Jim Dick wrote:

This situation happened in the PNW. A NP document listing reasons why additional fifty foot double door boxcars needed to be purchased gave the following: During the early 1940's and during WWII, defense shipping from east (of the Mississippi) and auto traffic from Detroit provided plenty of fifty foot double door boxcars the lumber mills craved. They could load these and send them home in the general direction. ( a well balanced siuation)

Then as the war traffic winded down and auto factories in California opened up (Richard Hendrickson's post 89730), this created a need for additional cars of this type.
And from what I have found, given a choice - the mills preferred fifty footers over forty footers. Perhaps Tony Thompson can comment on that regarding SP shippers. For NP/SP&S it certainly was true.

Yes, I have copies of some SP memos about confiscating empty 50-ft. double-door cars throughout the system, and moving them to Oregon for lumber loading. It's evident in both SP records and in the ORER that SP regularly purchased lots of flat cars and double-door cars, in significant part to protect lumber traffic. That's why lumber trains on the SP were VERY heavily home-road cars.

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