This is something of a work in progress and I only stumbled upon these number series when I was doing some research on a DCM winner for a friend.
The 1st Highland Brigade comprised the 1st, 2nd and 3rd City of Aberdeen Batteries and the 1st Highland Ammunition Column. Here's the important point. Despite all being administered by the same County Territorial Force Association, the City of Aberdeen, each of the batteries and the ammunition column operated their own regimental number series. I have not researched this unit much beyond November 1915 but here's what I have found out so far.
1st City of Aberdeen Battery
Started numbering from 1 in April 1908 from a number series extending to 999. When the TF was re-numbered in 1917, the battery issued numbers between 630001 to 630300.
2nd City of Aberdeen Battery
Started numbering from 1000 in April 1908 from a number series extending to 3000. When the TF was re-numbered in 1917, the battery issued numbers between 630301 to around 630574.
3rd City of Aberdeen Battery
Started numbering from around 3001 in around 1911 (I am unclear when this battery was formed)from a number series extending to 4000. When the TF was re-numbered in 1917, the battery issued numbers from around 630575.
1st Highland Ammunition Column
Started numbering from the high 3000s in April 1908. The lowest number on my database is 4005 issued in 1911. When the TF was re-numbered in 1917, the battery issued numbers from around 630840.
The significance of understanding this, particularly if your RFA ancestor was serving in the 1st Highland Brigade before late November 1915 is that if you know his regimental number, you'll also be able to identify which battery he served with, or whether in fact he served with the ammunition column.
For instance the men with the regimental numbers 289 (1st City of Aberdeen Battery), 1276 (2nd City of Aberdeen Battery), 3340 (3rd City of Aberdeen Battery) and 4128 (1st Highland Ammunition Column) - all of these units forming the 1st Highland Brigade RFA - enlisted in 1911.
Treat the number ranges above with a little caution. This is not an exact science, but I have enough data to be able to see significant patterns emerging for this Territorial Force artillery brigade in Aberdeen.
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