PDF Summary:On Combat, by Dave Grossman and Loren W. Christensen

Combat takes a profound psychological and physiological toll on those who experience it. In On Combat, Dave Grossman and Loren W. Christensen examine how stress affects soldiers and law enforcement officers in life-threatening situations. They explain that the fear of interpersonal aggression is deeply rooted in human nature, and that combat stress has historically caused more casualties than enemy fire itself. The authors detail how stress triggers automatic bodily responses that can distort perception, impair memory, and compromise performance.

Grossman and Christensen also explore methods for building resilience against combat stress. They discuss how realistic training, controlled breathing techniques, and mental preparation can help warriors manage stress responses. Additionally, they emphasize the importance of organizational support, effective leadership, and team-based tactics in helping combatants perform under pressure and recover afterward.

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(Shortform note: A correlation coefficient is a single number that describes the strength of a relationship between two variables. In this case, the variables are the presence of a perceptual distortion just before shooting and the presence of the same distortion while shooting. The coefficient ranges from -1 to +1. A coefficient of +1 indicates a perfect positive correlation, meaning that as one variable increases, the other variable also increases in a perfectly linear relationship. A coefficient of -1 indicates a perfect negative correlation, meaning that as one variable increases, the other variable decreases in a perfectly linear relationship. A coefficient of 0 indicates no correlation between the variables.)

These figures suggest that when people experienced heightened visual clarity in one time frame—either before or after—they probably experienced it in the other as well (r = .61). If they heard sounds more intensely during one period, they're not especially prone to experiencing more intense sound in the other timeframe (r = .14). The authors add that having a sensation of sped-up time before shooting correlates with sound being heightened both beforehand (correlation coefficient of .24) and during the act (correlation coefficient of .25).

(Shortform note: The authors don’t explain how a sensation of sped-up time could be connected to heightened sound. However, Sylvie Droit-Volet and Warren H. Meck suggest that the brain circuits that track time also modulate the strength of sensory signals. When these circuits enter a high-gain state, they can make time feel faster and sounds feel louder. This could explain why people who feel time speeding up before shooting also report heightened sound both before and during the act.)

People who experienced accelerated motion perception when shooting were a bit more likely to notice amplified sound both before (r = .30) and during (r = .28) firing. If the sound diminished before shooting, it was more likely that officers would also perceive time in slow motion, both while firing (r = .24) and during it (r = .28). They also mention additional connections, like the link between tunnel vision and decreased sound during shooting (correlation coefficient: .29), and the relationship between perceiving reduced speed and decreased sound before firing (correlation coefficient: .28).

(Shortform note: Why do these correlations matter? According to Mica R. Endsley, a leading expert on situation awareness, understanding the patterns of information acquisition and loss in dynamic tasks is crucial for developing effective training and equipment. These correlations help researchers identify stable patterns in how perception changes under stress, which in turn informs the design of training programs and equipment that can help officers maintain better situation awareness during high-stress encounters.)

They also note negative correlations, where the rise or increased likelihood of one element coincides with the decrease or diminished likelihood of another. As an example, having tunnel vision before firing is less likely to happen along with increased visual detail (r = -.38); this negative correlation also applies during firing (r = -.27). Thus, the authors believe that increased visual acuity tends to make tunnel vision less likely.

Tunnel Vision Before Firing

Tunnel vision before firing refers to a stress-induced narrowing of an officer’s visual field, where their attention becomes intensely focused on a small central area, often the perceived threat or target, while peripheral awareness diminishes. This phenomenon can occur in high-stress situations, such as before discharging a firearm, where the officer’s brain prioritizes the most immediate and relevant visual information to enhance survival. While this can help officers concentrate on the threat, it may also cause them to miss important details in their surroundings.

Cognitive Effects and Recovery Due to Stressors From War

Grossman and Christensen note that combat stress can cause perceptual distortions and memory loss. Perceptual distortions are changes in the way you see and hear things, while memory loss is when you forget parts of what happened. These occur because combat stress causes changes in your body that affect vision and hearing and impair memory.

(Shortform note: Research on soldiers undergoing survival training supports the idea that combat stress causes perceptual distortions and memory loss. In one study, soldiers who experienced the highest levels of stress during training were more likely to report perceptual distortions and memory loss. This suggests that the physiological changes caused by combat stress can have a significant impact on how people perceive and remember events.)

Mitigating Combat Stress: Training, Tactics, and Societal Support

Now, we will explain how to mitigate combat stress by examining internal strategies, then external systems and societal support.

Building the Resilient Warrior: Internal Strategies

Grossman and Christensen argue that mental preparation helps warriors handle the psychological impact of combat. They explain that if you believe that killing will traumatize you, it probably will. But if you rationalize and accept it in advance, then lawfully and legitimately applying lethal force needn't cause trauma or harm yourself. By getting ready to kill before the event, you decrease the chance of panicking, increase the likelihood of deterring your opponent, and reduce the possibility of killing inappropriately. You’ll be more ready to manage the consequences and less inclined to end your own life.

(Shortform note: Some psychologists disagree with the authors’ assertion that rationalizing killing in advance can prevent trauma and suicidality. In Perpetration-Induced Traumatic Stress, psychologist and pacifist Rachel MacNair argues that killing others is inherently traumatizing, even when it’s legal and rationalized in advance. She calls this “perpetration-induced traumatic stress,” a form of post-traumatic stress disorder that arises when people participate in killing or in actions they experience as taking life.)

Now, we will explain how internal conditioning assists warriors in managing stress and how tactical training improves resilience.

