the tank, with all-round vision devices rather than the limited ones of the driver and gunner. He guides the gunner roughly onto target and guides the driver around turns and obstacles. Gunner – The gunner is responsible for laying the gun, the process of aiming an artillery piece at targets. It may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire, where firing data is calculated and applied to the sights. The term includes automated aiming using, for example, radar-derived target data and computer-controlled guns. Gun laying means moving the axis of the bore of the barrel in two planes, horizontal and vertical. A gun is "traversed" (rotated in a horizontal plane) to align it with the target, and "elevated" (moved in the vertical plane) to range it to the target. Loader – The loader loads the gun, with a round appropriate to the target (HEAT, smoke, etc.) as ordered by either the commander or the gunner. The loader is usually the lowest ranked member of the crew. In tanks with auto-loaders this position is omitted. Driver – The driver drives the tank, and also performs routine maintenance on the automotive features. Operating a tank is a team effort. For example, the loader is assisted by the rest of the crew in stowing ammunition. The driver is assisted in maintaining the automotive features. Historically, crews have varied from just two members to a dozen. 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. 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. 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