The 337th Infantry did not participate in any named campaigns; instead the regiment provided individual replacement soldiers for divisions engaged in combat.

[5][6][7] After completing its war service in France, it arrived at the port of New York aboard S.S. Leviathan on April 2, 1919.

[11] The regiment was ordered into active military service 15 May 1942 and reorganized at Camp Shelby, Mississippi, using a cadre provided by the 2nd Infantry Division.

In July 1943, the regiment was organized with 3,256 officers and enlisted men:[13] It departed Hampton Roads Port of Embarkation aboard HMS Andes on 24 December 1943, landed in Casablanca, French Morocco, on 2 January 1944 and received amphibious warfare training at Port aux Poules.

It saw heavy combat attacking the German's Gustav and Gothic Lines as they moved north up the Italian Peninsula during Operation Diadem.

The regiment initially held defensive positions north of the Garigliano River until it attacked and seized Castellonorato until it was stopped by German resistance south of Monte Campese on 16 May 1944.

On 1 October, Sergeant Chris Carr of Company L earned the Medal of Honor for actions near Guignola, Italy.

On 26 April the division crossed the Adige River in the Verona area and by 1 May was clearing the Piave Valley.

The regiment departed Fagianeria, Italy for Hampton Roads and was inactivated at Camp Patrick Henry, Virginia, on 25 August 1945.

As part of Operation Bold Shift, the battalion changed their missions to better train Army Reserve and National Guard units.

The 3rd Battalion is an Army Reserve unit assigned to the 4th Cavalry Brigade at Fort Knox, Kentucky and provides Observer, Controller/ Trainers (OC/T) and Staff to various Mobilization Training Centers responsible for conducting post mobilization training to Reserve Component units preparing them for deployment to Overseas Contingency Operations.