The regiment didn't participate in any named campaigns during the war; its Infantrymen were used as individual replacements to the fighting Divisions.

[8][9] Pursuant to the National Defense Act of 1920, the 338th Infantry was reconstituted in the Organized Reserve on 24 June 1921, assigned to the 85th Division, and allotted to the Sixth Corps Area.

The primary ROTC "feeder" school was Michigan State College of Agriculture and Applied Science in Lansing.

[10] The 338th Infantry was ordered into active military service 15 May 1942 and reorganized at Camp Shelby, Mississippi.

In July 1943, the regiment was organized with 3,256 officers and enlisted men:[11] The regiment departed Hampton Roads Port of Embarkation in December 1943 aboard the USS General William A. Mann[12][13] with its supporting 329th Field Artillery Battalion.

After service in the Mediterranean Theater it was disbanded 25 August 1945 at Camp Patrick Henry, Virginia.