terrorists, and others who lack substantial conventional warfare capability as well as of nation-states who must mask their actions or whose national troops use IW in fighting irregular warriors.” This product argued that the key to U.S. victory “in the global long war in the years ahead is development of a … multi-agency capacity for irregular warfare,” one of the clearest endorsements of the need to embrace IW so far.13

On the heels of the 2008 DoD Directive 3000.07, the 2010 edition of JP 1-02 included an IW definition for the first time. Its inclusion of the qualifier 'violent struggle' did not last long.
On the heels of the 2008 DoD Directive 3000.07, the 2010 edition of JP 1-02 included an IW definition for the first time. Its inclusion of the qualifier “violent struggle” did not last long.

Within a decade after 9/11, IW had a formal definition. DoD Directive 3000.07 (2008) and Joint Publication (JP) 1-02: Department of Defense Dictionary of Military and Associated Terms (2010) defined IW as: “A violent struggle among state and non-state actors for legitimacy and influence over the relevant population(s).”14 This definition had three noteworthy aspects. First, it hearkened back to the earlier meaning by describing IW as a “violent struggle.” Second, it included state and non-state actors, meaning that virtually anyone could conduct IW. Finally, it broadened potential targets to “relevant population(s).” In other words, IW is a violent struggle between potentially anyone for legitimacy and influence over others. IW now had a definition, but its meaning was so broad as to be arguably useless.

The 2017 change to JP 1: Doctrine for the Armed Forces of the United States (2013) upheld the definition in JP 1-02 and continued to contrast IW with traditional warfare. However, it introduced a slight contradiction when it stated that in IW, “a less powerful adversary seeks to disrupt or negate the … capabilities and advantages of a more powerful military force,” but also that “most U.S. operations since the [9/11] terrorist attacks have been irregular.”15 By this description, the U.S. was the “less powerful adversary seek[ing] to disrupt or negate the … capabilities and advantages of a more powerful military force,” which was not true in Afghanistan or Iraq. This was indicative of the challenge of stabilizing IW’s meaning after 9/11.

In the IW annex to the 2018 National Defense Strategy, IW is explained as 'a struggle among state and non-state actors to influence populations and affect legitimacy,' a marked departure from the term's Cold War-era roots.
In the IW annex to the 2018 National Defense Strategy, IW is explained as “a struggle among state and non-state actors to influence populations and affect legitimacy,” a marked departure from the term’s Cold War-era roots.

By the 2010s, the U.S. had entered a new era of strategic competition. The 2018 National Defense Strategy (NDS) signaled the pivot away from C-VEO to Great (or Global) Power Competition with other major powers, namely China and Russia. The NDS led to the Irregular Warfare Annex to the National Defense Strategy in February 2019, followed by the more widely publicized Summary of the Irregular Warfare Annex to the National Defense Strategy. These explained IW as “a struggle among state and non-state actors to influence populations and affect legitimacy” (dropping the qualifier “violent struggle”). According to the summary, “IW favors indirect and asymmetric approaches, though it may employ the full range of military and other capabilities” against an adversary. The list of IW-related activities had broadened further to include such activities as UW, FID, CT, COIN, CMO, stabilization, military information support operations (MISO), cyber operations, countering threat networks (CTN), and counter-threat finance (CTF).16 IW’s entanglement with other terms continued to complicate things (adding to the potential confusion with Information Warfare, also shortened to IW). IW had reached peak importance, but its meaning was broad, vague, and fluid; it could mean anything (mostly non-conventional) done by anyone to influence, delegitimize, or defeat anyone else.

A Ukrainian Special Forces (SF) soldier and a U.S. Army 10th SFG soldier move to an observation post during Exercise COMBINED RESOLVE 16 in Hohenfels, Germany, 8 December 2021. The exercise was designed to assess the readiness of the 1st Armored Brigade Combat Team, 1st Infantry Division, while providing opportunities for SOF soldiers from the Ukraine, U.S., and Lithuania to hone irregular warfare skills.
A Ukrainian Special Forces (SF) soldier and a U.S. Army 10th SFG soldier move to an observation post during Exercise COMBINED RESOLVE 16 in Hohenfels, Germany, 8 December 2021. The exercise was designed to assess the readiness of the 1st Armored Brigade Combat Team, 1st Infantry Division, while providing opportunities for SOF soldiers from the Ukraine, U.S., and Lithuania to hone irregular warfare skills.