Internal Conditioning for Stress Management

Grossman and Christensen state that stress inoculation helps individuals adapt to new stressors. They describe a "stress resilience system" that enables you to improve your adaptability to new stressors. Developing resilience to pressure in a certain domain helps you adjust to different stressors.

(Shortform note: In Roadmap to Resilience, Donald Meichenbaum suggests that you can strengthen your resilience by creating a personal coping narrative. This involves writing down brief accounts of stressful events, focusing on the facts and how you coped with them. By regularly recording these experiences, you train your mind to store memories of stress in terms of coping and available resources rather than helplessness.)

They also introduce using controlled breathing as a method to manage stress and physiological responses. It's a simple method that can be applied in high-pressure moments to decrease your heart's beats per minute, reduce trembling, and create calmness and control. Tactical breathing lets you manage the sympathetic nervous system throughout a critical incident. Afterward, it helps separate your physical response from remembering the event.

Heart-Rate-Variability Biofeedback

Paul M. Lehrer and Richard Gevirtz have shown that heart-rate-variability biofeedback, which involves breathing at a specific pace, can help people regulate their autonomic nervous system. This technique works by strengthening the baroreflex, a mechanism that helps control blood pressure and heart rate. By enhancing this reflex, the technique can reduce sympathetic nervous system activity and increase parasympathetic activity, leading to better emotional regulation and stress management. This approach has been found effective in treating conditions like anxiety and posttraumatic stress disorder.

Tactical & Training Applications for Resilience

Grossman and Christensen assert that realistic training scenarios improve how you handle pressure. The more realistic the training, the more it prepares you for real-life situations. These training methods help you develop the right habits and responses and get used to the stress of battle, so you can perform better when it matters most.

(Shortform note: While realistic training scenarios can help you prepare for battle, they can also have negative effects. In The Body Keeps the Score, Bessel van der Kolk explains that when people are overwhelmed by inescapable terror, the brain’s alarm system imprints those experiences in rigid fear networks.)

Supporting Combatants: External Systems and Societal Support

Organizational and Institutional Support

Grossman and his co-author argue that organizational support is crucial for effective combat performance. They explain that a respected leader who demands effective action from their team is key. Having a comrade nearby also helps infantry soldiers to continue using their weapons. The authors add that historically, weapons operated by a team have accounted for most war casualties. This includes the chariot, the Greek phalanx, and the use of cannons. The phalanx, for example, was a dense formation of spear-wielding soldiers, highly trained to move as a coherent mass. Novices were positioned at the front, closely monitored and held accountable by experienced fighters at their backs.

(Shortform note: While organizational support can enhance combat performance, it can also have negative effects. In Achilles in Vietnam, Jonathan Shay argues that “moral injury” occurs when a soldier is compelled to act against their moral code. He explains that this can happen when a respected leader and a comrade nearby use the pressure of weapons operated by a team to push soldiers into violating their own moral code. Shay argues that moral injury is different from physical or psychological wounds because it leaves a lasting sense of betrayal and guilt. This can lead to long-term psychological distress, including depression, anxiety, and post-traumatic stress disorder.)

Cannons marked the initial organized military application of gunpowder. Cannons were lethal from the outset, unlike the initial muskets. Typically, they were operated by multiple people directly led by a sergeant or officer. Napoleon recognized how effective cannons were in battle and made sure his armies always had more of them than his foes. During the 1900s, the gun with an automatic mechanism took over the traditional position that the cannon held, operated by a group, as a weapon for mass killing. Crew-operated machine guns are still the main tools for inflicting casualties in battles at short distances, but group-enabling methods have evolved with the use of tanks and armored vehicles.

(Shortform note: The authors’ focus on the gun crew as the primary means of inflicting casualties at close range may be outdated. In Army of None, Paul Scharre argues that modern warfare increasingly disaggregates the act of killing, with the people who find, identify, and engage a target being physically separated. For example, armed drones and remote weapon stations allow operators to deliver lethal effects at close range while being hundreds or thousands of miles away. This means that the traditional concept of a gun crew physically present at the front lines may no longer be the primary means of inflicting casualties in close combat.)

Crew-operated armaments have been used in naval settings since the emergence of gunpowder. The contemporary notion of a military commander typically imagines an experienced warrior positioned behind troops, urging, motivating, disciplining, scolding, correcting, and rewarding them. This leadership style largely vanished with the fall of the Roman Empire but resurfaced with English longbowmen and the victorious forces during the age of gunpowder. The authors note that groups are a crucial additional factor. It was discovered that while only 15–20% of riflemen fired during World War II, crews operating crew-served weapons almost always did. Their reasons were mutual assistance, responsibility, and accountability. S.L.A. Marshall writes in his book, Men Against Fire, "I consider it a basic truth of combat that an infantry soldier's ability to persist with his weapons depends on whether he has—or thinks he has—a fellow soldier nearby."

Questioning the Data on Firing Rates

The authors’ claim that research “discovered” that individual riflemen in that war rarely fired their weapons, while team-served guns almost always did so because of group factors, is questionable. In 1988, historian Roger J. Spiller examined S.L.A. Marshall’s surviving field notes, interview materials, and personal papers. He found no underlying statistical compilations, tabulations, or methodological records to substantiate Marshall’s published numerical claims about combat firing behavior. Spiller concluded that these figures rest on impressionistic judgment rather than on demonstrable, documented research. Therefore, the assertion that only 15–20% of riflemen fired their weapons in that war should be treated as an unproven assertion rather than established fact.