Note: The following article is excerpted from the book THE FORGE: The Decline and Rebirth of the American Military, November 12, 1918 to December 6, 1941 by Eric Hammel. The book is currently available in a $9.99 ebook edition published by Pacifica Military History in Kindle, Barnes and Noble Nook, and Scribd editions.

The American Armor Force in 1940

by Eric Hammel

Copyright 2008 © by Eric Hammel

The tank was invented by the British in the middle of the Great War solely as a means for crossing from their trenchline to a German trenchline in the face of the sort of heavy defensive fires that had been amply proven as fatal to infantrymen in the same setting. There was no other use contemplated for tanks; they were simply armored battering rams designed to advance at walking speed—2 or 3 miles per hour—while absorbing all manner of fire that infantry and even some artillery could put out. They could smash through barbed-wire barriers, so infantrymen advancing in their shadows could walk across that sort of barrier. The larger tanks were festooned with large cannon that could blow up barriers and defensive positions, and their several machine guns made them moving pillboxes that were more or less impervious to enemy machine guns.
Tanks, as conceived, designed, and built supported advancing infantry. Nothing more. There were large tanks and small tanks, but it all came down to the same thing. When the Germans got into the game, there were even tanks to fight other tanks, but they were sent into battle within the context of trench warfare.

 At the end of the Great War, the U.S. Army had manufactured under license 952 French-designed Renault M1917 (FT 17) 6-ton light tanks and 100 British-designed Mark VIII 40-ton heavy tanks. Except for a small number of virtually hand-crafted experimental models, the United States manufactured no tanks, per se, from 1920 through the early 1930s. The experimental models more or less kept pace with tanks that were designed abroad, but, unlike military aircraft, there was no commercial market for tanks, so no cross-pollination took place. Indeed, the heavy, rugged engines required to impel a heavily armed and armored vehicle forward over rough terrain did not exist in industry, so it was difficult to even experiment with fully armored yet reasonably speedy designs that might remotely have a chance of going into full-scale production.
The Americans studied tanks, but inasmuch as the lumbering tanks had not been of much use during the final stage of the Great War, when a highly mobile infantry army was employed mainly to achieve breakthroughs followed by long, swift pursuits of fleeing German troops. Thus, many American infantry officers became highly dismissive of tanks, which could not keep up with marching road-bound infantry.

  A cavalrymen who had commanded the AEF’s tank center, then a tank brigade, in France, George Patton Jr., was all for looking into further development of the fighting system. But Patton initially found very few fellow devotees in the cavalry branch, and he was given jobs far from the spheres in which he could further the creation of a tank force or even experiment with tank tactics. One professional officer who shared Patton’s enthusiasm was a brilliant 1915 West Point graduate named Dwight Eisenhower, an infantrymen who had been exposed to tanks when he was held back in the United States to train tank crews. The two hooked up early on and from time to time conspired to push for an armored corps. They were polar opposites temperamentally, but both had genius-level minds and shared a passion for tanks; they became fast friends despite a five-year difference in age, disparate ranks, and a world of breeding.