In 2021, the J-7, Joint Staff, published its “Irregular Warfare Mission Analysis,” the “first comprehensive review of [IW] since 2007. The global strategic environment has significantly shifted … and the [DoD’s concept] of what [IW] is and how to employ it must shift also.” Contrary to older characterizations of IW, this report argued that IW “is as strategically important as traditional warfare.” It conceded that “IW is … complex, messy, and ambiguous,” and “does not lend itself to clean, neat, concise, or precise definition.” Though it did not define IW, it reiterated its ties with CT, UW, FID, COIN, and SO. Ironically, it called this association “confusing and counterproductive” before listing even more IW-related activities, such as UW, FID, CT, COIN, CTN, CTF, CMO, stability activities, MISO, and Civil Affairs, among others.17 This mission analysis did little to clarify IW’s meaning, but it was a major step toward reimaging IW in GPC and initiating what has been described as a DoD-wide “mindset shift” toward IW.

Fittingly, the Army G-3/5/7 assigned the U.S. Army Special Operations Command as the IW proponent in February 2022. It was to develop “the necessary doctrine, training, leadership and education, personnel concepts and tenets for [UW], [CT], [COIN], and [FID].”18 Meanwhile, IW would retain flexible meaning across the DoD. For example, USSOCOM’s Special Operations Forces Vision and Strategy (2022) frequently used but did not clarify such terms as “irregular threats,” IW capabilities, nor IW writ large.19

Members of the 320th Special Tactics Squadron, Royal Thai Army, share mountaineering techniques with their U.S. Army 1st Special Forces Group (SFG) counterparts in Thailand, 20 April 2022. A strong, forward-looking American-Thai defense alliance bolsters the U.S. national defense strategy of countering near-peer threats in the Indo-Pacific region.
Members of the 320th Special Tactics Squadron, Royal Thai Army, share mountaineering techniques with their U.S. Army 1st Special Forces Group (SFG) counterparts in Thailand, 20 April 2022. A strong, forward-looking American-Thai defense alliance bolsters the U.S. national defense strategy of countering near-peer threats in the Indo-Pacific region.

In conclusion, over time, IW has become more popular and well-defined, but its meaning has become more fluid and ambiguous since 9/11. It went from describing Communist-inspired guerrilla insurgencies in the Cold War to a broad military-governmental approach against peer threats in GPC into the 2020s. It has expanded from a tactical focus to a strategic focus. It remains inseparable from such popular terms as UW, COIN, and FID, while its definition remains sufficiently vague to allow for great variances in interpretation. The question remains—will the popularity of the term IW force the DoD to further refine its meaning, or will it remain nebulous to allow greater flexibility in discussing and addressing the challenges of the modern international environment?

Epilogue

As this article was being finalized for publication in Veritas, the Army released the latest edition of FM 3-0: Operations (October 2022). This manual continued the post-9/11 trend of refining the definition of IW while leaving actual meaning up for interpretation. According to this manual, IW is the “overt, clandestine, and covert employment of military and non-military capabilities across multiple domains by state and non-state actors through methods other than military domination of an adversary, either as the primary approach or in concert with conventional warfare.”20 The most concrete aspect of this description is that IW is something other than “military domination of an adversary.” Otherwise, it remains flexible enough to accommodate a variety of interpretations and applications.

