After 27 months of serving in the army, Middleton got his first promotion, to corporal. Promotions came very slowly, and occurred only when a position was vacated by someone else getting promoted or retiring. Shortly after his promotion on 10 June 1912, Corporal Middleton was transferred to Fort Leavenworth, Kansas, where he would have a chance to compete for an army commission. Here Middleton attended an intensive training course to prepare for the written examination required for a second lieutenant's commission. Of the 300 civilians and enlisted men who took the exam, 56 of them passed and were commissioned. Middleton's score was just about in the middle of the passing scores. Almost all of those passing were college graduates, coming from schools such as Harvard, Yale, Virginia Military Institute, and Stanford. Four of the 56, including Middleton, would go on to become general officers.