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 Guards Reserve Division (German Empire) The 2nd Guards Reserve Division ("2. Garde-Reserve-Division") was a reserve infantry division of the Imperial German Army in World War I. Despite its name, it was not a reserve formation of the Prussian Guards like the 1st Guards Reserve Division. Instead, other than the 55th Reserve Infantry Regiment, which was raised by the 4th Guards Grenadiers, it was primarily made up of non-Guards reservists from Westphalia and Hanover. It was formed on mobilization in August 1914 as part of X Reserve Corps and dissolved in 1919 during the demobilization of the German Army after the Armistice.