Service number
Service number prefix and suffix codes were one and two letter designators written before or after a service number; a service member could only have one code at any given time. The purpose of these codes was to provide additional information regarding a military service member with the very first prefix codes created by the Army in 1920 and greatly expanded over the next thirty years. The Navy created the first suffix code "W", written after the service numbers of female enlisted personnel, but it was the Air Force that made the greatest use of suffix codes until 1965 when the Air Force switched to using prefixes. Some prefix and suffix codes were also re-introduced, with different meanings, by various branches of military. In the modern age, the only code that survives is the suffix code "FR", written after the social security numbers of Regular Air Force personnel.