The '''Signals Intelligence Service (SIS)''' was the Army's codebreaking division headquartered at [[Arlington Hall]]. It was a part of the Signal Corps so secret that outside the office of the Chief Signal officer, it did not officially exist. | The '''Signals Intelligence Service (SIS)''' was the Army's codebreaking division headquartered at [[Arlington Hall]]. It was a part of the Signal Corps so secret that outside the office of the Chief Signal officer, it did not officially exist. |