The majority of infantry movement in the Second World War was still footbound. Large strategic movements, like bringing a corps from the reserves to the front line, would often be done by rail, but the movement from the rail depot to the front line would still usually be by foot. Even the vaunted Wehrmacht, which cast itself in the image of a heavily motorized modern army, still generally marched into battle on foot. Mechanized/motorized units, of course, would ostensibly load their units onto trucks or half-track armored infantry carriers, but this was the exception and not the norm. The German invasion of the USSR in the summer of 1941, for instance, saw the most modern infantry force in the world marching along side roads and dirt trails, throwing up clouds of dust 30 kilometers long as columns of exhausted, bare-chested men (and horses!) tried desperately to catch up with tank formations which had lunged hundreds of kilometers ahead of them.

The mobility difference between men and armor, incidentally, was one of the defining military problems of the mid-20th century. Tanks without infantry are vulnerable, and infantry without tanks lack striking power. Interwar theorists like JFC Fuller envisioned a fully mechanized mass of tanks and armored carriers, but the material realities of the time prevented this. Particularly given the economic devastation of the 1930s and the general unwillingness to give the military a blank check, it was not feasible even to build enough trucks for another massive continental war, let alone enough complex armored carriers. The British, with their relatively mature automotive industry, fared better in this regard than the Germans or the Soviets, though I would have to defer to someone else on the question of how fully motorized the British Army was during WW2. The Americans did enter the war with an enviable level of motorization, but even so, outside of the halftrack- and truck-mounted infantry of armored formations, GIs generally went into battle on foot. The American surplus of trucks was used more for keeping units supplied, especially the artillery. The Soviets, too, generally used their trucks (both Lend-Lease and domestic) to tow artillery and carry supplies. The exception here was the truck-borne infantry of the various mechanized units and cavalry-mechanized groups. Their frustration with the infantry's lack of protected mobility led, of course, to their efforts to mechanize the entire infantry force during the 1950s and early 1960s, culminating in the revolutionary BMP infantry fighting vehicle.