When the call went out for recruits to fight in Europe, Johnson dropped out of flight school and enlisted in the Texas National Guard on August 10, 1917.

Johnson was sent to Camp Bowie in Fort Worth, Texas, on August 23, 1917, where he was made a Sergeant on September 7, 1917, with Company E, 141st Infantry, 36th Division.

Johnson traveled with the officers of Company E, 141st Infantry Regiment on the USS Finland, embarking on July 26, 1918, from Hoboken, New Jersey.

After moving into support positions in September, it was assigned to prepare to relieve the 2d U. S. Division in the Épernay-Chalons region.

[3] On October 8, 1918, the regiment began participation in one of the great chapters in its combat history, the Meuse-Argonne campaign.

On that day, along a line extending four kilometers east to west, the 141st and 142d regiments attacked German positions, resulting in a "substantial gain of ground" but suffering casualties to sixty-six officers and 1,227 enlisted men.

In January 1921 he was promoted to captain in the 56th Cavalry Brigade, Texas National Guard, and worked as an oil salesman for Gulf.

In 1944 he was promoted to major general and made commander of the all-black 2nd Cavalry Division, which was dismounted and performed various service and support functions in the North African Campaign from February, 1943 to May, 1944.

From August 1944 to September 1945 he was made commander of the all-black 93rd Infantry Division which performed service and support tasks in the New Guinea-Philippines Campaign.