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.
31st Infantry Division (United States) The 31st Infantry Division was a unit of the Army National Guard in World War I and World War II. It was originally activated as the 10th, a division established in early 1917 consisting of Alabama, Florida, and Georgia national guardsmen. By the end of that same year, the 10th Division became the 31st. In World War II, national guardsmen from Mississippi were included in the division.