On Mechanization and Combined Arms.

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.

8 thoughts on “On Mechanization and Combined Arms.”

  1. While the two main schools of thought on armored warfare might be a bit more complex than you had portrayed, you nailed the essence of them.

    Our own doctrinal thinking did not change despite ample evidence as far back as Spain that the most efficient and lethal killer of tanks were other tanks, is rather inexcusable. It was certainly inexcusable in 1942, after all that had transpired in France and Russia and North Africa, that we would have not understood those lessons. Had we followed British advice and mounted a somewhat-shortened 17 pdr onto an M4 when the idea was proposed, we could have had ample (and lethal) tank killers from D-Day forward.

    1. The Brits offered us Fireflys before D Day, but the US Army declined, believing still in the virtues of the TD. After the Bulge, when the US Army decided maybe some Fireflys might be of some use, and ordered 245 of them, the were not delivered until mid-April 1945. I think we just gave them back.

  2. The most educational thing I ever read with regards to mechanized infantry in the modern age was “The Pentagon Wars” by James Burton. The HBO movie had some funny moments (especially the poor O-6 who was stuck in staff officer hell for 4 presidential terms) but the book really shines, especially in its description of how the Bradley almost turned into a disaster due to DoD and contractor incompetence. I highly recommend this book for anyone that wants a real education on how mechanized infantry were seen supported during the 1970s and 1980s.

  3. Ok, I have to speak up here on part of this article. The 75mm was an effective anti-tank weapon during the first part of WWII. Against Panzer III and IV’s the 75mm armed M4’s were as good if not better armed. It was only the arrival of the Tigers that the 75mm started to lose some of its effectiveness. However, M4’s could consistently achieve penetrating hits on the flanks and rear of Tigers and Panthers.

    Although the Army was sluggish in adopting the 76mm for the M4, for a variety of reasons, the 76mm was comparable to the 17pdr with the advantage of not having to have the turret redesigned or a new system manufactured. The 76mm was already developed and could be produced without having bring in a new design.

    In 1944, there were a number of tests conducted by the British and American forces. The British, who had been fielding a new sabot round, found that even though the penetrator might be superior, and there were questions about that, the round was very inaccurate (at 400 yards, it was hitting about 56% of the time versus the more conventional AP rounds which were hitting 90% of the time. The accuracy got worse the further back they move.). In August, 12th Army conducted a formal test over two days against captured German Panthers with just about every type of cannon they had in the arsenal, including borrowing British tanks with British crews.

    The tests found that the two best guns were the 76mm firing HVAP rounds and 17pdr firing APCBC rounds. The 17pdr had a slight edge, but neither could reliably penetrate the front armor of the Panther. Incidentally, the most common German weapon for tanks was not the 88mm, it was 75mm.

    1. Bill, I have to challenge some of what you say. The M3 75mm low-velocity gun on the M4 may have been a tank killer against the “second string” armor of Italian and early variant III and IV in North Africa, but when the upgunned Mk III (5cm KwK 39 L/60) and Mk IV (7.5cm KwK 40 L/43 and L/48) appeared in larger numbers, the Sherman was badly outgunned. At combat ranges (1,000 yards), the Sherman’s M3 cannon was thoroughly inferior to the 7.5cm KwK40 L/43 and L/48. Both the German 7.5cm guns could penetrate any armor on the Sherman at that range with ease, and the 5cm L/60 was capable of penetrating all but the front glacis. The Sherman’s M3 75mm could not penetrate the hull armor of the Mk IV and would struggle to defeat the armor of the Mk IV turret and the frontal armor of the much smaller Mk III.

      The reason I mention the 17pdr is that the Brits had worked out much of the problems that the 76mm M1A1/A2 required solving (and had only started) by mid-1943. The US clinging to the “infantry support” doctrine and failing to recognize the lessons of three years of war was the cause of an exceedingly poorly armed medium tank that cost the lives of thousands of crews. A far more capable and lethal option was available.

    2. Bill, you are spot on here. A lot of the “coffee table books” will offer comparisons between the M-4 and other tanks, without walking through the details. As you point out, the Sherman was a damn good tank when introduced… and was able to outgun most adversaries encountered up to the fall of ’44. But the “coffee table books” will offer comparisons between the M-4 (medium) and Tiger (heavy) without pointing out the real positive points of the M-4.

      One of the myth about the M-4 is that a better gun might have been in the turret by mid-1944, but for some administrative action in the states. Reality is that up until the end of July, the tankers at the front simply preferred the 75-mm for its HE performance. Indeed, there was a call from the divisions for more 105-mm howitzer armed M-4s. OTOH, the 76-mm guns received criticism for lack of HE performance – shell walls were thicker to deal with the higher bore pressure, thus each round carried less punch. As today, the tankers more often found themselves working in support of infantry than going toe-to-toe with Tigers…. as we loop back to the combined arms discussion.

  4. On a good note, I will be watching a brigade defense in about 5 hours. Heavy forces fighting in Germany once again. It is a very Joint force, with Danish LRS out front, US CAV troop in screen, and US and Romanian battalions defending, each of which has Multinational companies attached. Going to be interesting.

  5. Brad,

    As Max Smart said….”Missed it by this much!”

    Good rundown but 1 correction and one additional bit of info.

    The armored infantry and tank battalions in the “light” armored divisions were not organized into regiments. They were stand alone separate battalions. For instance, the 54th Infantry Regiment was broken up in 1943 and its 3 battalions were designated as 20th, 54th and 60th Armored Infantry Battalions. Same with the 3 armored battalions and 3 armored field artillery battalions. A division had 3 combat command headquarters and battalions were rotated amongst the combat commands as needed based on mission.

    The 9 man rifle squad became universal for another reason. They were called the 6th Light Infantry & 10th Mountain Divisions. When the Army wanted to expand in the mid-1980s from 16 to 18 divisions it was told you have to do it without raising end strength….find the manpower slots within your current strength. So the Army went from 11 in a squad to 9 across the board. But there still was not enough….so what did the Army do? It came up with T-Rations and contract cooks so the number of cooks needed was reduced.

    Voila! 2 each 2 brigade light infantry divisions!

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