Chris, essentialy the UC was a delivery vehicle not an AFV. It was desiged to transport a Bren team and two Riflemen to a desired location while possibly under fire. On the insides of the rear compartment you will notice there are metal bars tacked on the sides to create slots. These slots held a leather bag with a dozen Bren mags. The bags also had a shoulder strap. I doubt that they were often used in this manner but we were still being trained in the drill after the war.
The Mortar and 6pdr carriers did much the same thing they delivered the weapon to the site where it was to be used then retired to await the "H for Horses" signal to come and pick the weapon up.
One piece of equipment that is not often mentioned is sand bags the drivers would often line the bottom of their compartment with them as extra protection against mines.
Having said all that we know there were many modifications to suit specialized purposes.

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