My late father-in-law who was a fireman/driver out of Dundee from the early 40's onwards described the Aberdeen fish trains as the hardest work he ever did. Passenger train timings with none of the breaks, (station stops).
In the early 50's departures from Aberdeen were at [1953 TT] 12:30 KX, 1:40 KX, 1:55 Law Jcn, 5:50 Edinburgh, 8:55 Manchester and 7:45 Perth. The makeup at that time would be ex LNER/ex LMS vans, mostly in bauxite (so looking like standard vans) with some insulated and increasing numbers of what became known as Blue Spots. Usually hauled by a Pacific or a V2. Very often, in fact, the exact same engines that visitors to Dundee regularly describe in photo captions as "being on standby" when actually they simply worked when the photographer was tucked up in bed.
I think nowadays we have very little sense of just how huge this traffic was and what was involved in getting it run without delays.
John