I can't argue with the photo and I only joined in 1963. I can only guess that the small arms school at Hythe (where the handbook was written up and photographed) still had old GSTP's in stock (General Service Time Pieces ?). Like most things, they were probably obsolescent as opposed to obsolete. On the courses the watch was important for observation of sentry movement, arrivals of high ranking people who make regular apearances or regular patterns of movement. Best to get mortars in then - and the snipers can remain concealed, move on and repeat the process