Battles for Seoul
The Patton Tank, Part One
By Arrigo Velicogna, Ph.D.
June 2020

The Patton medium tank family, spanning four models, M-46, M-47, M-48, and M-60, represents one of the most enduring efforts of the US tank industry to cope with changing battlefield conditions, strategic imperatives, and political constraints. Patton tanks fought in almost every Cold War conflict and beyond, under different flags. They also witnessed the transition between medium and main battle tanks. Like the Soviet T-55 and the British Centurion, Patton tanks were a Cold War icon.

Yet, at a close examination, the Patton family is less of a close-knit family than a group of designs sharing some common characteristics and a name. The M-46 Patton of the Korean War was completely different form the M-60A3 Patton still serving today. Calling them part of the same family could be a stretch. Basically, every medium tank between the WW2 M4 Sherman and the M1 generation was named Patton. While a stretch certainly there was a reason for that continuity in name, a reason that, hopefully, this brief history of the Patton tanks will clarify.

Out with the old… back with the old… the M46 Patton
In September 1945, with the surrender of Japan, the US Army found itself with four tanks models in its inventory. In the light department the M5 family was being phased out and replaced with the M-24. The medium tank slot was filled by the M4 Sherman, with production and standardization now focusing on the latest variant, the M4A3E8. The heavy category was represented by the M-26 Pershing, a tank that suffered from a troubled birth and had been deployed in insignificant number. Less than 20 Pershings effectively saw combat.

All of these tanks had strength and weaknesses. The M-24, M4, and M-26 appeared to have still room for improvements. With the customary drawdowns that followed each United States’ war four different tank models were redundant. To appease a Congress that wanted to benefit from victory as soon as possible, and a President that had not yet committed himself to a confrontation with the Soviet Union for hegemony over the post-war world, streamlining, if not outright chopping, was the order of the day.

A Marine loads a Pershing’s machine gun in Korea, July 1953.

If streamlining was indeed imperative, Army doctrine in 1945 was still predicated on three different categories of tanks: Light, Medium, and Heavy. This approach had been reaffirmed by the Army Ground Forces Review Board in January 1945. The Board recommended developing new families of light, medium, and heavy tanks of 35, 45 and 75 tons respectively. It is also worth to note that the same board also recommended the study of a super heavy tank in the 150 tons class. Streamlining would thus follow these three pillars.

At the end of 1945 the US Army standardized its light fleet on the M-24, and its medium fleet on the Pershing, declassing it from heavy to medium. It was not altogether a radical move. The Pershing represented a newer generation of mediums compared to the Sherman, and its firepower and armor compared well with the next generations of medium tanks coming from the other tank-building nations, basically the United Kingdom and the Soviet Union. With a 90mm gun and a frontal armor of 102mm the Pershing was basically a sound design, but it was handicapped by having retained the same powerplant of the M4 Sherman on a heavier hull. It was hopelessly underpowered. As it would become evident in Korea, Shermans were better climbers and cross-country riders than Pershings.

The US Army was aware of the issues and had already studied remedies. A project to improve the Pershing’s power-to-weight ratio had been launched in 1946, but it competed for scarce funding with other priorities, including designing a new generation of tanks. In January 1946 the Stilwell Board, an Army study group chaired by Lieutenant General Joseph “Vinegar Joe” Stillwell of Burma fame, had recommended a new tank program focused on three models, a 25-ton light tank, a 45-ton medium, and a 75-ton heavy, reprising the recommendations of the previous AFG board. The Stillwell board rejected the recommendation for a super-heavy tank over 100 tons. More importantly the Board also recommended the development of dedicated technology for tanks, in the form of dedicated guns (rather than converted field artillery, naval guns, or anti-aircraft pieced), range finding equipment, and engines. Yet recommendations were one thing, reality was another.

The Stillwell Board’s conclusion notwithstanding, the supreme Army leadership, in the person of General Omar N. Bradley, was not supporting tank developments. Bradley appeared to have been an early convert to the atomic revolution, going to state that the role of the Army would be “to support the strategic air offensive. Our main job would be to protect air bases at home and abroad.” A similar view would be held by Bradley’s replacement as US Army Chief of Staff, Lawton J. Collins. Thus, the re-engineering of the M26 became a low priority item. As Philip Bolté and Stephen Taaffe argued in their recent works, Bradley and Collins wholehearted embrace of atomic weapons was both misplaced and bound to cost the Army dearly. The net result was an US Army starved of funds.

A Pershing taken by the People’s Liberation Army in Korea.

