Tank
With World War II the multi-turreted tanks proved impracticable, and as the single turret on a low hull design became standard, crews became standardized around a crew of four or five. In those tanks with a fifth crew member, usually three were located in the turret (as described above) while the fifth was most often seated in the hull next to the driver, and operated the hull machine gun in addition to acting as a co-driver or radio operator. Well-designed crew stations, giving proper considerations to comfort and ergonomics, are an important factor in the combat effectiveness of a tank, as it limits fatigue and speeds up individual actions.
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.