Tank
With World War II the multi-turreted tanks proved impracticable, and as the single turret on a low hull design became standard, crews became standardized around a crew of four or five. In those tanks with a fifth crew member, usually three were located in the turret (as described above) while the fifth was most often seated in the hull next to the driver, and operated the hull machine gun in addition to acting as a co-driver or radio operator. Well-designed crew stations, giving proper considerations to comfort and ergonomics, are an important factor in the combat effectiveness of a tank, as it limits fatigue and speeds up individual actions.
Tank
Strategic mobility is the ability of the tanks of an armed force to arrive in a timely, cost effective, and synchronized fashion. For good strategic mobility transportability by air is important, which means that weight and volume must be kept within the designated transport aircraft capabilities. Nations often stockpile enough tanks to respond to any threat without having to make more tanks as many sophisticated designs can only be produced at a relatively low rate. The US for instance keeps 6,000 MBTs in storage.