At the Battle of Missionary Ridge on November 25, 1863, during the Chattanooga Campaign, the 18-year-old MacArthur inspired his regiment during a largely uncoordinated and spontaneous frontal assault of Union forces against entrenched Confederate forces on a hilltop. During the charge the regimental flags were carried in front, so that every flag-bearer was constantly a target, causing immense casualty among them. MacArthur seized the flag from a fallen comrade and planted the regimental flag on the crest of Missionary Ridge at a particularly critical moment, shouting ""On Wisconsin."" For these actions, he was awarded the Medal of Honor. He was brevetted colonel in the Union Army the following year. Only 19 years old at the time, he became nationally recognized as "The Boy Colonel" (not to be confused with Henry K. Burgwyn, known as the ""Boy Colonel of the Confederacy"").