I believe that you may use it in an assault, provided that you do not need to physically move the trn from one post to another. For example, if the tank you are referring to is needed to attack Finland, then i believe that you may go ahead on the US’s turn. If, on the other hand, you needed to drop it in Algeria, then you would have to wait until after Russia’s next turn to move the trn down there.
The power of the trn’s bridging ability in this respect just struck me. This is too sweet. Am i right? Is this legal? How many times during a round may a trn bridge, 'cuz it looks like 3 !?!?!?!