I can't find the link right now, but I remember reading a study (also funded by the military) about using sleep masks with ear plugs to improve the quality of soldier's sleep when they do have the opportunity of sleeping. Deployed soldiers frequently don't have the luxury of a regular sleep schedule. This study, combined with the other one, seems to be an effort to deal with the problems of sleep deprivation. Soldiers can get relatively good quality sleep when they can, and be alert when they must.