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.
Tanks in the Spanish Army
The first 50 T-26 tanks which arrived in Spain, under the command of Krivoshein, were crewed by Soviet personnel. Nevertheless, the Soviet lieutenant colonel opened a training school in the town of Archena, near Cartagena, recruiting mainly truck and bus drivers from cities such as Madrid and Barcelona. The next month, he opened a second school in Alcalá de Henares, north of Madrid. However, only Communist soldiers were allowed to crew Soviet tanks, and as a result the pool of soldiers to recruit from was narrow and often less adept drivers were picked over better ones, due to their political ideologies. For example, in one instance a tank commander broke contact with the enemy because he had not learned how to fire his main gun. Furthermore, at first, the Soviet trainers did not have interpreters to communicate with their Spanish students.