Remember riding in the military 'cattle cars'?
To transport troops efficiently they used truck tractors
pulling trailers that had crude lumber sides & seats.
Much more efficient for troops dressed for field work
than any bus would be.
Routinely used to get Marines from barracks out
to the training or operation areas.
I remember for the 'riots'/'protests' in Washington DC
being transported from Quantico Va. to Wash. D.C.
in them.
Here are pictures and other information:
http://www.dustyfile.com/the-army-cattle-car
https://radiofreewis.blogspot.com/2014/06/blog-post.html