 The 13th was charged with protection of the St. Mihiel sector, and its pilots soon were active in intercepting and attacking enemy aircraft that attempted reconnaissance over Allied lines.The Spads also escorted Allied observation planes deep into enemy territory where their pilots sometimes engaged enemy planes and attacked hostile balloons.While participating in the St. Mihiel Offensive, which was undertaken to eliminate the salient in the front lines around St. Mihiel that had existed since early in the war, the 13th fought with vigor.