There have been a number of 18th Divisions in the history of the United States Army:
The first 18th Division was originally a National Guard division established in early 1917 consisting of troops from Arkansas, Louisiana, and Mississippi. By the end of that same year, the 18th Division had been redesignated the 39th Division (later the 39th Infantry Division).
Division commander: Colonel James H. Frier (interim), August 21, 1918-September 15, 1918; Brigadier General George H. Estes, September 16, 1918-October 14, 1918; Colonel James H. Frier (interim), October 14, 1918-October 23, 1918; Brigadier General Frederick B. Shaw, October 24, 1919-October 26, 1918; Brigadier General George H. Estes, October 27, 1919-February 14, 1919.
Commander, 35th Infantry Brigade: Colonel Robert C. Williams (interim), August 25, 1918-September 16, 1918; Brigadier General George H. Estes, September 16, 1918-October 13, 1918; Colonel Josephus S. Cecil, October 14, 1918-October 26, 1918; Brigadier General George H. Estes, October 27, 1918-February 14, 1919.
Commander, 36th Infantry Brigade: Colonel James H. Frier (interim), August 21, 1918-October 23, 1918; Brigadier General Frederick B. Shaw (October 24, 1918-February 6, 1919; Colonel James H. Frier, February 7, 1919-February 14, 1919.