D. Scott Chatfield
> An attempt to improve engine room ventilation. Answer is on P.338 of Diesels of the Southern Railway 1939-1982 (Withers with Calloway and Wilson).
Just because it's in a Withers book doesn't make it correct.
I don't see how it would help "engine room ventilation." F-units did not have pressurized carbodies, and I don't see any vents on the box. Also note the box is on the front of the NP B-unit and the rear of the Southern A-unit.
To me the box looks like a roof-hung water tank from a passenger-equipped unit, but neither of these units were passenger-equipped. No pass-through steam lines either. Perhaps it was a water tank and they couldn't mount it flush because of something inside.
Doesn't appear to hold radio gear either.
So that leaves us with the only logical explanation: increased headroom so basketball players could use the toilet.