The military is a group of individuals who are usually trained and equipped to perform national security tasks in unique and often chaotic and trauma-filled situations. These situations can include the front-lines of battle, national emergencies, allied assistance, or the disaster response scenarios where they are providing relief-aid for the host populations of both friendly and enemy states. Though many psychologists may have a general understanding with regards to a humans response to traumatic situations, military psychologists are uniquely trained and experienced specialists in applied science and practice among this special population. While the soldiers may be providing direct aid to the victims of events, military psychologists are providing specialized aid to both soldiers, their families, and the victims of military operations as they cope with the often "normal" response or reaction to uncommon and abnormal circumstances.
In addition to the specialized roles previously mentioned, military psychologists often study the dynamics, train people in, and consult on hostage negotiations. In some cases the psychologists might not be the one directly handling the hostage situation, but hostage negotiators find value in resolving the hostage crisis using many of the scientific principles that are derived from the science of psychology. In addition, many of the principles of the scientific discipline of clinical psychology have their roots in the work of the early military psychologists of World War II.
Another common practice domain for military psychologists is in performing fitness for duty evaluations, especially in high risk and high reliability occupations. The set of unique challenges often faced by those in the military and the professions of arms such as: police, strategic security, and protective services personnel, the ability to perform reliable and accurate fitness for duty evaluations adds value and maximizes the human capital investment in the workplace by optimizing retention of the talents of active and prospective service men and women while minimizing risk in many areas including violence, mishap, and injury potential. The types of fitness evaluations include both basic entry examinations and career progression examinations such as those conducted when individuals are seeking promotion, higher-classification clearance status, and specialized, hazardous, and mission critical working conditions. When operational commanders become concerned about the impact of continuous, critical, and traumatic operations on those in their command, they often consult with a military psychologist. Military psychologists can assess, diagnose, treat and recommend the duty status most suitable for the optimal well-being of the individual, group, and organization. Events that affect the mental state, resilience or psychological assets and vulnerabilities of the warrior and the command are where military psychologists are most equipped to meet the unique challenges and provide expert care and consultation to preserve the behavioural health of the fighting force. The fitness evaluations might lead to command directed administrative actions or provide the information necessary to make decisions by a medical board or other tribunal and must be thoroughly conducted by non-biased individuals with the experience and training necessary to render a professional opinion that is critical to key decision makers. Military psychologists must be well versed in the art and science of psychology as specialized applied practice professionals. They must also be highly competent generalists in the military profession, and be able to understand both professions well enough to examine human behavior in the context of military operations. It takes the psychologist several years beyond the doctorate to develop the expertise necessary to understand how to integrate psychology with the complex needs of the military.
Another very select and infrequent use of military psychology is in the interview of subjects, the interrogation of prisoners, and the vetting of those who may provide information of operational or intelligence value that would enhance outcomes of friendly military operations or reduce friendly and enemy casualties. Psychology's scientific principles applied here allow the interviewer, agent, or interrogator to get as much information as possible through non-invasive means without the need to resort to active measures or risk violating the rules of engagement, host nation agreements, international and military law or crossing the threshold of the Geneva Conventions' guidelines to which the United States and its allies subscribe, regardless of the status of many of the modern belligerent countries on the international laws and United Nations agreements.