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.
Light tanks of the United Kingdom
The biggest change from the Mark IV to the Mark V was the introduction of a three-man crew. The turret now carried the commander and the gunner who was also the radio operator. The increase in the crew size made a lot of difference to the tank's effectiveness and spread the maintenance load. Until then, the commander had to direct the driver, navigate, and operate the gun. If troop commander, he also had to direct the other tanks and their fire.