Another member had mentioned a guard car for use with M/T Balloon Car. Found there was such an animal !!! Built "about" 1942. It's in a museum in AR. Beautiful pics of interior and a pic of one 4-wheel truck. CANNOT find a pic of this @#%&*^! thing !!! It would be GREAT with Balloon Car and other DODX shipments. GRRR !!! WWII ended "a couple" years ago. Don't think it would be a threat to National Security to view a pic.
Particularly since there are online photos of other guard cars... heavily fortified cabooses if I recall correctly. I think there's a DOD equipment photo page out there... but with my "excellent" filing system I can't find the link right now.
I did some quick research and read that these type cars of the 1940s era were converted troop kitchen cars. I found this pic of such a car with an added cupola: Modern days we would be looking at a caboose? Below is the USN heavily armored caboose/guard car used when transporting nuclear material.
If you want a custom project, you could build a nuclear weapons guard car... Can you see this gallery? I created a gallery in Flickr for images I wanted to save for later reference, as I'd like to build a nuclear weapons train (retired since the 80s), pictured in this gallery. https://www.flickr.com/photos/123416308@N03/galleries/72157713622617197/
