In my experience working with the army, there were, as in this case, vehicles transferred from the RAF and re-numbered in the BT series. One of the Constructors was used in the late Seventies by the Infantry Display Team, for towing a recovery trailer of a type I have forgotten, think the load was a FV432. The only thing that stuck in my mind, other than it being a BT number, was the name on the front, "Green Giant".