steel so perhaps a value of 0 would be more appropriate for these vehicles?
No.
The "un-armoured" versions are given a 1 because they are sunk too easily in the game if they are given zero. The 1 rating is a compromise to playability. The "armoured" versions are given a 2. That's a design decision based on playability as well.
Don
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"You are never to old to rock and roll if you are too young to die".--- What do you expect to be doing when you are 80?