The 12th Port of Embarkation, later designated 377th Theater Sustainment Command, was constituted on 2 July 1942 and was activated 5 July 1942 at Fort Dix, New Jersey. The unit was converted, reorganized, and redesignated 7 November 1942 as the 12th Port. The unit was inactivated 4 January 1946 at Camp Kilmer, New Jersey and later redesignated 3 November 1948 in New Orleans, Louisiana, as the 377th Transportation Major Port. On 11 September 1950 the 377th was called to Camp Kilmer, New Jersey. Later, the unit moved to Fort Eustis, Virginia and stayed on active Federal Service until 10 October 1952. From 1953 until 1963, the 377th remained in a Reserve status and experienced several changes in unit designation.

The United States Army Reserve (USAR) is a reserve force of the United States Army. Together, the Army Reserve and the Army National Guard constitute the Army element of the reserve components of the United States Armed Forces.