 Under the National Defense Act of 1920, the wartime Tank Corps was disbanded, cavalrymen were returned to the cavalry, and the tanks were placed in the hands of the infantry. All of the army’s tanks were formed into a “brigade” assigned to The Infantry School at Fort Benning, Georgia, and thus it became all but impossible for any specifically armor developments to take place.
Conversely, a few thinkers in the cavalry branch had interest in poking around the doctrinal edges of mechanized warfare, but the assignment of all the tanks to The Infantry School was the General Staff’s way of preventing that. So cavalrymen went ahead with experimental “combat cars,” small, lightly armored vehicles on treads that looked and acted remarkably like light tanks armed with several machine guns.
One of the cavalryman credited with knowing the most and thinking the best about tanks was Adna Chaffee Jr. A lieutenant colonel serving on the General Staff in 1930, Chaffee succinctly summarized the roles of tanks thusly: “ . . . first to assist the infantry of the combat divisions by directly preceding them and neutralizing the organized resistance in the main battle, [and] to use the light tank as the backbone itself of a force. . . . Along these lines may develop a great part of the highly mobile combat troops of the next war.”
In 1931, the cavalry was authorized to stand up the Mechanized Force—one experimental mechanized cavalry “regiment,” in reality a squadron of tracked combat cars and a squadron of wheeled armored cars and unarmored wheeled scout cars. The following year, the Mechanized Force was expanded to one mechanized “brigade”—the 7th—consisting of the mechanized cavalry regiment supported by two light artillery batteries. Most cavalrymen of the day turned up their noses at any notion that steel would, could, or should replace horse flesh, but a small, growing, and fairly influential minority leaned toward the use of fully tracked combat cars in the same roles cavalry traditionally filled—reconnaissance, raids on supply lines and against headquarters, screening the movements of large friendly formations, and pursuit of a broken enemy. Traditional horse cavalry had played almost no significant role in France during the Great War, and the cavalry branches of most western armies clearly foresaw a day when they would be abolished from the battlefield, so playing with combat cars wasn’t idle work. What this group of upstarts had in mind to begin with was the retention of traditional cavalry roles accompanied by a move from horses to full mechanization. They thus were at odds with the larger part of the cavalry community and the infantry’s advocates for an infantry-controlled tank force that would move across future battlefields at the speed of infantry (as the gods of war intended).

Where the mechanization-minded cavalrymen saw resurgence of the cavalry in dashing armored sweeps deep into enemy territory, the infantry continued to see tanks as a plodding aid to infantry’s getting from here to there under fire. There was in fact a place for both jobs on a modern battlefield, but, except for a sprinkling of visionary cavalrymen and infantrymen, neither branch was in the mood to give in to the other, and they certainly weren’t about to put their heads together. So, while the combat car enthusiasts in the cavalry toiled on in isolation, the infantry merely used its aging Great War tanks as props in the training of infantry officers—until these antiques ran out of spare parts and stopped running altogether. The only positive development for some years was the addition in 1936 of a second mechanized “regiment” to the 7th Cavalry Brigade.


The Cavalry’s Search for Relevance
After September 1939, there was no longer any reason to believe that horse cavalry, no matter how adapted to a modern role it might become, had any place on a modern battlefield. (Only the Soviet Union was to make extensive use of cavalry in World War II.) Cavalry had played no relevant role as the Great War in western Europe matured into a static set piece, and most western European cavalry organizations were disbanded to provide fillers for the attritional infantry war that dominated. Tank warfare in Poland in 1939 and western Europe in 1940 left no doubt that playing at cavalry combat on the modern battlefield was a suicide pact between horse and rider. It only remained to be seen if western cavalrymen would find a useful role for themselves, without their beloved horses.

