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.
Tanks in the British Army
A first offensive using 49 Mark I tanks took place on 15 September 1916, during the Battle of the Somme, under Field Marshal Sir Douglas Haig, with limited success. Not until 20 November 1917, at Cambrai, did the British Tank Corps get the conditions it needed for success. Around 400 tanks penetrated almost six miles on a 7-mile front. This was their first large-scale deployment in combat. Unfortunately, success was not complete because the infantry failed to exploit and secure the tanks' gains. The British scored another victory the following year, on 8 August 1918, with 600 tanks in the Amiens salient. General Erich Ludendorff referred to that date as the "Black Day" of the German Army.
The German response to the Cambrai assault was to develop its own armored program. Soon the massive A7V appeared. The A7V was a clumsy monster, weighing 30 tons with a crew of eighteen. By the end of the war, only twenty had been built. Although other tanks were on the drawing board, material shortages limited the German tank corps to these A7Vs and some captured Mark IVs. The A7V would be involved in the first tank "vs". tank battle of the war on 24 April 1918 at Villers-Bretonneux—a battle in which there was no clear winner.
Parallel to the British development, France designed its own tanks. The first two, the medium Schneider CA and heavy Saint-Chamond, were not well-conceived, though produced in large numbers and showing technical innovations, as for the latter type a petro-electrical transmission and a long 75 mm gun. The later Renault FT was the first operational tank with a "modern" configuration: a revolving turret on top and an engine compartment in the back; it would be the most numerous tank of the war. A last development was the superheavy Char 2C, the largest tank ever built, be it some years after the armistice.
Numerous mechanical failures and the inability of the British and French to mount any sustained drives in the early tank actions cast doubt on their usefulness—and by 1918, tanks were extremely vulnerable unless accompanied by infantry and ground-attack aircraft, both of which worked to locate and suppress anti-tank defenses.