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 desant
Today, tank desant is considered a wasteful and human-costly improvisation, which, in the opinion of some writers, was adopted by the Red Army because they failed to appreciate the problem of tank–infantry cooperation. However, this is not supported by historical analysis, and there is evidence that tank desant was used as early as 1937 during the Spanish Civil War. On 13 October, during the Aragon Front advance in the area of the Fuentes de Ebro, the 1st Independent Tank Regiment (Republican Army), using BT-5 tanks attached to the XV International Brigade, conducted a tank desant mission with the attached 24th Infantry Battalion of the Spanish army ("24ta de Voluntarios", commanded by Captain Aquilla). But lack of coordination and communication between the Soviet crews, who had just completed a march, and the Spanish infantry resulted in sixteen tanks being either destroyed or disabled (some salvaged) and 37 tank crewmen becoming casualties.