In expansion of what friends have so expertly found so far:
Men of the Royal Field Artillery served in all theatres of war and there were (haven't counted them all!) 1500 or so batteries in which he might have served, many of which were in India and/or Mesopotamia (present day Iraq mostly). So as far as specific information is concerned, that is likely to be it I'm afraid.
More generally, his service in India would have been on garrison duties rather than fighting. The campaign in Mesopotamia is covered here
http://www.1914-1918.net/mespot.htm. There would have been RFA units in most if not all of the 8 Indian Divisions and the one British Division that took part. That division had six RFA brigades each with 3 or 4 batteries and he could have been in any of the Indian divisions that had RFA brigades so I fear it is needle in the haystack time.
maxD
