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.
United States Army enlisted rank insignia
In terms of command, the rank of a person typically determines what job and command the soldier has within a unit. For personnel in US Army mechanized infantry, a Bradley infantry fighting vehicle (M2A2) is commanded by a Staff Sergeant, the gun is manned by a Specialist or Sergeant and the driver is Specialist or below. For armor, the Abrams main battle tank (M1A2) is commanded by a captain, lieutenant, sergeant first class or staff sergeant; the gunner is a staff sergeant or sergeant; the driver is a specialist, private first class, PV2 or PV1; and the loader is a specialist or below.