There is of course quite a difference in military use and civilian. In service a driver wouldn't move off without a ''driver, advance'' command from the man who can see best.
In civilian use, it's usually the driver who makes that decision. I always insist that passengers climp up the front for the reason Chris states, so that I can see them!
How does Bodge climb up? Towing eye, final drive housing, roof plate, turret top (all good so far) drivers head, drivers shoulder, turret top, into cupola....... Bless him!:-D