First of all thanks so much David for your reply 7 months ago!!! I am not very good with this kind of thing and hadn't seen your reply!! So sorry.
I know a lot about the Mackay family but don't know what happened to William Sherris Mackay. He was born in Aberdeen, Scotland on 6 July 1864, son of David Mackay who was a VC recipient (lots about him on the Internet). He died in South Africa on 19 July 1945. A couple of his children were born in Monmouthshire, Wales but the others were born in the early 1900's in South Africa (one son, Herbert Kitchener Mackay was born in Bristol in 1898) I thought that because his one son was named "Herbert Kitchener" that he must have some kind of connection to the army! I haven't been able to find him on any shipping records but I have found shipping records for his wife and children. Two children born in Wales (1889 & 1892), then one in Bristol (1898), then some in South Africa (1902 - 1907) and the last one again in Wales (1908)! So he was getting around and it seems as if he must have been in the army.
My father died last year at the age of 91. I tried to ask him but his memory wasn't good. He did mumble something about being a Prisoner of War but I don't know if he could really remember or even knew who I was talking about. William would have been his grandfather on his mother's side.
Anyway, thanks again for the interest shown. Maybe you may not even see this reply of mine after all this time!