From June 1945 until July 1946, reconnaissance and security along the border between the U.S. and Soviet zones of occupation in Germany in the area north and south of Fulda was the mission of elements of the U.S. 3rd and 1st Infantry Divisions. By July 1946, the 1st, 3rd, and 14th Constabulary Regiments (arranged from north to south) had assumed responsibility for inter-zonal border security in an area to include that which later become famous as the Cold War Fulda Gap. The U.S. Constabulary as a headquarters was subsequently drawn down, but individual constabulary regiments were retitled "armored cavalry regiments". This coincided with the 1951 upgrade of the U.S. Army's mostly administrative and occupation responsibilities in Germany to a combat army via the arrival of four combat divisions from the United States. Thus, from 1951. until 1972, the 14th Armored Cavalry Regiment (ACR) patrolled the Fulda Gap. After the return of the 11th Armored Cavalry Regiment from Vietnam in 1972, the 11th ACR relieved the 14th ACR and took over the reconnaissance mission in the Fulda Gap until the end of the Cold War.