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Combat and Operational Stress Reactions (COSRs)

Combat and operational stress reactions (COSRs) are defined as "physical, emotional, cognitive, or behavioral reactions, adverse consequences, or psychological injuries of service members who have been exposed to stressful or traumatic events in combat or military operations," according to DOD Instruction 6490.05. COSRs can vary in severity depending on a variety of operational conditions, including intensity, duration, frequency of combat exposure, leadership, and unit morale, among other things. COSRs, however, do not represent mental health disorders or medically diagnosable conditions and concerns.

The term 'combat and operational stress reaction' is used to describe two different types of military stress reactions: acute stress reactions in the combat environment called combat stress reactions (CSRs), and reactions to more sustained military operational stressors, or operational stress reactions (OSRs).

Combat Stress Reactions

CSRs occur in combat or preparation for combat. They are hard-wired survival responses that encompass physiological, behavioral, emotional, mental, and other changes in body processes. Life threatening situations trigger the autonomic nervous system, which is regulated by two opposing divisions — the sympathetic nervous system, responsible for arousal, and the parasympathetic nervous system, responsible for shutdown. The result is a continuum of automatic responses referred to as the 'defense cascade,' characterized by extreme (but relatively brief) highs or lows in physiological functions, such as awareness/arousal, behavioral, emotional, mental, speech, and sensorimotor. These changes are intense and cause moderate to severe impairment while they last, but their duration is only hours or, at most, a few days.

Examples of combat stressors include:

  • Personal injury
  • Killing of combatants
  • Witnessing the death of an individual
  • Death of another unit member
  • Injury resulting in the loss of a limb

Some of the combat stress reactions a service member may experience include restlessness, panic, irritability, rage, confusion, memory problems, fatigue, insomnia, palpitations, shortness of breath, and dissociation.

The clinical signs and symptoms profiles associated with combat stress reactions are provided in this one-page overview.

Operational Stress Reactions

OSRs are expected temporary behavioral, cognitive, emotional, and physical changes resulting from the experiences or consequences of repeated exposure to a single stressor, or multiple stressors, in combat or non-combat operational settings. Examples of operational stressors include:

  • Difficult living and working environment (e.g., isolation, extreme climates/surroundings, or sensory stressors)
  • Experiencing or witnessing harassment, bullying, or work-related interpersonal conflict
  • High workload (e.g., long work hours and high task demands)
  • Repeated exposure to trauma, danger, and loss
  • Sleep disrupting work conditions (e.g., shift work, overnight work)
  • Stressful events involving loved ones or friends (e.g., marital problems, illness, or death)

Some of the operational stress reactions a service member may experience include anxiety or fear; attention, concentration, or memory deficits; burnout, emotional exhaustion, or being disengaged; depressed mood, sadness, helplessness, or grief; difficulty falling or staying asleep; frustration, irritability, or anger; and PTSD symptoms.

The most common stressors and associated indicators that are indicative of operational stress reactions are provided in this one-page overview.


Because COSRs are expected responses to combat and military operations, the services maintain combat and operational stress control (COSC) programs to improve service members' ability to manage combat and operational stress. The primary objectives of COSC programs are to:

  • help service members recognize signs and symptoms of COSRs
  • prevent them through training to increase confidence and skills
  • decrease the impact of combat and operational stress with simple measures, such as reassurance, rest, and ensuring safety

If service members with COSRs do not respond to initial interventions, referral to a licensed mental health provider is recommended.

PHCoE’s Combat Stress Reactions: Tips for Providers offers an overview of the 'defense cascade' described above, examples of service members' experiences, and tips for working with service members who may experience CSRs.

Similarly, PHCoE's Operational Stress Reactions: Tips for Providers offers an overview of the most common operational stressors and associated indicators; and provides guidance on assessing, intervening, and planning for potential upcoming OSRs.


PHCoE developed joint service training, Combat and Operational Stress 101, to encourage service members' total fitness by optimizing physical, mental, and emotional wellbeing. The training was developed in conjunction with the services to support the COSC mission. These training decks can be used by all services to train their members in COSC practices:

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