Training Regiments

My grandfather was too old to see active service in WW2. I have been searching for ages for his WW1 records to no avail, although i know he was in the Royal Artillery. Just before Christmas, in a chance conversation with my father, he mentioned that my grandfather's WW2 details were on my aunts birth certificate in 1939. Well why didn't i think of looking on that? I am hoping to link the details with possible WW1 regiments but that is rather unlikely to happen, i know.
Anyway i have found out the details state his name as J C Martin Bombardier Training Reg Royal Artillery, His number is 1050666 but the first 6 may be a 5 as the certificate is folded and the number is faded!! He was 41. I have also been told that he served at Bovington, near Lulworth in Dorset, but i have no proof this is true, as yet.
By 1943 when his son was born he was a Sign Writer and not in the training regiment any more.

This got me interested in Training regiments and i found a few sites that have helped me to understand what they did and why they were created

BRITISH ARTILLERY IN WORLD WAR 2 RECRUITING & TRAINING
http://nigelef.tripod.com/recruitrain.htm

Also
http://en.wikipedia.org/wiki/Royal_Tank_Regiment