How many troops are needed to defeat an insurgency? This deceptively innocuous question is laden with political and military peril. The answer is, of course, that it depends. Some contend that a precise ratio of counterinsurgents to insurgents or to the local population will lead to victory, while others argue that force strengths are irrelevant to success or failure. In the wake of America’s decidedly ambivalent experiences in Iraq and Afghanistan, the debate remains unresolved. However, there have been several recent analytical efforts focused on resolving the question. This will be the first in a series of posts that will review these studies and their conclusions.
It is not clear where the notion originated that force ratios mattered in counterinsurgency. It appears to have become an article of faith during the British campaign in Malaya, although Sir Robert Thompson — a British staff officer in that conflict and a counterinsurgency theorist influential during the Vietnam War — subsequently claimed that the rule-of-thumb that 20 troops were needed per 1,000 insurgents to succeed was the invention of a journalist.[1] Another Mayalan campaign veteran, Richard Clutterbuck, likewise later derided the validity of a “tie-down” ratio:
Much nonsense is heard on the subject of tie-down ratios in guerrilla warfare–that 10 to 12 government troops are needed to tie down a single guerrilla, for instance. This is a dangerous illusion, arising from a disregard of the facts.[2]
The relevance of force ratios made a comeback in the mid-1990s, albeit measured in a different way. Seeking a way of projecting force requirements necessary for sustained stability operations, RAND analyst James T. Quinliven looked at 13 historical cases and concluded that success required 20 troops were needed per 1,000 local inhabitants.[3] Defining ratios by the number of troops per population became known as force density.
The political volatility of force requirements for stability operations and counterinsurgency became vividly apparent during the lead up to the U.S. invasion of Iraq in 2003. Quinlivan published an update of his analysis to address Iraq and asserted that to meet a ratio of 20 troops per 1,000 inhabitants, 500,000 foreign troops were necessary to stabilize 25 million Iraqis.[4] U.S. Army Chief of Staff General Eric Shinseki told Congress that “several hundred thousand” American troops would be necessary to stabilize Iraq following the fall of Saddam Hussein. This drew a quick rebuttal from Deputy Secretary of Defense Paul Wolfowitz, who testified that Shinseki’s estimate was “wildly off the mark.” The public disagreement led to Shinseki’s premature retirement and replacement as Army Chief of Staff.
Although the initial phase of Operation IRAQI FREEDOM quickly defeated the Iraqi military and toppled Saddam’s regime, the chaotic stabilization effort that followed and the emergence of an insurgency appeared to bear out the validity of Qunilivan’s and Shinseki’s assessments for force requirements. Certainly one influential group thought so: the authors of the revised U.S. Army and Marine Corps doctrinal manual FM 3-24/MCWP 3-33.5 Counterinsurgency, published in 2006. The manual rejected tie-down ratios but endorsed Quinlivan’s force density concept:
During previous conflicts, planners assumed that combatants required a 10 or 15 to 1 advantage over insurgents to win. However, no predetermined, fixed ratio of friendly troops to enemy combatants ensures success in COIN. The conditions of the operational environment and the approaches insurgents use vary too widely. A better force requirement gauge is troop density, the ratio of security forces (including the host nation’s military and police forces as well as foreign counterinsurgents) to inhabitants. Most density recommendations fall within a range of 20 to 25 counterinsurgents for every 1000 residents in an AO. Twenty counterinsurgents per 1000 residents is often considered the minimum troop density required for effective COIN operations; however as with any fixed ratio, such calculations remain very dependent upon the situation.[5]
FM 3-24 was often cited as the intellectual foundation for the subsequent success of the so-called Iraqi “Surge” in 2007 under General David Petraeus, who had overseen revision of the manual as the commander of the U.S. Army’s Combined Arms Center at Ft. Leavenworth.
Interestingly enough, however, this endorsement of force density ratios was qualified in the subsequent joint doctrinal manual, JP 3-24 Counterinsurgency Operations, published just three years later in 2009. While force density was still considered a useful measure, mention of the specific 20/1,000 ratio was omitted:
No force level guarantees victory for either side, insurgent or counterinsurgent. No predetermined, fixed ratio of friendly forces to enemy forces ensures success in COIN. The OE and insurgents’ approaches vary too widely. Such calculations remain very dependent upon the assets available and the situation. A better force requirement gauge is counterinsurgent force density, which is the ratio of land security forces (including both indigenous and foreign contributions) and supporting elements (which must account for technological sophistication and applicability) to inhabitants. Force density will depend on the overall context, especially the size and density of the population, and can change over time. In some situations, the necessary force ratio may be unattainable. In these situations, the commander will have to determine if there are ways to leverage other advantages through innovative operational design and interdependent joint operations. If not, this may lead the commander to adopt limited objectives or plan for a prolonged, multiphased campaign as alternatives.[6]
When JP 3-24 and FM 3-24 were again revised in 2013 and 2014, respectively, neither contained any references to force level requirements, tie-down ratios, or troop density.[7] As quickly as the concepts had been adopted, they were abandoned. This is likely the result of more careful examinations of the relationship between force strength and counterinsurgency outcomes conducted during the 2000s. I will take a closer look at these studies in subsequent posts.
Additional posts in this series:
Force Ratios and Counterinsurgency II
Force Ratios and Counterinsurgency III
Force Ratios and Counterinsurgency IV
Notes
[1] Riley M. Moore, “Counterinsurgency Force Ratio: Strategic Utility or Nominal Necessity,” Small Wars & Insurgencies, 24:5, 2013, p. 859
[2] Christopher A.Lawrence, America’s Modern Wars: Understanding Iraq, Afghanistan and Vietnam, Philadelphia, PA: Casemate, 2015, p. 55
[3] James T. Quinlivan, “Force Requirements in Stability Operations,” Parameters 25, no. 4, 1995, p. 59–69
[4] James T. Quinlivan, “Burden of Victory: the Painful Arithmetic of Stability Operations,” Santa Monica, CA: Rand Corporation, 2003
[5] Field Manual (FM) 3-24 Counterinsurgency, Washington, DC: Headquarters, Department of the Army, December 2006, p. I-13
[6] Joint Publication (JP) 3-24 Counterinsurgency Operations, Washington, DC: Joint Staff of the Joint Chiefs of Staff, 5 October 2009, p. III-3
[7] Joint Publication (JP) 3-24 Counterinsurgency, Washington, DC: Joint Staff of the Joint Chiefs of Staff, 22 November 2013; Field Manual (FM) 3-24 Insurgencies and Countering Insurgencies, Washington, DC: Headquarters, Department of the Army, May 2014
