[Jon Skagfeld]

"Over hill, over dale,
As we hit the dusty trail,
And the caissons go rolling along"...

Sounds like the terms limber and caisson might have been interchangeable, depending on the time frame. See the first definition in Concise Oxford Dictionary, viz:

Ammunition chest or wagon;

The other definitions relate to large watertight cases open at the bottom, from which water is kept out by air pressure, used in laying foundations under water