The cavalry officer who had the greatest influence on the U.S. Cavalry modernists remained Adna Chaffee Jr., son and namesake of a cavalry general who had retired with three stars and himself a 1906 West Point graduate who loved horses and was a world-class equestrian. Chaffee served as a staff officer in France during the Great War and rose to temporary rank of colonel before coming home to resume his captaincy. He was an instructor at the Command and General Staff School and was appointed G-3 of the 1st Cavalry Division in 1921 with rank of major, attended the Army War College, and commanded a cavalry squadron from 1925 to 1927. He then served on the War Department General Staff, where he had a hand in developing army doctrine for mechanized and armored warfare (the Mechanization Study of 1928), and as head of the troop training section. Ranked lieutenant colonel and considered a mechanization visionary, Chaffee next served as executive officer of the newly transformed 1st Cavalry Regiment (Mechanized). He returned to the War Department in 1934 to serve as chief of the budget and legislative planning staff, then back to Fort Knox in 1938 to command the 1st Cavalry (Mechanized). Promoted brigadier general in November 1938, Chaffee moved up to command the 7th Cavalry Brigade, which he led in various maneuvers of the period.
 Chaffee had been marked as future general quite early in his service, and he served notably in all the important assignments that marked his career. Along the way he became the cavalry’s visionary-in-chief. Early on Chaffee saw that the cavalry needed to move from horses’ hooves to tracks and wheels, and he made the case at every opportunity, marking himself as a bore in some circles and a prophet in others. Among his favorite rants: “Mobility is needed to carry the war home, to reach the decision, to conquer. Mobility means live men arriving and establishing themselves in possession of the military objectives. To live and move quickly against the gun requires protection. Armor gives protection in movement. The gasoline engine moves armor. And so we come to what is called mechanization." And “. . . The tank is not a new weapon; the Roman legionnaire with his shield, the armored elephants of Hannibal . . . were in reality tanks using the best motive power then available."
 It can be argued that German combined-arms blitzkrieg doctrine, which married fast tanks and low-flying tactical aircraft at the forwardmost fighting front arose from the 1931 exposure of an influential German Army officer to lectures by Lieutenant Colonel Chaffee and like-minded American cavalrymen.
Chaffee’s vision, first espoused as a complete doctrine in 1927, was holistic; it foresaw the organization of a cavalry mechanized division all the way up from tank platoon to division, the interplay of swift tanks and armored-infantry, and the interplay of both with observation (but not attack) aircraft, all along the forwardmost line of battle. He foresaw the creation within each cavalry mechanized division two operational task force headquarters (combat commands in the later armored divisions) to which squadrons (cavalry battalions) and troops (cavalry companies) could be added and removed as the situation warranted. He foresaw the use of fast and unfettered mechanized cavalry as both the breakthrough force (which horse cavalry had rarely ever been) and the pursuit force (which was a traditional horse cavalry role). He saw cavalry transformed by high-powered engines and armored skins—speeded up and impervious to many forms of gunfire—in other traditional horse cavalry roles: in reconnaissance ahead of the slower infantry army, and as slashing raiders against enemy lines of supply and rear installations. He saw mechanized cavalry so swift and maneuverable that it could avoid enemy tanks and, indeed, enemy troop concentrations it could not overwhelm.


