Tank
Most modern tanks most often have four crew members, or three if an auto-loader is installed. These are the:
Historically, crews have varied from just two members to a dozen. For example, pre-World War II French tanks were noted for having a two-man crew, in which the overworked commander had to load and fire the gun in addition to commanding the tank. First World War tanks were developed with immature technologies; in addition to the crew needed to man the multiple guns and machine guns, up to four crewmen were needed to drive the tank: the driver, acting as the vehicle commander and manning the brakes, drove via orders to his gears-men; a co-driver operated the gearbox and throttle; and two gears-men, one on each track, steered by setting one side or the other to idle, allowing the track on the other side to slew the tank to one side.
Tank
The three traditional factors determining a tank's capability effectiveness are its "firepower", "protection", and "mobility". Firepower is the ability of a tank's crew to identify, engage, and destroy enemy tanks and other targets using its large-calibre cannon. Protection is the degree to which the tank's armour, profile and camouflage enables the tank crew to evade detection, protect themselves from enemy fire, and retain vehicle functionality during and after combat. Mobility includes how well the tank can be transported by rail, sea, or air to the operational staging area; from the staging area by road or over terrain towards the enemy; and tactical movement by the tank over the battlefield during combat, including traversing of obstacles and rough terrain. The variations of tank designs have been determined by the way these three fundamental features are blended. For instance, in 1937, the French doctrine focused on firepower and protection more than mobility because tanks worked in intimate liaison with the infantry. There was also the case of the development of a heavy cruiser tank, which focused on armour and firepower to challenge Germany's Tiger and Panther tanks.