Further to the above, I can't find any specific mention of the 203rd Seige Battery in all the papers I have here, but I can tell you that a huge number of batteries were involved in the Cambrai Offensive at this time and in particular the Battle of the Canal du Nord at the end of September. It is highly likely that the 203rd would be amongst them, but I am sure that somebody with a bit more knowledge and expertise on this site will be able to put you right. Have you checked with the National Archives at Kew to see if there is a surviving War Diary for the 203rd?