What Did James Mattis Mean by “Lethality?”

Then-Lt. Gen. James Mattis, commander of U.S. Marine Corps Forces, Central Command, speaks to Marines with Marine Wing Support Group 27, in Al Asad, Iraq, in May 2006. [Photo: Cpl. Zachary Dyer]

Ever since publication of the U.S. National Defense Strategy by then-Secretary of Defense James Mattis’s Defense Department in early 2018 made the term “lethality” a foundational principle, there has been an open-ended discussion as to what the term actually means.

In his recent memoir, co-written with Bing West, Call Sign Chaos: Learning to Lead (Random House, 2019), Mattis offered his own definition of lethality. Sort of.

At the beginning of Chapter 17 (pages 235-236), he wrote (emphasis added):


History presents many examples of militaries that forgot that their purpose was to fight and win. So long as we live in an imperfect world, one containing enemies of democracy, we will need a military strictly committed to combat-effectiveness. Our liberal democracy must be protected by a bodyguard of lethal warriors, organized, trained, and equipped to dominate in battle.

The need for lethality must be the measuring stick against which we evaluate the efficacy of our military. By aligning the entire military enterprise—recruiting, training, educating, equipping, and promoting—to the goal of compounding lethality, we best deter adversaries, or if conflict occurs, win at lowest cost to our troops’ lives. …

While not defining lethality explicitly, it would appear that Mattis equates it with “combat-effectiveness,” which he also does not explicitly define, but seems to mean as the ability “to dominate in battle.” It would seem that Mattis understands lethality not as the destructive quality of a weapon or weapon system, but as the performance of troops in combat.

More than once he also refers to lethality as a metric, which suggests that it can be quantified and measured, perhaps in terms of organization, training, and equipment. It is likely Mattis would object to that interpretation, however, given his hostility to Effects Based Operations (EBO), as implemented by U.S. Joint Forces Command, before he banned the concept from joint doctrine in 2008, as he related on pages 179-181 in Call Sign Chaos.

Trevor Dupuy’s Definitions of Lethality

Two U.S. Marines with a M1919A4 machine gun on Roi-Namur Island in the Marshall Islands during World War II. [Wikimedia]

It appears that discussion of the meaning of lethality, as related to the use of the term in the 2018 U.S. National Defense Strategy document, has sparked up again. It was kicked off by an interesting piece by Olivia Gerard in The Strategy Bridge last autumn, “Lethality: An Inquiry.

Gerard credited Trevor Dupuy and his colleagues at the Historical Evaluation Research Organization (HERO) with codifying “the military appropriation of the concept” of lethality, which was defined as: “the inherent capability of a given weapon to kill personnel or make materiel ineffective in a given period, where capability includes the factors of weapon range, rate of fire, accuracy, radius of effects, and battlefield mobility.”

It is gratifying for Gerard to attribute this to Dupuy and HERO, but some clarification is needed. The definition she quoted was, in fact, one provided to HERO for the purposes of a study sponsored by the Advanced Tactics Project (AVTAC) of the U.S. Army Combat Developments Command. The 1964 study report, Historical Trends Related to Weapon Lethality, provided the starting point for Dupuy’s subsequent theorizing about combat.

In his own works, Dupuy used a simpler definition of lethality:

He also used the terms lethality and firepower interchangeably in his writings. The wording of the original 1964 AVTAC definition tracks closely with the lethality scoring methodology Dupuy and his HERO colleagues developed for the study, known as the Theoretical Lethality Index/Operational Lethality Index (TLI/OLI). The original purpose of this construct was to permit some measurement of lethality by which weapons could be compared to each other (TLI), and to each other through history (OLI). It worked well enough that he incorporated it into his combat models, the Quantified Judgement Model (QJM) and Tactical Numerical Deterministic Model (TNDM).

The Hierarchy of Combat

The second conceptual element in Trevor Dupuy’s theory of combat is his definition of the hierarchy of combat:

[F]ghting between armed forces—while always having the characteristics noted [in the definition of military combat], such as fear and planned violence—manifests itself in different fashions from different perspectives. In commonly accepted military terminology, there is a hierarchy of military combat, with war as its highest level, followed by campaign, battle, engagement, action, and duel.

A war is an armed conflict, or a state of belligerence, involving military combat between two factions, states, nations, or coalitions. Hostilities between the opponents may be initiated with or without a formal declaration by one or both parties that a state of war exists. A war is fought for particular political or economic purposes or reasons, or to resist an enemy’s efforts to impose domination. A war can be short, sometimes lasting a few days, but usually is lengthy, lasting for months, years, or even generations.

A campaign is a phase of a war involving a series of operations related in time and space and aimed toward achieving a single, specific, strategic objective or result in the war. A campaign may include a single battle, but more often it comprises a number of battles over a protracted period of time or a considerable distance, but within a single theater of operations or delimited area. A campaign may last only a few weeks, but usually lasts several months or even a year.

