I jumped ahead of what I was doing and went through both the 1948 and 1946
lists that were uploaded.

I found no C&O ventilated cars in 1946, but in 1948 there were three:

86812 - merchandise
86522 - clay
86824 - meal

They don't seem to have been too common around the Alexandria, Manassas,
Monroe, Potomac Yard areas in Virginia, as out of 1740 cars listed, only
21 were ventilated cars (VA and VM): the three C&O cars above, plus one
ACL, nine L&N, three SAL and five CG. The non-C&O cars were:

ACL 18023 - merchandise
CG 57180 - clay
CG 57478 - merchandise
CG 57560 - pipe
CG 58048 - merchandise
CG 58156 - meal
L&N 15731 - machinery
L&N 15297 - merchandise
L&N 15737 - boards
L&N 15741 - yarn
L&N 15883 - paper
L&N 16048 - yarn
L&N 16327 - furniture
L&N 98041 - tin plate
L&N 98834 - cement
SAL 28680 - lumber
SAL 89430 - merchandise
SAL 89870 - merchandise

The 1946 list lists 1938 cars, of which only eleven were VA or VM (none
C&O). They were:

ACL 17094 - lumber
ACL 18102 - Excelsior (I have NO idea what this might have been)
CG 56446 - merchandise
CG 55469 - merchandise
CG 56179 - cement
L&N 17718 - ties
N&W 65597 - lumber
N&W 65646 - lumber
SAL 79509 - merchandise
SAL 89024 - clay
SAL 89303 - niter (??)

From all this I would gather that ventilated cars were used in all manner
of service, much like boxcars...

I hope this was at least interesting, if not very helpful. :)

Frank Valoczy
Vancouver, BC

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