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.
Battle of France
The German Army lacked a formidable heavy combat tank like the French Char B1. In armament and armour, French tanks were the stronger designs and more numerous (although the German vehicles were faster and more mechanically reliable). But while the German Army was outnumbered in artillery and tanks, it possessed some critical advantages over its opponents. The newer German "Panzers" had a crew of five men: a commander, gunner-aimer, loader, driver and mechanic. Having a trained individual for each task allowed each man to dedicate himself to his own mission and it made for a highly efficient combat team. The French had fewer members, with the commander double-tasked with loading the main gun, distracting him from his main duties in observation and tactical deployment. It made for a far less efficient system. Even within infantry formations, the Germans enjoyed an advantage through the doctrine of "Auftragstaktik" (mission command tactics), by which officers were expected to use their initiative to achieve their commanders' intentions, and were given control of the necessary supporting arms.