A battle is combat between major forces, each having opposing assigned or perceived operational missions, in which each side seeks to impose its will on the opponent by accomplishing its own mission, while preventing the opponent from achieving his. A battle starts when one side initiates mission-directed combat and ends when one side accomplishes its mission or when one or both sides fail to accomplish the mission(s). Battles are often parts of campaigns. Battles between large forces usually are made up of several engagements, and can last from a few days to several weeks. Naval battles tend to be short and—in modern times—decisive.

An engagement is combat between two forces, neither larger than a division nor smaller than a company, in which each has an assigned or perceived mission. An engagement begins when the attacking force initiates combat in pursuit of its mission and ends when the attacker has accomplished the mission, or ceases to try to accomplish the mission, or when one or both sides receive significant reinforcements, thus initiating a new engagement. An engagement is often part of a battle. An engagement normally lasts one or two days; it may be as brief as a few hours and is rarely longer than five days.

An action is combat between two forces, neither larger than a battalion nor smaller than a squad, in which each side has a tactical objective. An action begins when the attacking force initiates combat to gain its objective, and ends when the attacker wins the objective, or one or both forces withdraw, or both forces terminate combat. An action often is part of an engagement and sometimes is part of a battle. An action lasts for a few minutes or a few hours and never lasts more than one day.

A duel is combat between two individuals or between two mobile fighting machines, such as combat vehicles, combat helicopters, or combat aircraft, or between a mobile fighting machine and a counter-weapon. A duel begins when one side opens fire and ends when one side or both are unable to continue firing, or stop firing voluntarily. A duel is almost always part of an action. A duel lasts only a few minutes. [Dupuy, Understanding War, 64-66]

Trevor Dupuy’s Definition of Military Combat

Ernst Zimmer: “Das Lauenburgische Jäger-Bataillon Nr. 9 bei Gravelotte” [Wikipedia]

The first element in Trevor Dupuy’s theory of combat is his definition of military combat:

I define military combat as a violent, planned form of physical interaction (fighting) between two hostile opponents, where at least one party is an organized force, recognized by governmental or de facto authority, and one or both opposing parties hold one or more of the follow-on objectives: to seize control of territory or people; to prevent the opponent from seizing or controlling territory or people; to protect one’s own territory or people; to dominate, destroy, or incapacitate the opponent.

The impact of weapons creates an environment of lethality, danger, and fear in which achievement of the objectives by one party may require the opponent to choose among: continued resistance and resultant destruction; retreat and loss of territory, facilities, and people; surrender. Military combat begins in any interaction, or at any level of combat from duel to full-scale war, when weapons are first employed with hostile intent by one or both opponents.  Military combat ends for any interaction or level of combat when both sides have stopped fighting.

There are two key points in this definition that I wish to emphasize. Though there may be much in common between military combat and a brawl in a barroom, there are important differences. The opponents in military combat are to some degree organized, and both represent a government or quasi-governmental authority. There is one other essential difference: the all-pervasive influence of fear in a lethal environment. People have been killed in barroom brawls, but this is exceptional. In military combat there is the constant danger of death from lethal weapons employed by opponents with deadly intent. Fear is without question the most important characteristic of combat. [Dupuy, Understanding War, 63-64]

The Elements of Trevor Dupuy’s Theory of Combat

Trevor Dupuy’s combat models (the Quantified Judgement Model (QJM) and the Tactical Numerical Deterministic Model (TNDM)) are formal expressions of his theory of combat. Dupuy provided an extensive discussion of the basis for his theory in his books, particularly Understanding Combat: History and Theory of Combat (NOVA Publications, 1987). While many are familiar with his models, fewer are aware of the concepts that he based it upon. This will be the first in a series of posts looking at those elements.

As Dupuy explained,

As a starting point for an explanation of a scientific theory, it is useful to define fundamental terms, to state and explain critical assumptions, and to establish—or limit—the scope of the discussion that follows. The definitions and explanations that follow are generally consistent with usage in the military and analytical communities, and with definitions that have been formulated for its work by The Military Conflict Institute. However, I have in some instances modified or restated these to conform to my own ideas and usage. [Dupuy, Understanding Combat, 63]

The basic elements of his theory of combat are:

Definition of Military Combat
The Hierarchy of Combat
The Conceptual Components of Combat
The Scope of Theory
Definition of a Theory of Combat

These will each be discussed in future posts.

Dupuy’s Verities: The Complexities of Combat

“The Battle of Leipzig, 16-19 October 1813” by A.I. Zauerweid (1783-1844) [Wikimedia]

The thirteenth and last of Trevor Dupuy’s Timeless Verities of Combat is:

Combat is too complex to be described in a single, simple aphorism.

