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.
Tank destroyer battalion (United States)
The first nine units were deployed during the Louisiana Maneuvers of 1941, equipped with towed 37 mm anti-tank guns (the largest gun that could be towed by a jeep) and 75 mm guns mounted on half-tracks (the M3 Gun Motor Carriage), and again in the Carolinas maneuvers that November. Their employment was judged a success—though not without some disgruntled voices in the armored branch arguing that the umpires had rigged the results—and on 27 November, Marshall ordered the establishment of a tank destroyer Tactical Firing Center at Fort Hood, Texas, under Bruce, and the activation of 53 new anti-tank battalions under the command of General Headquarters. The term "tank destroyer" was used from this point on, as it was seen as a more psychologically powerful term. On 3 December, all existing anti-tank battalions were reassigned to General Headquarters and converted to tank destroyer battalions.
The new tank destroyer doctrine was formally stated in Field Manual 18-5, "Tactical Employment, tank destroyer Unit", in June 1942. It laid down a focused doctrine—"There is but one objective of tank destroyer units… the destruction of hostile tanks"—and repeatedly emphasized an offensive, vigorous spirit. Tank destroyer units were expected to be employed as complete battalions, held in reserve and committed at critical points, rather than parceled out as small defensive strongpoints. The emphasis was heavy on mobility, and the ability to outmaneuver the attacking armor; this would feed into vehicle design, and cause the speed of a vehicle to be prioritized over survivability.