ENDNOTES

  1. This article lists only a representative sample of official documents since the early 1950s. There were dozens of others researched that made little or no mention of IW or “irregular” in general and which therefore have been omitted. The author acknowledges that the interpretations within this article, while based on relevant evidence, are tentative since not all official documents have researched. It is possible, though unlikely, that further investigation into additional DoD documents may yield significantly different results and change the overall conclusion of this paper. In addition, although the abbreviation IW is used throughout this article, it should be noted that until relatively recently, publications typically used the term “irregular warfare” in a more general sense (not capitalized) as opposed to its later formal codification as Irregular Warfare (capitalized). [return]
  2. Headquarters, Department of the Army (HQDA), FM 31-20: Operations Against Guerrilla Forces (Washington, DC: HQDA, February 1951), iii. [return]
  3. HQDA, FM 31-21: Organization and Conduct of Guerrilla Warfare (Washington, DC: HQDA, October 1951), 2. [return]
  4. USASWCS, “Readings in Counter-Guerrilla Operations” (17 January 1961), copy in USASOC History Office, Fort Bragg, NC. [return]
  5. HQDA, FM 31-15: Operations Against Irregular Forces (Washington, DC: HQDA, May 1961), 3; HQDA, FM 31-21: Guerrilla Warfare and Special Forces Operations (Washington, DC: HQDA, 29 September 1961), 9. [return]
  6. School of Resident Studies, Industrial College of the Armed Forces, “Insurgency and Counterinsurgency: An Anthology” (October 1962), 151-152, copy in USASOC History Office, Fort Bragg, NC. [return]
  7. Hugh H. Gardner, Office of the Chief of Military History, Guerrilla and Counterguerrilla Warfare in Greece, 1941-1945 (Washington, DC: HQDA, 1962), 145. [return]
  8. Director of Defense Research and Engineering, Office of the Secretary of Defense, Report of the RDT&E Limited War Task Group (15 August 1961), 31-32, copy in USASOC History Office, Fort Bragg, NC, emphasis added. [return]
  9. Air Training Command, U.S. Air Force, “Anthology of Related Topics on Counterinsurgency, Volume I: Irregular Warfare in Transition” (1 March 1963), 1, copy in USASOC History Office, Fort Bragg, NC. [return]
  10. HQDA, FM 90-8: Counterguerrilla Operations (Washington, DC: HQDA, August 1986), copy in USASOC History Office, Fort Bragg, NC. [return]
  11. U.S. Joint Forces Command, “Historic Analysis of Lessons Learned from Modern Irregular Warfare” (10 June 2005), copy in USASOC History Office, Fort Bragg, NC. [return]
  12. USSOCOM and ASD (SO/LIC), “Irregular Warfare Workshop Outbrief” (September 2005), copy in USASOC History Office, Fort Bragg, NC. [return]
  13. U.S. Marine Corps Combat Development Command and USSOCOM Center for Knowledge and Futures, “Multi-Service Concept for Irregular Warfare” (2 August 2006), 7, copy in USASOC History Office, Fort Bragg, NC. [return]
  14. DoDD 3000.07, “SUBJECT: Irregular Warfare” (1 December 2008), https://www.tecom.marines.mil/Portals/162/Docs/DOD%20Directive%203000.07%20IW.pdf; Joint Staff, JP 1-02: Department of Defense Dictionary of Military and Associated Terms (Washington, DC: Joint Staff, 8 November 2010, as amended through 15 November 2014), 130 [return]
  15. Joint Staff, JP 1: Doctrine for the Armed Forces of the United States (Washington, DC: Joint Staff, 25 March 2013, Incorporating Change 1, 12 July 2017), x, 1-5. [return]
  16. Department of Defense, Summary of the Irregular Warfare Annex to the [2018] National Defense Strategy (2020), 2, https://media.defense.gov/2020/Oct/02/2002510472/-1/-1/0/Irregular-Warfare-Annex-to-the-National-Def. [return]
  17. Office of Irregular Warfare and Competition, Joint Force Development and Design Directorate (J-7), Joint Staff, “Irregular Warfare Mission Analysis” (19 October 2021), Foreword, 3, 6, copy in USASOC History Office, Fort Bragg, NC. [return]
  18. Department of the Army G-3/5/7, “SUBJECT: Designation of Commander, U.S. Army Special Operations Command as the Army Functional Proponent for Irregular Warfare,” 28 February 2022, copy in USASOC History Office, Fort Bragg, NC. [return]
  19. USSOCOM, Special Operations Forces Vision and Strategy (MacDill AFB, FL: USSOCOM, 2022), 1, 5-6. [return]
  20. HQDA, FM 3-0: Operations (Washington, DC: HQDA, October 2022), Glossary-8, https://armypubs.army.mil/epubs/DR_pubs/DR_a/ARN36290-FM_3-0-000-WEB-2.pdf. [return]