From Understanding War (1987):

This is amply demonstrated by the preceding [verities]. All writers on military affairs (including this one) need periodically to remind themselves of this. In military analysis it is often necessary to focus on some particular aspect of combat. However, the results of such closely focused analyses must the be evaluated in the context of the brutal, multifarious, overlapping realities of war.

Trevor Dupuy was sometimes accused of attempting to reduce war to a mathematical equation. A casual reading of his writings might give that impression, but anyone who honestly engages with his ideas quickly finds this to be an erroneous conclusion. Yet, Dupuy believed the temptation to simplify and abstract combat and warfare to be common enough that he he embedded a warning against doing so into his basic theory on the subject. He firmly believed that human behavior comprises the most important aspect of combat, yet it is all too easy to miss the human experience of war figuring who lost or won and why, and counts of weapons, people, and casualties. As a military historian, he was keenly aware that the human stories behind the numbers—however imperfectly recorded and told—tell us more about the reality of war than mere numbers on their own ever will.

Dupuy’s Verities: Combat Power =/= Firepower

A U.S. 11th Marines 75mm pack howitzer and crew on Guadalcanal, September or October, 1942. The lean condition of the crewmembers indicate that they haven’t been getting enough nutrition during this period. [Wikipedia]

The ninth of Trevor Dupuy’s Timeless Verities of Combat is:

Superior Combat Power Always Wins.

From Understanding War (1987):

Military history demonstrates that whenever an outnumbered force was successful, its combat power was greater than that of the loser. All other things being equal, God has always been on the side of the heaviest battalions and always will be.

In recent years two or three surveys of modern historical experience have led to the finding that relative strength is not a conclusive factor in battle outcome. As we have seen, a superficial analysis of historical combat could support this conclusion. There are a number of examples of battles won by the side with inferior numbers. In many battles, outnumbered attackers were successful.

These examples are not meaningful, however, until the comparison includes the circumstances of the battles and opposing forces. If one take into consideration surprise (when present), relative combat effectiveness of the opponents, terrain features, and the advantage of defensive posture, the result may be different. When all of the circumstances are quantified and applied to the numbers of troops and weapons, the side with the greater combat power on the battlefield is always seen to prevail.

The concept of combat power is foundational to Dupuy’s theory of combat. He did not originate it; the notion that battle encompasses something more than just “physics-based” aspects likely originated with British theorist J.F.C. Fuller during World War I and migrated into U.S. Army thinking via post-war doctrinal revision. Dupuy refined and sharpened the Army’s vague conceptualization of it in the first iterations of his Quantified Judgement Model (QJM) developed in the 1970s.

Dupuy initially defined his idea of combat power in formal terms, as an equation in the QJM:

P = (S x V x CEV)


P = Combat Power
S = Force Strength
V = Environmental and Operational Variable Factors
CEV = Combat Effectiveness Value

Essentially, combat power is the product of:

  • force strength as measured in his models through the Theoretical/Operational Lethality Index (TLI/OLI), a firepower scoring method for comparing the lethality of weapons relative to each other;
  • the intangible environmental and operational variables that affect each circumstance of combat; and
  • the intangible human behavioral (or moral) factors that determine the fighting quality of a combat force.

Dupuy’s theory of combat power and its functional realization in his models have two virtues. First, unlike most existing combat models, it incorporates the effects of those intangible factors unique to each engagement or battle that influence combat outcomes, but are not readily measured in physical terms. As Dupuy argued, combat consists of more than duels between weapons systems. A list of those factors can be found below.

Second, the analytical research in real-world combat data done by him and his colleagues allowed him to begin establishing the specific nature combat processes and their interaction that are only abstracted in other combat theories and models. Those factors and processes for which he had developed a quantification hypothesis are denoted by an asterisk below.

Dupuy’s Verities: The Inefficiency of Combat

The “Mud March” of the Union Army of the Potomac, January 1863.

The twelfth of Trevor Dupuy’s Timeless Verities of Combat is:

Combat activities are always slower, less productive, and less efficient than anticipated.

From Understanding War (1987):

This is the phenomenon that Clausewitz called “friction in war.” Friction is largely due to the disruptive, suppressive, and dispersal effects of firepower upon an aggregation of people. This pace of actual combat operations will be much slower than the progress of field tests and training exercises, even highly realistic ones. Tests and exercises are not truly realistic portrayals of combat, because they lack the element of fear in a lethal environment, present only in real combat. Allowances must be made in planning and execution for the effects of friction, including mistakes, breakdowns, and confusion.

