Service number 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 term as well . Social Security Number s may be seen as types of service numbers . The term " serial number " is often seen as 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 AIF 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 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 . The problems inherent in this scheme were acknowledged and all members of the Second AIF 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 - Western Australia ; T - Tasmania ; D - Northern Territory . The serial numbers of female soldiers followed this with an F . AIF serial numbers then had an X . A low number indicated an early enlistment . General Sir Thomas Blamey was VX1 . Soldiers transferring from the Militia often kept their old number with 100 , 000 added , while PMF officers had 200 , 000 added . Canada . Canada began using " Regimental Numbers " during the First World War . During the Second World War , units were allocated blocks of Regimental Numbers to issue out , usually in the 5 or 6 digit range , though extremely low numbers were also possible due to the blocks . The Social Insurance Number ( SIN ) replaced the regimental number in the 1960s . The SIN was itself replaced by a Service Number in the 1990s . 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 . The new Service Number used a random alphabetic letter and 8 numbers in the same format as SINs to avoid changing service forms . Nazi Germany . In Nazi Germany , the equivalent of a service number was known as a " membership number " which were issued by various Nazi groups based on when a person had initially joined . Nazi membership numbers were also preceded by the name of the organization to which the number applied . For instance , a person who was both a member of the SS and Nazi Party would state their numbers ( as an example ) " " NSDAP # 15337 und SS # 4436 " " . Membership numbers were considered extremely important in the Nazi system and to hold a low membership number was almost more important than what rank an individual presently had been granted . The Wehrmacht did not use service numbers in the same sense as their western military counterparts . Soldiers were inducted in their home districts , and identity recorded in a master roster book . A position in the roster book served as a unique identifier ; this number was recorded in the soldier ' s paybook , and was stamped on the soldier ' s " Erkennungsmarke " ( identity disc , or " dogtag " ) . Hong Kong . Current number of officers use a 5 digit number and are worn by all ranks below senior officers . The same numbering pattern is used by Correctional Services and Fire Services . United Kingdom . Soldiers in the British Army are given an eight - digit number , e . g . 25232301 . Prior to 1920 each regiment issued their own service numbers which were unique only within that regiment , so the same number could be issued many times in different regiments . When a serviceman moved , he would be given a new service number by his new regiment . Commissioned officers did not have service numbers until 1920 . The modern system was introduced by Army Order 338 in August 1920 . Numbers were then a maximum of seven digits , later groups of numbers up to eight digits were added . Until 1960 , National Servicemen who voluntarily remained in the Armed Forces continued to use their National Service numbers . Until 2007 and the introduction of the Joint Personnel Administration ( JPA ) system , Army Officers were issued with a six - digit service number . Newly commissioned officers now receive an 8 - digit service number , but 6 - digit Officers ' numbers issued prior to the introduction of JPA remained unchanged . 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 . The first letter designators were : P ( Portsmouth ) , C ( Chatham ) , and D ( Devonport ) , with the final letter being a meaningless checksum . Later , the designators were re - assigned and were used to distinguish between men and women within the Royal Navy as well as to distinguish between Officers and Ratings . 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 . P designated a Royal Marines Other Rank , while N a Royal Marine Officer . Following the introduction of JPA , all newly issued Royal Navy service numbers became an 8 - digit number format beginning with 3 , with no distinction made between male , female , Ratings , Officers , and Royal Marines . United States . The Armed forces of the United States introduced service numbers on February 28 , 1918 and discontinued their use in 1974 . The first U . S . military member to hold a service number was Arthur Crean . The following formats were used to denote U . S . military service numbers : Social Security Numbers are today used as the primary means to identify members of the U . S . military . The common format for a social security numbers is 123 - 45 - 6789 . 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 . All members are expected to have been granted the new service number by 2015 .