One of the most confusing features of British Army service numbers during the First World War is the appearance of large six-digit numbers issued to Territorial Force soldiers in 1917.
Many soldiers who had previously served with four- or five-digit numbers suddenly appear in records with completely new numbers. This was not a mistake or a transfer between regiments. Instead, it was the result of a major administrative reform known as the Territorial Force renumbering scheme of 1917.
Understanding this change can help historians and family researchers interpret many British Army service numbers from the later years of the war.
Why the renumbering happened
Before 1917, Territorial Force battalions issued their own service numbers independently. This created several problems as the war progressed.
Different battalions within the same regiment often used overlapping numbering systems. As units expanded, merged, or transferred soldiers between battalions, duplicate numbers became increasingly difficult to manage.
To solve this problem, the War Office introduced a new system in March 1917, issuing each Territorial battalion a unique six-digit numbering block.
How the new numbering system worked
Under the 1917 scheme, Territorial Force soldiers were issued new service numbers drawn from large blocks allocated to specific battalions.
These numbers usually fell within the 200000–300000 range, although exact allocations varied between regiments.
Once issued, the new number replaced the soldier’s original Territorial Force number in most official records.
Example: Middlesex Regiment renumbering
For example, service numbers between 200001 and 240000 were allocated to the 7th Battalion of the Middlesex Regiment, a Territorial Force battalion, during the 1917 renumbering scheme.
A soldier with a number in this range was most likely serving with the 7th (TF) Battalion when the new six-digit numbering system was introduced in March 1917.
The battalion served on the Western Front and fought in major campaigns including Passchendaele (1917), the German Spring Offensive, and the Hundred Days Offensive of 1918.
Because these six-digit blocks were issued to specific Territorial battalions, numbers within this range provide a strong indication of a soldier’s unit during the later stages of the war.
Why renumbering confuses researchers
The 1917 renumbering scheme means that many Territorial soldiers appear in records with two completely different service numbers.
A soldier might therefore appear as:
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an early four-digit Territorial number, and
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a later six-digit renumbered service number
Without understanding the renumbering scheme, it can look as though two different soldiers are involved when in fact both numbers belong to the same man.
Using renumbered numbers in research
Despite the confusion they sometimes cause, the 1917 numbers can actually be extremely useful for research.
Because the numbering blocks were allocated to specific battalions, they often provide a clearer indication of a soldier’s unit than earlier Territorial numbers.
This is one of the key historical patterns used by the British Army Service Number Tool when analysing service numbers from the later years of the First World War.