Service number

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.

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.

[1] In 1921, the assignment of identifying numbers based on regiments was abolished in the Australian Army and replaced with an Army-wide system.

A dual system existed until July 1947 as existing personnel kept their Second AIF numbers until that point, while new enlistments received a service number starting from X500000, while maintaining the state-based prefix of the old Second AIF system.

The use of the SIN was granted by Revenue Canada to the CF for service numbers as a temporary measure and was revoked in the 1990s.

Until 2007 and the introduction of the Joint Personnel Administration (JPA) system, Army Officers were issued with a six-digit Personal Number, as opposed to the eight-digit Army Number for enlisted personnel.

In the Royal Navy, prior to the introduction of JPA, service numbers were also of eight digits but began and ended with a letter, depending initially on the depot where the sailor was recruited.

A service number beginning with D designated a Royal Navy male rating, W a Royal Navy female rating, C male officers, and V female officers.

Following the introduction of JPA, all newly issued Royal Navy service numbers became an eight-digit number format beginning with 3, with no distinction made between male, female, ratings, officers, and Royal Marines.

The Armed forces of the United States introduced service numbers in 1918, and discontinued their use in 1974.

In 2011, the Department of Defense began implementing a new service number system in order to reduce identity theft.

Effective June 2011, the US military has introduced a plan to eliminate the use of Social Security Numbers on military and dependent ID cards and replace them with a service number, in an effort to prevent identity theft against members of the armed services.