Military psychology is a broad market of psychology in which virtually any and all subfields of psychology where the lessons of personality, organizational and abnormal psychology among others are applied to the needs or desires of military planners and strategists. Reasons for their application may be immediate or sustained. The application of psychological research or theory to the military can be used to analyze either enemy or friendly forces, exemplified by perfecting an attack on an enemy or strengthening the weakness of an ally. By extension, military psychology could be used to examine the differences in attitude to the battlefield in terms of philosophy and execution of operations. The field has developed its greatest recognition through the variably sustained or ineffective post-combat programs for troubled veterans. Conditions like "shell shock" and "post-traumatic stress disorder" (PTSD) have figured prominently in the development of military therapy programs. Strategically, intelligence and personality testing have been applied to placement exams for prospective military recruits.
The events of World War I had a formative effect on the application of psychology to the realities of the battlefield, giving the nascent field crucial legitimacy. Co-founder of the British Psychological Society and the National Institute of Industrial Psychology, Dr. Charles Myers, was selected as the primary advisor on psychological matters to the British armies in France during the war. His work is considered foundational and he himself describes in statements that it was a frustrating endeavor to have British military elite recognize the legitimacy of his claims that soldiers deserved psychological consideration for their inability and perceived unwillingness to perform in battle. Coining the term "shell shock," he engraved an enduring term into historical consciousness that defines the apparent psychological damage inflicted by war. The term today