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.
Functional brigade A functional brigade —or functional support brigade— is a brigade specialized in combat support or combat service support for a particular military role. The primary purpose of a functional brigade is to plug into operational formations at the theater level or those commanded by corps or division commanders performing as the Army Service Component Command (ASCC) once deployed, and to conduct operational or theater level tasks or support. Functional brigades, like modular support brigades, have a modular subordinate structure that may vary considerably among brigades of the same type. Unlike the modular support brigades, functional brigades typically operate under theater control and depend on theater-level elements for signal and other support. The theater force may task-organize them to corps or division headquarters. Types of functional brigades include: