Thanks very much for your responses, guys. I had suspected that perhaps since the tank was a "hand-me-down" that it may not be in full working order, but as Judo mentioned the mission and diary made no mention of faulty equipment, which was confusing. However, I should mention that the T-55 was fully operational for me in its second mission, "Commando" - but sadly I have yet to pass it after 18 tries because of freezing.
To answer Moons question, I was lazing the stationary artillery in the first T-55 mission, and could not get a proper reading. I just shot them with a High-Ex shell though, so that was no real problem. Oh, and they were about 900m out from my position at the time.
On the flipping, I have had the Sherman from mission one flip, and also a few AFVs. Actually, I think one of them was allied to me, but the poor buggers wrecked. It is not a huge problem at all, just one that I wanted to fix if possible.
Thanks for trying to obtain info on the Global Realism option. I love the game, and want to get as much out of it as possible.
Thanks again for your help, folks.