Following the war, McLain returned to his banking career but remained in the National Guard, and in June 1937, he was promoted to brigadier general. In the next year, he completed an abbreviated course at the Command and General Staff School. He was mobilized with the National Guard 45th Infantry Division in September 1940 and commanded its artillery. During the invasion of Sicily, he attracted the attention of Lieutenant General Omar Bradley. McLain then fought with the 45th in Italy, including at the Anzio landing. Bradley arranged his transfer in April 1944 and sent him to Normandy in charge of the 30th Infantry Division. In late July, Bradley gave McLain command of the 90th Infantry, rated a "problem" division. He was promoted to major general the next month.
McLain was the 90th's third commander in three months. Both of his predecessors had been mediocre leaders, and battlefield challenges in Normandy were extraordinarily severe. Leading by example with an understated command style, McLain and his assistant, Brigadier General William G. Weaver, transformed the 90th into one of the best divisions in Lieutenant General George S. Patton's Third Army. In October, McLain took over XIX Corps, partly because he had earned the advancement and partly because the army found it politically expedient to recognize an outstanding National Guardsman. He was the first American citizen-soldier to command a combat corps since the Civil War.
Despite his civilian background, McLain earned the respect of his regular army subordinates. His corps spent the remainder of the war in Lieutenant General William H. Simpson's Ninth Army. In March 1945, XIX Corps spearheaded the northern pincer in the encirclement of the Ruhr, and in April, it led Ninth Army's push to the Elbe. Had a further thrust to Berlin been ordered, he believed that his corps could have reached the city in six days. McLain won promotion to lieutenant general in June 1945.
He remained in the army after the war, serving as its chief of information (1946–1949) and as comptroller of the army (1949–1952). He retired in March 1952. McLain died in Washington, D.C., on 14 December 1954.
Richard G. Stone
Bradley, Omar N. A Soldier's Story. New York: Henry Holt, 1951.; Colby, John, et al. War from the Ground Up: The 90th Division in World War II. Austin, TX: Nortex Press, 1951.; Ryan, Cornelius. The Last Battle. New York: Simon and Schuster, 1966.; Whitlock, Flint. The Rock of Anzio: From Sicily to Dachau: A History of the 45th Infantry Division. Boulder, CO: Westview Press, 1998.