forgive my ignorance but i don't know near as much about the Lee Enfield family as i should.

i just picked up a 1943 Long Branch No.4 Mk.1 that has a Mk1 rear sight on it. my question is, would that have been on the rifle during the war or would that sight have been added post war? i never see any WWII pictures of the No.4 with anything but the "L" shaped sight.