The Signal Intelligence Service (SIS) was the United States Army codebreaking division through World War II. It was founded in 1930 to compile codes for the Army. It was renamed the Signal Security Agency in 1943, and in September 1945, became the Army Security Agency. For most of the war it was headquartered at Arlington Hall, on Arlington Boulevard in Arlington, Virginia, across the Potomac River from Washington (D.C.). During World War II, it became known as the Army Security Agency, and its resources were reassigned to the newly established National Security Agency (NSA).

Arlington Hall is a historic building in Arlington, Virginia, originally a girls' school and later the headquarters of the United States Army's Signal Intelligence Service (SIS) cryptography effort during World War II. The site presently houses the George P. Shultz National Foreign Affairs Training Center, and the Army National Guard's Herbert R. Temple Jr. Readiness Center. It is located on Arlington Boulevard between S. Glebe Road and S. George Mason Drive.