Air forces assisted armoured formations during World War II by providing reconnaissance, interdiction, and close support, as well as putting down airborne troops in front of advancing spearheads when the occasion demanded. Between 1939 and 1942, this method of making war led to brilliant victories equal to any in history. Later, though, it became increasingly clear that there were certain limits to the armoured offensive. Since railways were too inflexible for the purpose, armoured divisions depended on motor convoys for the bulk of their supplies. These convoys themselves made extraordinary demands for fuel, maintenance, and spare parts, with the result that even the most carefully planned, brilliantly led armoured thrusts tended to lose momentum once their spearheads had reached 200 to 250 miles from base. Such an operational reach sufficed to bring down medium-size countries such as Poland and France but not a continent-size country such as the Soviet Union, which was also distinguished by a terrible road system. When the attacker did not enjoy air superiority, as often happened to the Allies before 1942 and to the Germans after that year, the logistic “tails” on which blitzkrieg tactics depended proved very vulnerable to attack by fighter-bombers. Occasionally, as at ʿAlam al-Halfaʾ in 1942 and again during the German counterattacks in Normandy in 1944, air power was able to halt armoured thrusts almost on its own.

Moreover, tanks, originally conceived as offensive instruments, turned out to be at least equally useful on the defense, especially when dug into the ground in “hull-down” positions and deployed with other weapons and field fortifications such as antitank ditches, mines, and barbed wire. Such a combination presented almost insuperable obstacles to the attacker, whose forces would be caught in a maze, cut into penny packets, and lured into killing grounds. Also, as other countries built up their armoured forces in imitation of the Germans, great tank-to-tank battles sometimes took place; but even here the visions of theorists such as J.F.C. Fuller, who had predicted all-tank armies maneuvering against each other like navies at sea, were seldom, if ever, realized. Even in North Africa, with its absolutely open terrain, victory usually went to the side that better knew how to combine armour with other arms such as artillery, antitank artillery, infantry, and, paradoxically, the very engineers whose efforts armour had originally been designed to overcome. From at least 1942, combined-arms warfare became the order of the day, and it remained so for decades to come.

Finally, the tank was not suited for every kind of terrain. Like the cavalry of old, armoured warfare was most effective in broad, open plains like those of northern France, the western Sahara, and southern Russia. In mountainous, forested, swampy, or built-up terrain, the role that tanks could play was necessarily limited, both because of diminished trafficability and because there was insufficient room for them to deploy. Though there were exceptions (witness the brilliant German stroke through the Ardennes in 1940), often tanks were of no use at all—or else they were reduced to supporting the infantry, as happened in Italy and, later, Korea. Since the tanks’ rotating turrets had to absorb the recoil of their guns, these were usually smaller in calibre than ordinary field cannon, so that, employed as artillery, tanks were costly and only moderately effective. Thus, armoured warfare was able to achieve its full potential only in certain theatres. In many others, including Southeast Asia and the Pacific, the role of tanks was more limited, and the old combination of infantry and artillery, now also supported by the air force, usually prevailed.