Ever since I was a kid (and that was quite some time ago, frens), the principle means of heavy military equipment like this was by rail. And that includes shipping from manufacturers' facilities to military facilities. I cannot recall how many such rail shipments I have seen in my lifetime, because I grew up in a home next to a railroad and saw these things all the time.

All these tanks and personnel carriers look brand new, not a blemish on them. So I think these are being shipped from manufacturing contractors to the military as the main possibility.

Sure, there might be something going on that we don't know about, but don't overlook the possibility that they are just new items being shipped.