Combat stress reaction (CSR), is emotional or physical tension, strain, or distress resulting from exposure to combat and combat-related conditions.. Also known as "combat fatigue", it has some overlap with the diagnosis of acute stress reaction used in civilian psychiatry. Historically, it has some link to shell shock, and can sometimes precursor post-traumatic stress disorder.
Combat stress reaction is an acute reaction including a range of behaviours resulting from the stress of battle which decrease the combatant's fighting efficiency. The most common symptoms are fatigue, slower reaction times, indecision, disconnection from one's surroundings, and inability to prioritize. Combat stress reaction is generally short-term and should not be confused with acute stress disorder, post-traumatic stress disorder, or other long-term disorders attributable to combat stress, although any of these may commence as a combat stress reaction.
The ratio of stress casualties to battle casualties varies with the intensity of the fighting, but with intense fighting it can be as high as 1:1. In low-level conflicts it can drop to 1:10 (or less).
In World War I, shell shock was considered a psychiatric illness resulting from injury to the nerves during combat. The horrors of trench warfare meant that about 10% of the fighting soldiers were killed (compared to 4.5% during World War II) and the total proportion of troops who became casualties (killed or wounded) was 56%.
Whether a shell-shock sufferer was considered "wounded" or "sick" depended on the circumstances. The large proportion of World War I veterans in the European population meant that the symptoms were common to the culture.

Signs and symptoms

Combat stress reaction symptoms align with the symptoms also found in psychological trauma, which is closely related to post-traumatic stress disorder (PTSD). CSR differs from PTSD (among other things) in that a PTSD diagnosis requires a duration of symptoms over one month, which CSR does not.
Fatigue related symptoms
The most common stress reactions include:
The slowing of reaction time
Slowness of thought
Difficulty prioritising tasks
Difficulty initiating routine tasks           
Preoccupation with minor issues and familiar tasks
Indecision and lack of concentration
Loss of initiative with fatigue


In the military, therapy starts with prevention by training and providing good morale and support. Simple procedures like providing adequate rest, food and shelter are important. Relaxation exercises have a role as does critical event debriefing.
Once a service member has deteriorated beyond this they are usually relieved of duty and given support, dry clothes, food and rest. When appropriate they are given supportive counselling aimed at their speedy recovery. Some are prescribed psychotropic medications and simply discharged.