I had a discussion recently about American military women in combat. It was triggered by an article on Jezebel, Don’t Put Women in Combat, Says Female Combat Veteran. Women in the US military are not allowed to do certain things, like join the special forces (there is no G. I. Jane navy seal), or serve as enlisted on submarines, or be part of combat units.
On submarines, for example, the restriction is justified by space limitations. They are not built to accomodate two groups living and showering separately, and rebuilding would cost too much -- obviously, the sci-fi no-brainer unisex solution is just a fantasy -- however; just recently, women were allowed to serve as officers on submarines. I presume this is because officers have private quarters.