A service number is an identification code used to identify a person within a large group. Service numbers are most often associated with the military; however, they may be used in civilian organizations as well. National identification numbers may be seen as types of service numbers. The term "serial number" is often seen as a synonym of service number; however, a serial number more accurately describes manufacture and product codes, rather than personnel identification. In the Canadian military, a "serial number" referred to a unique number assigned each unit that mobilized for the Second World War. Australia In the First Australian Imperial Force soldiers were allotted numbers known as regimental numbers. These were allotted to NCOs and other ranks but not to officers or nurses, who had no numbers. Regimental numbers were rarely unique. Each battalion or corps had its own sequence, usually starting at 1, although some units were formed in the field and this did not occur. The result was that several dozen soldiers had the prestigious number 1, which was usually given to the Regimental Sergeant Major or the Regimental Quartermaster Sergeant. When soldiers were transferred from one unit to another, they often kept their number if it was not already held by someone else. Otherwise, they might be allotted a new number or the letter A or B might be added to make the number unique with their unit again. Re-enlisted soldiers often used the additional letter R. In 1917, the AIF switched to a scheme whereby reinforcements were drawn from the common pool instead of being supplied on a per-unit or corps basis. These were known as "general reinforcements" and they were allotted unique numbers in the range of 50000–80000. Despite the limitations of the scheme, in researching a soldier, it is handy to know the regimental number. In 1921, the assignment of identifying numbers based on regiments was abolished in the Australian Army and replaced with an Army-wide system. This meant that soldiers in all branches of the Army received a unique number, and if they re-enlisted they kept their previously allocated number. The problems inherent in the First World War scheme were acknowledged and all members of the Second Australian Imperial Force were allocated a unique service number known as an Army number. The first letter represented the state of enlistment: N: New South Wales; V: Victoria; Q: Queensland; S: South Australia; W: