After his assignment to IV Corps, Vann was assigned as the senior American advisor in II Corps Military Region in the early 1970s when American involvement in the war was winding down and troops were being withdrawn. For that reason, his new job put him in charge of all United States personnel in his region, where he advised the ARVN (Army of the Republic of Vietnam) commander to the region and became the first American civilian to command U.S. regular troops in combat. His position was the equivalent in responsibilities of a major general in the US Army.