On the other hand, the international situation evolved in a way that was to save the tank from the atomic oblivion to which charlatans had already consigned it. Far from reaping peace dividends, the United States was heading toward a multi-decade confrontation with the Soviet Union. While the 40 years of the Cold War were not destined to witness massed tank battles between the Soviet and the US armies, tanks would play a critical role. When President Truman took the fateful decision to face Soviet aggression, he looked at the US Army tank parks, US Army top leadership notwithstanding. What the former artillery colonel saw was not encouraging. In 1948 the US tank inventory was impressive, on paper, with thousands of tanks, but was a hollow inventory. The size of the army was 552,000 men. Yet only one armored combat command (brigade size) was available in the strategic reserve. Forward-deployed infantry divisions in Germany and Japan were desperately short of tanks. There were no operational armored divisions stateside, either. Tanks were mainly in storage rather than operational. Despite the decision to standardize on the M-26, forward-deployed units in Germany and Japan fielded only M-24 light tanks, mainly for cost reasons. Around two thousand M-26’s were in the States, or in storage in other countries, in various state of readiness. Both the M-26 improvements and the new tanks recommended by the Stilwell Board were languishing due lack of funding, only the light tank proposal being pushed forward. Emergency measures had to be taken.

While a new generation of tanks was the ideal solution, what could be done to redress the situation on the spot was to accelerate the work on improving the Pershing. Two important elements had surfaced in the program. The first was the new Continental AV-1790A-3 engine, rated for 810 gross HP. It represented a massive improvement over the original Ford GAF and its 500 HP. The second critical element was the Allison CD-850-1 Cross Drive automatic transmission. An automatic transmission had been a chimera for the entire development process of the Pershing, causing constant troubles for the tank and frictions between Ordnance, Army Ground Forces, and the Armored Branch. Now a reliable automatic transmission was available. Not only did it improve cross-country capability and allow the tank to pivot on its length, but it immensely eased drivers’ workload. Instead of having to rely on physical strength to operate the two lateral levers the driver now used an easily controlled “wobble stick.” Borrowing today’s buzzwords, it was a “game changer,” at least for drivers. While work on both had started in 1943, they did not reach maturity before the end of 1945. They had missed the war, but were now available for use.

The new engine and transmission were successfully tested in a Pershing tank in 1948. The resulting vehicle being initially labelled M26E2. Fitting the new engine and transmission to the M26 required minor modifications. In addition, a new 90mm gun was tested, as well a new 3-inch gun, a copy of the US Navy’s new 3-inch antiaircraft gun. But in an Army starved for funds, non-essential modifications had to be dropped so the standard 90mm gun of the Pershing was retained, with the addition of a new bore evacuator and a slightly modified muzzle brake. While the M26E2 was perfected, a new version of the Continental Engine and Allison transmissions were developed. Ten test tanks with the new Continental AV1790A-3 engine coupled with an Allison CD-850-1 Cross Drive were ordered for testing purposes. Armor and firepower were left untouched from the previous trials. Installing the newest Allison engine required modification to the rear deck of the Pershing. The new powerpack needed plenty of air and the new hull sported new armored grills on the rear deck, a feature that would remain on the following members of the Patton family. The last visible modification was the addition of an idler between the last road wheel and the drive sprocket. Yet the conversion effort was minimal compared to the design effort of a new medium tank. The new vehicle was designated T40, and then accepted into service as M-46 on 30 July 1948 and named the Patton, in honor of Lieutenant General George C. Patton Jr., while the first T-40 was still on the assembly line.

The first test vehicle (T-40) was delivered from the Detroit Tank Plant to Aberdeen Proving Ground on 2 August 1949, quickly followed by the rest of the tranche, with the exception of the number 10 prototype that remained at Detroit for conversion to an engineer vehicle. Testing at Aberdeen was positive and the M46 worked well. Its new power pack markedly improved cross-country performance and even allowed the tank to pivot on itself. The main drawback of the Pershing was thus eliminated.

An M46 Patton in Korea.

The US Army had intended to declare the M26 obsolete and replace it wholesale with the new M46, but the idea had several problems. The M46 was to be obtained by conversion from existing M26s. No new production was envisaged both on cost grounds, and on the fact that the M26 was considered an old design already approaching the end of its growth potential. Thus, the US Army planned to literally rework its fleet of M26s to M46s on an almost one to one basis. Available funding and production capacity slowed the process compared to Army’s wishes. The 1949’s budget allocated funding only to the conversion of 800 M46’s. A further 1215 M26’s were allocated for conversion in 1950, pending available funding in the following year. The slow process meant that units would still have to field Pershing tanks and to maintain them, thus requiring spare parts. Designating the M26 as obsolete would have cut the flow of spares. The solution was found in declaring the Pershing a limited standard continuing its operations and maintenance. However, allocation of M26 tanks to operational units required a special authorization from the Department of Defense. While the worsening of the international situation, and especially the Soviet blockade of Berlin in 1948, had forced the US government to reassess its priorities, defense outlook, and military preparedness, funding was still scarce.

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