[48] In an event memorialized in battery lore as "The Battle of Who Run", his soldiers began to flee during a sudden night attack by the Germans in the Vosges Mountains; Truman succeeded at ordering his men to stay and fight, using profanity from his railroad days. The men were so surprised to hear Truman use such language that they immediately obeyed.[35]
Truman's unit joined in a massive prearranged assault barrage on September 26, 1918, at the opening of the Meuse–Argonne offensive.[49] They advanced with difficulty over pitted terrain to follow the infantry, and set up an observation post west of Cheppy.[49] On September 27, Truman saw through his binoculars an enemy artillery battery deploying across a river in a position which would allow them to fire upon the neighboring 28th Division.[49] Truman's orders limited him to targets facing the 35th Division, but he ignored this and patiently waited until the Germans had walked their horses well away from their guns, ensuring they could not relocate out of range of Truman's battery.[49] He then ordered his men to open fire, and their attack destroyed the enemy battery.