Sadly, my reference materials are still packed away.
Memory says it's a 10 ton semi tractor in the M1nnn range with a M-1000 low-boy trailer
But, that may be the HET (M-1070) combo that I'm recalling.
Going to wiki's list of all "M-" vehiclss, it's probably an M757 or M626 truck with an M-670 trailer.
But, I'd not be surprised if some were moved with one of the 7½, 8, or 10 ton prime movers and a dolly/caisson to haul an M15 low-boy.. What with red-legs often having to work with what they have, not what is supposed to be on TOE.