The 503rd Infantry Regiment and the 2nd Infantry Division are both formations of what military branch
2nd Infantry Division (United States) The 2nd Infantry Division ("Indianhead"; "2ID," "2nd ID", or "Second D") is a formation of the United States Army. Its current primary mission is the defense of South Korea in the initial stages of an invasion from North Korea until other American units can arrive. There are approximately 17,000 soldiers in the 2nd Infantry Division, with 10,000 of them stationed in South Korea, accounting for about 35% of the United States Forces Korea personnel.
144th Infantry Regiment (United States) The 144th Infantry Regiment is an infantry regiment of the United States Army, Texas Army National Guard. It was formed in 1880 and served in several American wars including the present War on Terror. Currently, only the 3rd Battalion remains, and it is a part of the 56th Infantry Brigade Combat Team of the 36th Infantry Division.