Monday 24 January 2022

A Sequel with Improvements

The American Heavy Tank T26E3 was standardized as the Heavy Tank M26 on March 29th, 1945. This stage was preceded by front line trials where the vehicle that the Americans spent so much time and effort building showed itself pretty well. Standardization was a green light for mass production. The end of the war limited the production volume to 2022 units, so the M26 never replaced the Medium Tank M4. It seemed that the end of production would herald in a new tank that had better armour and armament, but that was not the case. The first American post-war tank was the Medium Tank M46 or Patton, effectively a modernized M26.

Modernization instead of revolution

The Heavy Tank M26 (downgraded to a medium in 1946) was a good vehicle, but not without problems. For starters, the thicker armour still did not offer guaranteed protection from German tanks and SPGs. This could be observed in the tank's first battle, when the T26E3 nicknamed Fireball was knocked out by a Tiger tank. Essentially, the tank was protected from the 75 mm Pak 40, KwK 40, and StuK 40. Any larger gun could confidently penetrate its front armour. Another issue was the relatively low power to weight ratio, just 11.96 hp/ton even at maximum engine power. Nevertheless, the tank turned out to be rather quick (showing the highest average speed during off-road trials in the USSR), but also burned a record amount of fuel. There were also issues with the lifespan of the running gear, primarily the road wheels. These issues are rarely discussed in the context of the Second World War, but it was already present. The gumming and destruction of road wheel tired (the first one was destroyed after 753 km of driving) were also observed during trials in the USSR.

A new medium tank concept designed by the Frederick C. Brecket commission, summer of 1945. The machine guns in turret blisters were later used on the Light Tank T37.

Essentially, the Americans ended up with a good medium tank on the level of the Panther with approximately the same mobility, equal in firepower, and with somewhat less armour. The Ordnance Department, much like the Soviet GBTU, wanted a tank with a more powerful gun and tougher armour. There were projects to modernize the M26 (T26E4 and T26E5), but also more radical ideas. One such idea was presented on June 20th, 1945, by a group from the Armored Medical Research Laboratory led by Frederick C. Brecket. This work was initiated by the AGF (Army Ground Forces), who wanted a medium tank concept that weighed 40.8 metric tons, had 152 mm of frontal armour and 76 mm of side armour. How Brecket's team was supposed to fit such a tank into the prescribed weight limit was a whole separate question. There were also questions about the armament. The Americans must have been impressed by German "fishing rods" and wanted something similar in the 76 mm caliber. Brecket's concept seemed quite odd and distant from reality.

Comparison of the M26's power pack and the power pack with the Continental AV-1790 engine and CD-850 hydromechanical transmission.

Another commission's project ended in the same way. The War Department Equipment Board, better known as the "Stilwell Council", formed on November 1st, 1945. This commission could not offer anything concrete either. A tank is a combination of various components, and there was an issue with those. The most reasonable suggestion was to start with developing a new family of tank engines, since that was the weakest link at the time.

Medium Tank M26E2, a test bed for the new power pack. Despite several breakdowns, the idea proved promising.

The biggest issue was with engines for prospective heavy tanks. Existing models were used as test labs. Several engines were tested and the Americans settled on the 810 hp air cooled 29 L Continental AV-1790. This engine belonged to a family of tank engines built at Continental. Various transmissions were also tested on heavy tanks. The Alisson CD-850-1 came out on top. The combination of the Alisson transmission and Continental engine proved itself on the Heavy Tank T30. The CD-850 transmission went through several revisions to make it more reliable. The power pack turned out to be much more compact than the one used on the Heavy Tank T26E3.

The vehicle can be distinguished from a regular M26 by the mufflers, altered rear plate, and new engine deck.

This progress led to talks of modernizing the Medium Tank M26 by the spring of 1948. That was all that the American tank industry was capable of at the time. The new tank, indexed Medium Tank M26E2, was just a Medium Tank M26 with a Continental AV-1790-1 engine and CD-850-1 transmission. A prototype was converted by the Detroit Tank Arsenal and entered trials in May of 1948. This tank can be distinguished by a new exhaust system. It had two large mufflers on the fenders, which triggered a new layout of the externally stored tools. Since the engine was air cooled, the engine deck had to be reworked. The rear of the hull changed as well.

