While the tank was invented and initially fielded during World War I, World War II was really the first conflict to feature large scale armor formations, and put the theory of the tank into practice. Considerable thought had gone into the best doctrine for the use of the tank between the wars. Some doctrines were more successful than others. In the US during the interwar years, there were two primary schools of thought. Cavalry saw the tank as a replacement for the horse*, a means of rapid movement on the battlefield to turn flanks, raid the enemy rear, and exploit breakthroughs. Tanks should be light and fast. The tank would be the decisive arm, and all others should support it. The Infantry primarily saw the tank as a direct fire support asset for the rifleman. Tanks should be slow and heavy. The Infantry would be the decisive arm, and all others should support it.
That’s a gross oversimplification of the schools of thought, but sufficient for now. But a funny thing happened on the way to victory in World War II- it turned out, both major schools of thought were wrong.
The original US table for an armored division had two regiments of tanks, and one regiment of Armored Infantry, mounted on half-track personnel carriers. But it quickly became apparent that the “heavy” division was unwieldy, and, more critically, lacked enough infantrymen. Aside from the 2nd and 3rd Armored Divisions, eventually all US armored divisions in World War II would adopt a “light” table, with one regiment of tanks, and one regiment of armored infantry. In effect, the ratio of tanks to infantry went from 2-1 to 1-1. And by the end of the war, it wasn’t uncommon for an armored division to be augmented with extra infantry battalions, or even a regiment from a regular infantry division, in essence giving a ratio of 1-2.
Today we think of the tank as the ultimate tank killer. But prior to World War II, and indeed, through most of the war, US doctrine held that the very last thing tanks should be used for was killing tanks. That’s a large part of why the M4 Sherman was initially fielded with a rather anemic 75mm gun. The gun was quite suited for firing on bunkers and pillboxes. It’s rather poor performance against armor wasn’t thought to be a major handicap. By the end of the war, both the thinking on the best means of killing tanks, and the main armament had changed.
After the war, the rough numbers of infantry units to armor units was generally maintained at around 1-1. Armored Infantry eventually gave way to what we today call mechanized infantry. Carriers for the infantry have evolved from the half track through the M75 and M59 Armored Personnel Carriers, to the long serving M113 to todays M2 Bradley family.
In whatever vehicle they used, mechanized Infantry formations were always expected to operate alongside tank formations, with each arm supporting the other. Both armored and mechanized infantry divisions contained a balanced mix of tank and mech infantry units.
The fielding of the Bradley family, heavy on firepower, but light on numbers of actual infantrymen, made sense in western Europe when the US faced a Soviet Union with massive numbers of tanks and other armored vehicles, including thousands of BMP fighting vehicles and and BTR armored personnel carriers. Interestingly, the Soviets too had balanced formations of infantry and armor, though their mix of “motorized rifle” formations had a rough mix of one BMP formation (heavy on firepower, lighter on dismount infantry) to two BTR formations (light on firepower, heavy on dismount infantry).
The US saw the Bradley as needed to whittle down the numbers of Soviet vehicles. The problem was, the compromises needed to mount both an automatic cannon and the TOW missile launcher meant that something had to give, and that was the number of dismount infantrymen per vehicle. Whereas for many years the rifle squad was 11 or twelve men, eventually it shrank to 9 men. But in Bradley units, each Bradley could only deploy six, or maybe seven dismounts. And that’s under the cheery assumption that the unit was at 100% strength.
While that was generally acceptable for western Europe facing the Group of Soviet Forces in Germany (GSFG), for other theaters, that left a dearth of dismounts available for those missions that require large numbers of troops actually on the ground.
That lack of actual numbers of infantry, when history has shown that large numbers of infantry are required on the combined arms battlefield, was part of the impetus for the introduction of the Stryker Brigade Combat Team. The Stryker is often belittled in comparison to both the Bradley, and the M113. But the Stryker is not a replacement for either. Rather, it is a recognition that earlier light infantry units simply didn’t have the operational mobility to move around the battlefield. The weapon of the Stryker BCT isn’t the Stryker vehicle, it is the dismount rifleman.
No real point to all of this. Just putting some random thoughts down.
*Of course, not all Cavalry officers thought this. Many right up until about 1940 still saw the horse as a viable weapon of war.