This is a very rough guide and only covers batches of numbers that we know were allocated to particular Battalions at particular times. Many men were allocated numbers which do not fall into any of the number batches described below.
Every non-commissioned soldier had an Army number. These were not unique to that soldier until the re-numbering in 1920. It is very helpful to know your soldier's number.
Commissioned Officers did not have numbers in World War 1.
Prior to World War II, personal army numbers were engraved around the edges of campaign medals. This was not done from World War II onwards.
You may find the number sewn into clothes or written on personal records such as pay books. Please note that your soldier may have had more than one personal army number during his period of service if he served before 1920. If he transferred between Regiments he would have been allocated a different number with each transfer. Some members of the Territorial Army were re-numbered in 1917. You sometimes find men having two or three numbers without an obvious change of Regiment too. At this time army numbers were not unique and many different men in different Regiments shared the same numbers. A unique numbering system was introduced in 1920.
Army Numbers Allocated to Dorsetshire Regiment Soldiers from 1881 - 1920
In 1881 regular Battalions of Infantry Regiments allocated numbers starting with number 1 and working upwards.
From 1893, men in the 1st and 2nd Battalions the Dorsetshire Regiment were allocated numbers in the 4000-5000 range. By January 1899, the Regiment was issuing numbers in the 58** range.
The 3rd Battalion, which was the Special Reserve (formerly Dorset Militia), had a 4-figure number pre-fixed by a 3. For example 3/1234.
On the creation of the new Territorial Force (TF) in April 1908, men in the 4th (TF) Battalion were given numbers starting from 1. When the TF was renumbered in 1917, 4th Dorsets number block was 200001 – 225000.
Men in the 5th and 6th Service Battalions of the Dorsetshire Regiment in World War I had numbers ranging from the late 1900’s to the 11000s.
Soldiers with numbers in the 19,000 block were reinforcements sent to the 5th Battalion the Dorsetshire Regiment to replace casualties. Many of these came from the 3rd Battalion the Somerset Light Infantry (special reservists) or North Somerset Yeomanry.
The Dorset Yeomanry also had a new figure number system introduced in 1908. In 1916 they too were renumbered using numbers in a batch 230,0001 to 235,000.
Those with numbers between 10,000 and 11,000 were often in the 5th or 6th Service Battalions.
Army Numbers Allocated to Devonshire Regiment Soldiers from 1881 - 1920
In 1881 Regular Battalions of Infantry Regiments allocated numbers starting with 1 and working upwards. By January 1899 the 1st and 2nd Battalions The Devonshire regiment were allocating numbers above 5260, by July 1910 9000 had been reached and on 31st March 9952 was allocated.
When Britain went to war with Germany a few months later, men joining the newly formed Service Battalions were issued service numbers belonging to the same series as for the Regular Battalions.
On 14th August 1914 the number 10102 was allocated.
As regards the Territorial Force Battalions (4th, 5th and 6th), following reorganisation in 1908, each began numbering from 1 from 1st April that year. By 1914 numbers being allocated were 3 or 4 digits. In early 1917 all men serving with TF units abroad were given new 6 digit numbers with distinct allocated blocks:
4th Battalion 200001 - 240000
5th Battalion 240001 - 265001
6th Battalion 265001 - 290000
Other newly formed Territorial Force Units:
7th Battalion 290001 - 315000
15th Battalion 315001 - 340000
16th Battalion 340001 - 350000
Army Numbers After 1920
The British Army was renumbered in 1920. All soldiers were given a unique 7 digit number which remained with them throughout their service career. It is this number that you need when applying for a post 1920 Service Record.
The Devonshire Regiment was allocated numbers 5,608,001-5,662,000.
The Dorsetshire Regiment was allocated numbers 5,718,001-5,763,000.
The numbering system changed again in 1943 when all soldiers joining the army was allocated a number from one block commencing 14200001, regardless of Regiment.
Many thanks to Paul Nixon for the information provided, the information used is taken from his excellent blog post, which you can find here.