One of the things I like the most when looking at old photos is looking at the cars and buildings.
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Those are some of the best things for dating a photo, plus advertising and branding. That International truck was a difficult one, there's not a lot of information on that model. I'm just guessing that it's the L-190, there are a few different models that look the same. Plus I couldn't find any reference to the military using those models. The tow behind military busses are another thing that couldn't find any information on. Maybe they were a concept being tested by the Marines.