Interior view of a bombed-out church: many soldiers lay on stretchers on the floor; other soldiers move about, some tend the wounded; gaping holes in the walls of the church; a large painting hangs over alter; a small dog stands among the rubble. U.S. Signal Corps photo, 1918. During combat or training operations, military units may establish aid stations behind front lines to provide medical support to troops in the field. In United States military operations, these are most commonly referred to as Battalion Aid Stations; in Commonwealth countries, Regimental Aid Posts.