A study of 5,547 soldiers has found that those who had been deployed for 13 months or more within the last three years were 1.55 times more likely to suffer from post-traumatic stress disorder (PTSD) than soldiers who had had shorter deployments. Those who had seen more active service and more combat were also more likely to have poorer physical health and severe alcohol problems. The number of deployments was less important in causing mental health problems than the length of the deployments and PTSD was also associated with soldiers expecting to be deployed for a certain length of time only to find that they were asked to serve for much longer.
Rona, Roberta J. ... [et al] - Mental health consequences of overstretch in the UK armed forces : first phase of a cohort study British Medical Journal 22nd September 2007, 603-606