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.
Amphibious Combat Vehicle
The ACV 1.1 is to carry 10–13 Marines, have a swim capability similar to the AAV, and have equal or greater mobility to the M1 Abrams tank. Although tracks are traditionally considered better for all-terrain mobility, the Marines believe wheeled vehicle technology has advanced enough to enhance survivability and mobility in a 35-ton-class platform; the Marine Personnel Carrier technology demonstrator used "in-line" drive technology that enabled all four wheels on each side to pull together much like the way a track does which, combined with a higher ground clearance and central tire inflation system, substantially closes the maneuverability gap and results in equal or better maneuverability than the M1A1 and better performance over the AAV. Improved technology used to inform requirements to build ACV 1.2 vehicles will later be applied to delivered 1.1 versions to upgrade them to 1.2 standard. Each ACV 1.1 vehicle will have a 3-man crew, and two vehicles will carry a reinforced rifle squad. Armament will consist of an M2 .50-caliber machine gun in a remote weapons station, with the potential to install a stabilized dual-mount M2/Mark 19 grenade launcher turret. Potential water speeds are for a ship-to-shore capability at 8 knots.