Medium Tank T40. A pilot series of 10 tanks was produced before the main Medium Tank M46.

The combination of the Continental AV-1790-1 and CD-850-1 was not an immediate success. The transmission went through several revisions. Nevertheless, trials showed that the mobility of the vehicle increased considerably, which gave hope about its future. The issue of armament was resolved separately. Experiments, including work in the M26E1, showed that a long 90 mm gun was not the optimal solution. The same conclusion was reached regarding the T98 76 mm L/70 gun. Brecket's dreams were not meant to be. As a result, the existing 90 mm gun was simply modernized. It received a new single baffle muzzle brake and a fume extractor. The new gun was indexed M3A1.

The rear of the tank changed again and a field telephone box was added.

The modernization program followed a similar path to the M26E2. The new vehicle was indexed Medium Tank T40. The Detroit Arsenal was tasked with producing a pilot batch of ten tanks, the first of which was ready in the summer of 1949. The T40 looked a lot like the M26E2, the difference was in the details. The tank received the new M3A1 gun and the improved Continental AV-1790-3 engine. The CD-850-1 transmission was later replaced with the improved CD-850-2. A small road wheel was added between the rearmost road wheel and drive sprocket. This improved the tank's performance on soft soil. A field telephone box was added on the rear. The contents of the toolboxes on the fenders also changed.

The tank with a Continental AV-1790 engine looked completely different from above.

The Medium Tank T40 pilots had a fruitful career. They were very thoroughly tested and converted for all sorts of experiments. The final vehicle was built as the T39 engineering tank. By 1948, the Ordnance Department understood that the tank should be accepted into service. The T40 was standardized as the Medium Tank M46 or Patton on July 30th, 1948.

Production and conversion

In many ways, there was no alternative to standardization of the T40 in advance of the trials. The Cold War was starting and even though the Americans had no idea what was happening behind the Iron Curtain, they quickly realized that they didn't have any new tanks. There were several solutions to this problem. The first, a revolutionary path, required "growing" a light tank into a medium one (Medium Tank T42), but this was a lengthy and risky process. There was another solution. The Americans had a whole fleet of slowly rusting M26es, and so it seemed obvious that they should be modernized. Attempts to build something better armed or better protected on the same chassis would have led to various problems. The resulting tank was not entirely satisfactory, but there was nothing better available at the time.

One of the first production Medium Tanks M46 at the Aberdeen Proving Grounds.

The minimal differences between the M26 and M46 allowed for an interesting operation. Instead of building the M46 from scratch, the M26 could be modernized to achieve the same result. This made the initial order for the M46 rather odd. 800 Medium Tanks M46 were built from scratch and 1215 more due to modernization of the existing M26 stock. This somewhat repeated the situation with the GMC M36, which was not built from scratch, but converted from the GMC M10. According to this program, more than half of M26es would turn into new more effective tanks.

The first production vehicles were put through intensive trials, much like the T40 prototypes.

Plans are one thing, and execution is another. Additional trials of the T40 had to be performed and production of the M46 slipped. The first tank only entered trials in early November of 1949. The AV-1790/DC-850 power pack continued its evolution, and so the production tanks had the Continental AV-1790-5 engines and DC-850-3 transmissions. They were more reliable, but improvements of the engine and transmission continued nevertheless. The DC-850-4 transmission with a new hydraulic drive was installed during production. More variants followed, showing that the designers kept fighting with their own transmission.

Cutaway of the M46.

The "new" tank was not too different from the Medium Tank T40. These tanks had some differences in the rear plate. The T40 had square access hatches and the M46 had round ones. The biggest difference between the M26/M26A1 and the M46 was in the running gear and engine compartment. The turret also changed. The M46 turret can be distinguished from the M26A1 and T40 ones. A rack for personal belongings on the right side disappeared. The shape of the spent casing disposal hatch changed, as well as the holders for spare track links on the left side of the turret. The T40 and M46 had a guard over the gunner's periscope, which also had a slot for a machine gun pintle mount. This was a very useful feature, since the stock pintle mount did not allow the commander to fire forward. The openings for the telescopic sight and coaxial machine gun in the gun shield received tube-shaped guards to protect them from precipitation. There were quite a few features that allow one to identify the M46 from its predecessor, even the modernized M26A1. The mass of the new tank reached 44 tons.

