UK serve 6 months deployed out of three years but still have PTSD problems

Longer Military Deployment Increases Risk of MH Problems
Aaron Levin
British troops start to show the psychological burdens of overseas deployments as time away from their home bases increases.

Americans often hear about the psychological demands on U.S. soldiers, whose tours of duty in Iraq have been extended from 12 to 15 months. They are not alone. New research shows that longer tours of duty appear to take their toll on troops from other countries too, according to an ongoing study of British forces by the King's Centre for Military Health Research at King's College London.

Operational tempo—the number and frequency of deployments—is a normal part of a military career, but rising demands for military operations may also increase stress on troops and their families. Commanders try to balance deployment with periods at home to allow troops to recover from the stresses of war and maintain family ties, with mixed success. The U.S. Senate in September rejected legislation requiring the Pentagon to allow troops a period at their home bases equal to time on deployments.

Military authorities in the United Kingdom have set "harmony guidelines" for how often and how long army troops can be deployed on operations—a six months' tour of duty followed by 24 months at home during any 36-month stretch. Thus a unit might be deployed for a maximum of 12 months out of three years.
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http://pn.psychiatryonline.org/cgi/content/full/42/20/16