When researching a First World War soldier, you may encounter a service number that includes a letter prefix such as “S/”, “G/”, “L/”, or “4/”. These prefixes were used by many regiments in the British Army and often provide important clues about a soldier’s enlistment.
Understanding these prefixes can help identify how a soldier entered the army, the type of unit he joined, and sometimes even the battalion he first served with.
Can a service number identify a battalion?
In some cases, yes.
During the First World War, most British infantry regiments issued service numbers in blocks that were associated with particular battalions or recruitment periods.
This means a service number may reveal:
-
the regiment a soldier joined
-
the approximate date of enlistment
-
the likely battalion he first served with
However, the answer is not always straightforward. Soldiers were frequently transferred between battalions during the war, especially after casualties or when new units were formed.
Why some WW1 service numbers include prefixes
During the First World War, the British Army expanded rapidly as millions of men volunteered for service. To manage the huge increase in recruits, some regiments introduced prefixes to distinguish between different categories of enlistment.
These prefixes helped separate:
-
regular soldiers
-
wartime volunteers
-
specialist enlistments
-
soldiers assigned to particular battalions or service roles
Because of this system, prefixes can sometimes reveal how a soldier joined the army.
Common WW1 service number prefixes
Different regiments used their own prefixes, but several appear frequently in First World War records.
S/ prefix
The S/ prefix often indicated a soldier enlisted for General Service, meaning he could be deployed overseas in one of the rapidly expanding New Army service battalions. Regiments such as the Black Watch (Royal Highland Regiment), Lancashire Fusiliers and Rifle Brigade (The Prince Consort’s Own) used the S/ prefix.
G/ prefix
The G/ prefix was used by some regiments to identify soldiers enlisted for wartime service rather than the pre-war regular army. The G/ prefix was often found amongst recruits from regiments including the Royal Fusiliers (City of London Regiment), Royal Sussex Regiment and the Buffs (East Kent Regiment).
L/ prefix
In certain regiments, L/ prefixes were associated with enlistment into specific battalions or recruitment schemes. It is most closely associates with Regular Army recruits. Used by the East Surrey Regiment, Middlesex Regiment and again the Royal Fusiliers (City of London Regiment).
Numerical prefixes (such as 4/ or 5/)
Some Territorial Force units used prefixes such as 4/ or 5/ to indicate the battalion a soldier joined. This prefix style can especially be seen in soldiers from the Leicestershire Regiment.
Because prefixes were not standardised across the entire army, their meaning often varies between regiments.
Why prefixes matter for family history research
Prefixes can be extremely helpful when interpreting First World War records.
When combined with the service number itself, they may help identify:
-
the regiment a soldier joined
-
the battalion he first served with
-
the approximate date of enlistment
-
the type of service he entered
However, prefixes should always be interpreted alongside other records such as medal rolls and service papers.
Example: interpreting a prefixed service number
A Black Watch (Royal Highland Regiment) service number in the range S/3000–S/9500 indicates enlistment into the 8th–10th (Service) Battalions between August 1914 and June 1915.
The S/ prefix helps identify the number as part of a wartime Service Battalion block. Soldiers in this range were typically volunteers who joined the Black Watch during the early expansion of Kitchener’s Army.
These battalions later fought in major campaigns including Loos, the Somme, Arras, and Passchendaele, while the 10th Battalion also served in the Eastern theatre.
This illustrates how a prefix, combined with the number range, can help narrow down a soldier’s likely battalion and enlistment period.
Use the Service Number Tool
If you have discovered a service number with a prefix, the British Army Service Number Tool can help interpret what it might reveal.
The tool analyses regimental number blocks and prefixes to estimate:
-
likely battalion
-
enlistment period
-
possible theatres of service
-
recruitment hotspots connected to the regiment
Why prefixes are sometimes confusing
Prefixes were not used consistently across the British Army. Different regiments adopted their own systems, and the meaning of a prefix in one regiment may differ from another.
In addition, soldiers were sometimes transferred between units during the war, meaning the service number originally issued at enlistment may not always reflect the battalion they later served with.
Because of this, prefixes should be treated as helpful clues rather than definitive answers.