While Clausewitz asserted that the effects of friction on the battlefield could not be measured because they were largely due to chance, Dupuy believed that its influence could, in fact, be gauged and quantified. He identified at least two distinct combat phenomena he thought reflected measurable effects of friction: the differences in casualty rates between large and small sized forces, and diminishing returns from adding extra combat power beyond a certain point in battle. He also believed much more research would be necessary to fully understand and account for this.

Dupuy was skeptical of the accuracy of combat models that failed to account for this interaction between operational and human factors on the battlefield. He was particularly doubtful about approaches that started by calculating the outcomes of combat between individual small-sized units or weapons platforms based on the Lanchester equations or “physics-based” estimates, then used these as inputs for brigade and division-level-battles, the results of which in turn were used as the basis for determining the consequences of theater-level campaigns. He thought that such models, known as “bottom up,” hierarchical, or aggregated concepts (and the prevailing approach to campaign combat modeling in the U.S.), would be incapable of accurately capturing and simulating the effects of friction.

Dupuy’s Verities: The Effects of Firepower in Combat

A German artillery barrage falling on Allied trenches, probably during the Second Battle of Ypres in 1915, during the First World War. [Wikimedia]

The eleventh of Trevor Dupuy’s Timeless Verities of Combat is:

Firepower kills, disrupts, suppresses, and causes dispersion.

From Understanding War (1987):

It is doubtful if any of the people who are today writing on the effect of technology on warfare would consciously disagree with this statement. Yet, many of them tend to ignore the impact of firepower on dispersion, and as a consequence they have come to believe that the more lethal the firepower, the more deaths, disruption, and suppression it will cause. In fact, as weapons have become more lethal intrinsically, their casualty-causing capability has either declined or remained about the same because of greater dispersion of targets. Personnel and tank loss rates of the 1973 Arab-Israeli War, for example, were quite similar to those of intensive battles of World War II and the casualty rates in both of these wars were less than in World War I. (p. 7)

Research and analysis of real-world historical combat data by Dupuy and TDI has identified at least four distinct combat effects of firepower: infliction of casualties (lethality), disruption, suppression, and dispersion. All of them were found to be heavily influenced—if not determined—by moral (human) factors.

Again, I have written extensively on this blog about Dupuy’s theory about the historical relationship between weapon lethality, dispersion on the battlefield, and historical decline in average daily combat casualty rates. TDI President Chris Lawrence has done further work on the subject as well.

TDI Friday Read: Lethality, Dispersion, And Mass On Future Battlefields

Human Factors In Warfare: Dispersion

Human Factors In Warfare: Suppression

There appears to be a fundamental difference in interpretation of the combat effects of firepower between Dupuy’s emphasis on the primacy of human factors and Defense Department models that account only for the “physics-based” casualty-inflicting capabilities of weapons systems. While U.S. Army combat doctrine accounts for the interaction of firepower and human behavior on the battlefield, it has no clear method for assessing or even fully identifying the effects of such factors on combat outcomes.

A Comment On The Importance Of Reserves In Combat

An German Army A7V near the Somme on March 26, 1918 [forces.net] Operation Michael was the first of a series of German Army offensives on the Western Front in the spring of 1918. In late March, 74 German divisions employing infiltration tactics created a breach in a sector of the line held by the British Army. The Germans advanced up to 40 miles and captured over 75,000 British soldiers, but the ability of the British and French to redeploy reserves via rail halted the offensive in early April short of strategic success.

In response to my previous post on Trevor Dupuy’s verity regarding the importance of depth and reserves for successful defense, a commenter posed the following question: “Is the importance of reserves mainly in its own right, or to mitigate the advantages of attacker surprise?”

The importance of reserves to both attacker and defender is as a hedge against the circumstantial uncertainties of combat. Reserves allow attacking and defending commanders the chance to maintain or regain initiative in response to the outcomes of battle. The side that commits its last reserves before its opponent does concedes the initiative to the enemy, probably irrevocably.

In Trevor Dupuy’s theory of combat, the intrinsic superiority of the defensive posture (as per Clausewitz) is the corollary to the attacker’s inherent advantage in initiative. When combined with the combat multipliers of favorable terrain and prepared positions or fortifications, the combat power of a defending force is greatly enhanced. This permits a defending commander to reap the benefit of economy of force to create reserves. When arrayed in sufficient depth to prevent an attacker from engaging them, reserves grant flexibility of response to the defender. A linear defense or improperly placed reserves concede this benefit to the attacker at the outset, permitting the attacking commander to exploit initiative to mass superior combat power at a decisive point without reserves to interfere.

A defender’s reserves are certainly useful in mitigating attacker surprise, but in Dupuy’s theories and models, surprise is a combat multiplier available to both attacker and defender. As perhaps the most powerful combat multiplier available on the battlefield, surprise in the form of a well-timed counterattack by a defender can devastate an attacking force. Even an unexpected tactical wrinkle by a defender can yield effective surprise.