The 46th Infantry was constituted in the Regular Army 15 May 1917, organized 4 June 1917 at Fort Benjamin Harrison, Indiana and assigned to the 9th Division 5 July 1918. Relieved from assignment to the 9th Division 15 February 1919 and inactivated 16 November 1921 at Camp Travis, Texas. Disbanded 31 July 1922. Reconstituted in the Regular Army 28 August 1941 as 46th Infantry (Armored) and assigned to the 5th Armored Division 28 August 1941. Activated 1 October 1941 at Fort Knox, Kentucky. Redesignated 46th Armored Infantry 1 January 1942. Regiment broken up 20 September 1943 and its elements reorganized and redesignated as follows: Regimental Headquarters and 3d Battalion, 46th Armored Infantry redesignated 46th Armored Infantry Battalion; 1st Battalion, 46th Armored Infantry redesignated 47th Armored Infantry Battalion and 2d Battalion, 46th Armored Infantry redesignated 15th Armored Infantry Battalion. Battalions inactivated 8-13 October 1945 at Camp Myles Standish, Massachusetts. Activated 6 July 1948 at Camp Chaffee, Arkansas. Inactivated 1 February 1950 at Camp Chaffee. Activated 1 September 1950 at Camp Chaffee. Inactivated 16 March 1956 at Camp Chaffee. Relieved from assignment to the 5th Armored Division 15 February 1957. 46th, 47th and 15th Armored Infantry Battalions consolidated 1 July 1959 to form the 46th Infantry, a parent regiment under the Combat Arms Regimental System. Elements served with the 198th Light Infantry Brigade and, later, 23d Infantry Division ("Americal") in Vietnam (1st Battalion, 46th Infantry 22 October 1967 - 20 June 1972 and 5th Battalion, 46th Infantry 31 March 1968 - 21 May 1971).
Decorations: The 47th Armored Infantry Battalion (formerly 1st Battalion, 46th Armored Infantry) was awarded the Presidential Unit Citation for action in the Huertgen Forest during World War II. The 46th, 47th and 15th Armored Infantry Battalions were awarded the Luxembourg Croix de Guerre (streamer embroidered "Luxembourg") for action in Luxembourg during World War II. 1st Battalion, 46th Infantry was awarded the Valorous Unit Award for action in Quang Tin Province, Repubic of Vietnam.
Campaign Credits: World War II: five campaign credits (Normandy, Northern France, Rhineland, Ardennes-Alsace and Central Europe).
Vietnam: thirteen campaign credits (Counteroffensive Phase III, Tet Counteroffensive, Counteroffensive Phase IV, Counteroffensive Phase V, Counteroffensive Phase VI, Tet '69 Counteroffensive, Summer-Fall 1969, Winter-Spring 1970, Sanctuary Counteroffensive, Counteroffensive Phase VII, Consolidation Phase I, Consolidation Phase II and Cease-fire)