This will at least allow you to place "your" Regiment or unit in context. If on the other hand, your subject belonged to one of the many support units upon which the fighting units depended, researching its history can be a little more complex.
There were many hundreds of such units, sometimes as small as company size, and many of these were disbanded forever, quietly and without fanfare, almost as soon as the war in Europe was over.
Through the miracle of the internet, a legion of veterans' descendants have taken it upon themselves to research their fathers' pasts, if for no other reason than to gain a better understanding of 'the way things were' and 'what he went through'.
But in some cases today, we even find some of these middle-aged 'kids' coaching their veteran fathers in the mysteries of the internet, as the latter attempt to find whatever has been written about their service in those distant times.
Full explanations and instructions may be found on the Archives' Military and Civilian Personnel Records web page. These records will at the very least give you a basic sketch of your subject's military career, from date of enlistment to date of demobilisation.
At this point, having identified the basics of your subject's service, you have two choices as to how to proceed.All of this is available to you, but retrieving, and interpreting, what you need can be a frustrating and time-consuming experience if you don't know your way around.There are numerous private archivists who for a fee, can unearth and synthesize the information you require.Note down any details you can remember from conversations past, and ask other members of the family what they remember.If your subject had friends of the same age, approach them with an explanation of what you're trying to do, and ask them if your subject ever confided any information about his service.To this day, there are some who will not speak about the war to any others save 'those who were there'.