From December 1943, through the end of World War II, Milburn commanded the XXI Corps (United States).

Milburn's XXI Corps played a decisive role in collapsing the Colmar Pocket in February 1945.

[1] In his The History of the French First Army, General Jean de Lattre de Tassigny described General Milburn in this manner: When I saw Maj.-Gen. Frank W. Milburn arrive at Rothau at 10.00 on the 25th January, lean and muscular and straight of eye, with the energetic features of a fighter, it did not take me long to know that I would find in him the most careful and loyal of subordinates.

The steadfastness of his character, his clear view of realities and his leader-like authority, were apparent to me at once, and I felt that I could have complete confidence in him to bring to a successful conclusion the rough task which was going to fall to his U.S. 21st Army Corps.

Subsequently, Milburn served briefly as the acting commander for the Seventh Army and then the XXIII Corps.