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. Engineering constraints A noted author on the subject of tank design engineering, Richard Ogorkiewicz, outlined the following basic engineering sub-systems that are commonly incorporated into tank's technological development: Mobility of tanks (through chassis design) Tank engines Tank transmissions Suspensions and running gear Soil-vehicle mechanics Tank guns and ammunition Ballistics and mechanics of tank guns Vision and sighting systems Illuminating and night vision systems Fire control systems for main and auxiliary weapons Gun control systems Guided weapons armour protection Configuration of tanks To the above can be added unit communication systems and electronic anti-tank countermeasures, crew ergonomic and survival systems (including flame suppression), and provision for technological upgrading. Few tank designs have survived their entire service lives without some upgrading or modernization, particularly during wartime, including some that have changed almost beyond recognition, such as the latest Israeli Magach versions. The characteristics of a tank are determined by the performance criteria required for the tank. The obstacles that must be traversed affect the vehicles front and rear profiles. The terrain that is expected to be traversed determines the track ground pressure that may be allowed to be exerted for that particular terrain. Tank design is a compromise between its technological and budgetary constraints and its tactical capability requirements. It is not possible to maximise firepower, protection and mobility simultaneously while incorporating the latest technology and retain affordability for sufficient procurement quantity to enter production. For example, in the case of tactical capability requirements, increasing protection by adding armour will result in an increase in weight and therefore decrease in mobility; increasing firepower by installing a larger gun will force the designer team to increase armour, the therefore weight of the tank by retaining same internal volume to ensure crew efficiency during combat. In the case of the Abrams MBT which has good firepower, speed and armour, these advantages are counterbalanced by its engine's notably high fuel consumption, which ultimately reduces its range, and in a larger sense its mobility. Since the Second