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.
Mark IX tank
The crew proper consisted of a driver sitting on the left and a commander sitting to the right of him (the first time in a British tank making this concession to the prevailing traffic conditions in France), a mechanic, and a machine gunner who could man a gun in a hatch at the rear. A second machine gun was fitted in the front. Designed as an armoured personnel carrier, the type had elements of an infantry fighting vehicle, as along each side of the hull there were eight loopholes, through which the soldiers could fire their rifles. Four of the total of sixteen loopholes were in the four oval doors (two to each side) through which soldiers could embark and disembark.