The first prefix to be created was R which was used to identify Regular Army personnel who had re-enlisted after the close of World War I and the disbandment of the National Army. In 1920, a year after the close of World War I, the Army introduced the first 'service number prefix' which was intended to be a letter placed in front of the service number to provide additional information about the veteran. Throughout the remainder of World War I, service numbers were issued to most enlisted personnel with the numbers eventually ranging from 1 to 5 999 999. The first soldier to receive an Army service number during the First World War was Master Sergeant Arthur Crean who was designated to hold service number 1 in the National Army in February 1918. The Marine Corps and Coast Guard were also relatively small organizations without the need for a service number system to track personnel.

The decision to create Army service numbers was made in February 1918 with the first service numbers to be issued only to Army enlisted personnel the Army officer corps was still relatively small, and the Navy was still maintaining ship rosters to keep track of its personnel. As the strength of the National Army rose into the millions, this old method of musters and rosters became outdated and a new system had to be developed. Prior to this time, the only way to index lists of soldiers was by use of rosters and muster rolls. Service numbers (SNs) were first created in 1918 as a result of the United States Army becoming involved in World War I and the need for a record tracking system capable of indexing the millions of soldiers who were joining the ranks of the National Army. The first service number of the United States armed forces

Army enlisted record brief