One of the most heartbreaking factoids I've discovered in the past few years is that the Soviets kept their armored vehicles under 36 tons in weight so that Soviet bridges could be built too light-duty for NATO armor (a M60 Patton tank, by comparison, weighs 50 tons). A consequence of this design decision is that Soviet tank crews had to be 5'8" or under.
I'm 6' tall.