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.
2nd Battalion, 6th Marines 2nd Battalion, 6th Marines (2/6) is an infantry battalion in the United States Marine Corps based out of Camp Lejeune, North Carolina. Also known as "The Ready Battalion" or "2/6 Spartans", it consists of approximately 800 Marines and Sailors and falls under the command of the 6th Marine Regiment and the 2nd Marine Division.