A computer-implemented method for differentiating friendly and enemy units in a soldier's head-mounted display and warning a soldier when an enemy unit gains line-of-sight access to his or her position. The method includes a Unit Identifier (100) for associating units in aerial imagery with soldiers on the battlefield, a Commander Presenter (102) for presenting the aerial imagery and unit positions to a commander, a Unit Annotator (104) for enabling commanders to identify unknown units, and a Soldier Presenter (106) for identifying units that appear in a soldier's head-mounted display.