The Armor Force

After the main body of American cavalrymen had spurned a horseless modern role long enough, mechanization and armor advocates turned their backs on it, closed it off, and fought their own battles. Coming up on army maneuvers in April 1940, the army G-3, Brigadier General Frank Andrews (the ousted GHQ Air Corps commander, who had been rescued from exile by an admiring George Marshall), ordered the chief of the Cavalry Branch to transfer troops from a horse regiment to the 7th Cavalry Brigade. The cavalry chief flat-out refused, and that led Andrews to order the creation of a provisional tank brigade to be formed out of the 7th Cavalry Brigade (Mechanized) and the 6th Infantry Regiment. During the second phase of the maneuvers, the provisional tank brigade was bolstered with The Infantry School’s tank brigade. As such, this powerful large formation so thoroughly defeated the 1st Cavalry Division as to humiliate it. An after-action conference was chaired on May 25, 1940, by Andrews and attended solely by infantry and cavalry officers who favored the adoption of horseless armor commands, including General Chaffee and Colonel Patton. The gathering was unanimous in recommending the creation of an armored force separate from the cavalry branch. Shortly, Andrews conferred with Chief of Staff Marshall, and the die was cast. Mechanized cavalry units were stripped from the cavalry branch and infantry tank units were stripped from the infantry branch. Notwithstanding negative comments from the chiefs of infantry and cavalry, the plan moved forward with alacrity.
The Armored Force was created to activate two experimental armored divisions that happened to be organized pretty much along the lines Adna Chaffee had been advocating for years and had actually set down in 1939, but with the addition of an infantry regiment and a medium tank regiment per division. The Armored Force itself was stood up with Chaffee as branch chief on July 10, 1940. It was composed initially of the I Armored Corps headquarters at Fort Knox, Kentucky; the 1st and 2d Armored divisions; and a GHQ Reserve tank unit, the 70th Tank Battalion (Medium), at Fort Meade, Maryland. All these units shifted assets and personnel among themselves to make like units more or less alike.
On July 15, 1940, 1st Armored Division was activated at Fort Knox, Kentucky, and the 2d Armored Division was activated at Fort Benning, Georgia. Besides being the places at which mechanized and tank units had long been based, there is something symbolic, a setting of tone, a statement of larger intent, in the selection of the two stations, which were the home bases of the Cavalry and the Infantry branches, respectively. In October 1940, Chaffee was promoted major general, given command of I Armored Corps, and retained as chief of the Armored Force. He is still referred to as the “father of the armored force.”
Chaffee turned out to be wrong about one vital detail. For most of his tenure as mechanization visionary-in-chief emphasis in tank development had been on the tracked combat car, which was in fact another name for light tank (indeed, the M1 combat car was redesignated the M2 tank). Chaffee gave in to the infantry’s vision of a tank force whose mission it was to slow down to the speed of infantry, as the first—inherently slow—tanks had been forced to do in France. He was willing to concede a need for tanks to maneuver alongside infantry, but he wanted none but speedy light tanks in his armored divisions. The line between the light, fast maneuver tank and the heavier, slower medium tank was the capability of internal combustion engines during most of the interwar years. There was no engine durable or powerful enough to move a heavy tank fast enough to keep up with the light tanks that formed the backbone of the 1940 armored division. To be a force capable of the “slashing” cavalry-like attack contemplated by the mechanization school of thought, the Armor Force had to embrace light tanks, which were capable of moving across open terrain at 25 miles per hour. The armor and total weight of a medium tank could not be impelled across any terrain, or even along roads, faster than about 16 miles per hour, much more than the speed of marching men yet much slower than the speed of light tanks. But this was all moot in 1940. The army had not yet acquired a decent medium tank, and the obsolete and obsolescent models it did have were in short supply and thus assigned mainly to the armored divisions. In the near term, if the infantry needed tanks, it got light tanks. All this made it easy for Chaffee to concede the point to the infantry, just as long as doing so did not dent the schedule for bringing sufficient light tanks into the first two and succeeding armored divisions.
That an infantry regiment and a medium tank regiment were forced on the new armored division formation was the army’s way of getting the armor enthusiasts to take notice of the reality of battle. As fast and as dashing and slashing as tanks alone could move across a battlefield, some former enemy ground had to be held for there to be a lasting point to the exercise. Following maneuvers in 1939, Chaffee conceded the issue of what he called the “holding power” of infantry units attached to armored commands. Also, face it, tanks alone, especially light tanks alone, must go around heavily defended terrain, or woods, or fortifications, or fortified towns, or other tank-resistant obstacles, but infantry, especially infantry supported by powerful enough and highly mobile tank guns, is required to comb or reduce such impediments to tanks. That means infantry must be stitched into an armor formation. And infantry means heavier tanks with heavier guns than light tanks could bring to bear on heavy fortifications. It also means mobile infantry, which was at the time to say motorized infantry. So when the 1st Armored Division was activated, the 6th Infantry Regiment was retained as the 6th Infantry Regiment (Armored), and it became the test bed for the kind of motorization and organization that would best serve an armored division. Likewise, and with the same mission, the 41st Infantry Regiment (Armored) was activated at Fort Benning and assigned to the 2d Armored Division.
In sum, after the various points were demonstrated in maneuvers in 1939 and 1940, and in early reports concerning German medium tanks in action in France, Chaffee and his acolytes fully accepted that there was a place for medium tanks and fast-moving infantry units in the armored divisions. As a result, an infantry regiment was included in the 1st and 2d Armored divisions when they were activated up in July 1940, and specifications for one medium tank regiment per armored division was set forth in August.


