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.
Company (military unit)
In the United States Army, infantry companies are usually made up of three rifle platoons and a heavy weapons platoon; mechanized infantry companies are usually made up of three rifle platoons consisting of four infantry fighting vehicles (IFV) each and a command element containing two IFVs; tank companies are usually made up of three tank platoons consisting of four tanks each and a command element containing two tanks; support companies are typically divided into platoons of specialization that may contain additional special sections. A company is usually commanded by a captain, although in some cases they may be commanded by a first lieutenant or a major. Unlike its component platoons, a company typically has additional positions of supporting staff, such as an executive officer (XO), a first sergeant, a readiness/training NCO, and other positions (e.g., supply sergeant, armorer). The corresponding unit of artillery is always called a "battery". Similarly, the term "troop" is used for cavalry units, including both the horse-mounted units of history as well as modern armored cavalry and air cavalry units.