I'm trying to find military service for my great uncle, John Stewart (b. 1921 Port Glasgow, Scotland).  He relocated to Natal, South Africa in 1936 at the age of 15.  I have been told by my mother that he fought in WWII, and that she thinks he may have been a prisoner of war.  My question is whether  there would be a separate South African army that fought in the war, or if he'd have been part of the British forces.  Either way, does anyone have any suggestions on how I might find his military records.  Any thoughts or suggestions would be very helpful!
Jennifer