The US Fifteenth Army was the last field army to see service in northwest Europe during World War II. It was first activated in early 1945, with Lieutenant General Leonard Gerow assuming command on 15 January. Fifteenth Army never entered the main line of battle. However, its formations did see some action, when it contained and then reduced the enormous Ruhr pocket from the west during April 1945 in conjunction with elements of Ninth Army. Gerow remained in command of Fifteenth Army until November 1945.