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.
Holt Manufacturing Company
As well as having a better power-to-weight ratio, a gasoline-engined tractor required fewer men to operate it. Competing steam engines typically required a crew of seven, including one highly skilled and well-paid, licensed "farm engineer". He was responsible for rising in the middle of the night to start the boiler fire to get up steam by first light. Steam traction boilers had a huge need for water and fuel, either coal or wood. Much of the seven-man crew's time was spent keeping it fueled.