Remember the DOD didn't exist during WWII. Before 1947, we had the separate Navy Department and the War Department. Why is this important to your discussion? Because pre-1947 manuals for these weapons will be found in separate sections in archives. My first real job in the academic library world was in the Government Documents Department at the University of Virginia, which was a designated GPO depository (there are two of these in every state). As such we held paper copies of perhaps a million government documents and publications. I spent a lot of time break time looking at DOD materials, but was delighted to discover that we also had even older stuff up to 1947 in a separate War Department section, including a few manuals on military rail transportation (mandatory FC content). If you are looking for older stuff about 1942 guns on railroad cars, you are going to need to look for War Department documents. Sadly many of these older pieces have never been digitized.

This isn't about railroads, per se, but one of the prizes I found was a War Department book with "builder's photos" of various trucks supplied to the Army. Many of these were more-or-less off-the-shelf 1940 Ford, GMC and Dodge trucks. Except for tires and paint, these were virtually identical to trucks sold to the civilian firms, and many were later sold off as surplus after the war (especially fire engines). I copied out many of these for modeling purposes.

Yours Aye,

Garth Groff (retired paraprofessional librarian)  🦆