Light versus Medium
Where Chaffee and his armor people went wrong was in the armament any light tank of the day was able to bring to bear on the modern battlefield. The lightly armored light tank was able to convey itself into high-speed, miles-eating battle only if it was very lightly armed—with the army’s standard antitank gun of the day, the puny 37mm. But this is understandable. As the American armored divisions were being created on paper in the wake of the German assault on Poland, a reality check would have revealed that the dominant German tank of September 1939 was the 7.2-ton, 25-mile-per-hour Panzer II light tank equipped with a 20mm main gun. Most of the U.S. Army’s 400-odd 11.6-ton, 36-mile-per-hour M2 light tanks (a 1935 design) were equipped only with machine guns, but a small number of M2A1 variants were equipped with a 37mm main gun. All the M2 variants were better armored and speedier than the Panzer II, though the Panzer II featured thicker frontal armor.
As the 1st and 2d Armored divisions were being formed, the invasion of the Low Countries and the Fall of France was spearheaded by large numbers of the thoroughly modern Panzer III, a medium tank that weighed in at 22 tons and got up to speeds between 12 miles per hour off the road and 25 miles per hour on the road. Most of the Panzer IIIs deployed in France were equipped with 37mm main guns. Thus, M2A1s and Panzer IIIs were equipped with equally powerful main guns, but the Panzer III was better armored (and its turret had been built to accommodate a 50mm main gun).
The American M2 light tank series was replaced before American armor went up against German armor, but M2A1s were deployed in the Philippines and by the Marine Corps at Guadalcanal. In 1940 and 1941 M2s adequately served I Armored Corps as a means to test tactics and tactical formations. Nevertheless, the upshot is that the American armor force foreseen by Chaffee and his fellows had fallen behind the German technological curve before it was fully activated. For all that, the follow-on M3 series of light tanks, which did see action against the Germans, was also armed with 37mm main guns.
With respect to medium tanks, the Germans for the first time fielded in France the Panzer IV, designed as a medium infantry-support tank and armed with a 75mm main gun. While the relatively few Panzer IVs deployed in France could not badly hurt the heaviest French and British tanks, they overwhelmed any light tank they encountered in relatively few tank-versus-tank confrontations. Faced with the reality of German tanks that clearly outclassed American tanks, General Chaffee had the good grace to step down from his light tank high horse and graciously accept the inevitable solution to the problem.

In mid 1940, the U.S. Army had only 60 outmoded medium tanks in hand. In development was the lightly armored M2 medium tank, which was to be armed with a 37mm gun. This was clearly a non-starter. Retaining the basic chassis design and most of its parts, the M2 was transformed into a hybrid, a medium tank dubbed M3 that was equipped with a turret-mounted 37mm gun as well as a hull-mounted sponson equipped with a low-velocity 75mm gun. The stumbling block to building a “normal” medium tank was that neither the army nor industry could yet produce a 360-degree turret large enough and inherently strong enough to accommodate the forces generated when even a medium-velocity 75mm gun was fired. The 10.5-foot-tall M3 medium tank was the worst of all worlds—a high-profile target that had to swivel on its tracks while exposing its hull in order to bring its main gun to bear. But it was technologically achievable in the short interval before the United States might be drawn into the wars in Europe and Asia. Even as the M3 medium tank was tested, revised, and first produced, the follow-on design for its successor, the M4, went ahead at full speed. The M4, only 9 feet tall, was to field a more powerful 75mm low-velocity main gun in a 360-degree turret. In any event, the first M3 medium tank pilot model was not even built until March 1941, and the first M4 pilot did not appear until September 1941.

If the 1st and 2d Armored divisions went to war against Germany in their mid-1940 configuration with their mid-1940 equipment, they were going to be defeated. But they provided hope for the future.