ABSTRACT Introduction Over the past two decades, overseas deployments of the French Army have been characterized by the exposure of its service personnel to sustained, high levels of combat stress. There is a need to assess their mental health throughout the deployment cycle, identify risk factors associated with stress-related disorders, and characterize the factors that promote long-term well-being. Methods We conducted two pilot studies within four units of the French Army: a conventional combat unit, a counterterrorist unit, a combat service support unit, and a medical support unit. Study 1 (n = 65) analyzed the psychological functioning of service personnel with respect to their personality and stress management characteristics. Study 2 (n = 40) analyzed the impact of overseas deployment on stress-related psychological outcomes. Results Overall, results from study 1 showed that service personnel have a protective psychological functioning, which is particularly developed in the counterterrorist unit. In study 2, although no stress-related disorder symptoms were observed with the psychometric tools used, a certain degree of psychological dysfunction (social dysfunction and lower positive affect) was detected post-deployment. Conclusions These two complementary studies are key elements in developing a better understanding of unmet, medico-military needs that lie on the pathway that links exposure to stressors to impaired health. Certain personnel enrolled in the French Army (notably, the counterterrorist unit) were found to have a high level of protective psychological functioning, largely due to the training they receive. Nevertheless, overall, overseas deployment was associated with poorer psychological functioning and the emergence of social dysfunction, especially in units responsible for the care of service personnel (medical support and combat service support units).