New regulations declared that on all but the most official of documents (such as a DD Form 214 or evaluation reports) social security numbers would only list the last four digits.
The reason for this was to prevent possible identity theft issues committed by service members who had received a bad evaluation or who were disgruntled with their commanding officer.
The entire range of United States service numbers extends from 1 to 99,999,999 with the United States Army and Air Force the only services to use numbers higher than ten million.
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.