The M46 had a different rear hull than its predecessors. The three access hatches were round, whereas the older tanks had square ones. There were plenty of other differences, including the turret.

One event had a very large impact on the volume of production. The Korean War began on June 25th, 1950, just over half a year after production started. Because of this, the M26 and M26A1 that were earmarked for conversion were urgently needed in Korea. The modernization plans were binned. No one thought of cancelling the M46, but a superior tank was already on the horizon. Trials of the Medium Tank T42, a "grown up" T41, began in late 1950. The idea of a lighter medium tank was rejected, but the idea of installing the T42's turret on the M46 hull came up in September of 1950. This idea was standardized as the Medium Tank M47 on November 1st, 1950, and the first tanks of this type were ready by July of 1951. The M46 remained in production for just a year and a half. 1160 tanks were built and converted from the M26/M26A1.

A late production tank, likely already referred to as M46A1.

Such a rapid departure from the factories did not mean that the tank would stop evolving. The appearance of the M47 resulted in a lot of work on the M46 chassis, including installation of the Continental AV-1790-5B engine and CD-850-4 transmission, as well as improved brakes, firefighting equipment, and oil system cooling. All of these features were put into production in 1951. Since the internals of the early and late tanks were different, the improved version was renamed to Medium Tank M46A1 in April of 1951. Externally the M46 and M46A1 were identical. 360 of these "intermediate" tanks were built.

Fast but unreliable

The Medium Tank M46 was the least lucky of the Pershing/Patton family. Only 1160 units were built, much less than any other tank from the family (excluding the Medium Tank M45, which was merely an M26 with a 105 mm howitzer). The revolutionary engine of the M46 led to problems. This tank was the first of a whole series of tanks that used the new family of engines, and pioneers often end up with the most growing pains.

M46 disembarking in Korea. This war was the cause of biggest turns of bad luck for the Patton.

The Korean War turned out to be a bad turn for the M46's career. If it never happened, the tank would have had a different fate. At the very least, there would not have been a need for the hybrid tank with the M46 chassis and T42 turret. The urgent shipment of tanks that only entered service in late 1949 to Korea had a very negative effect on the tank's reputation. A tank needs a year or two of service to iron out all the bugs, but the Patton never had that luxury, and so the tank was sent to Korea as is. The first tanks of this type issued to the 6th Tank Battalion landed in Korea on August 8th, 1950. About 200 tanks arrived by the end of the year. At first, the Pattons did not see any T-34-85 tanks, nor was their mobility advantage used fully. The most common American tank at the time was still the M4A3E8. It was quite mobile and had a high reputation among American tankers.

M46 from the 1st USMC Division.

The Patton only saw real combat starting in November of 1950. The tanks were successful at first, until the Chinese volunteers began their offensive. The front lines were rapidly moving up to China's borders, but started to roll back just as quickly. The front lines did not just catch up with the 6th battalion, but overtook it. As a result, a number of these tanks were captured at Pyongyang while still loaded on a train. It is often written that the tanks were all destroyed by aircraft, but that is not the case. A number of vehicles were recovered, likely including the one that ended up in the USSR in 1951. The tank was shipped to Kubinka, where it was thoroughly studied. Soviet specialists were most interested in the CD-850-3 transmission.

A tank from the 6th Tank Battalion that ended up in Kubinka in 1951, remaining there to this day.

The idea of building a Soviet hydromechanical transmission was born in 1951. It was later tested on the Object 266 tank, a converted Object 730. The tank was left at the proving grounds after the trials finished. Today, both the M46 and the Object 266 can be seen at the Kubinka museum.

Diagram of the M46 tank's transmission. This was the most interesting part of the American vehicle for Soviet specialists. An equivalent system was later tested on the Object 266 tank.

The situation with the Patton was somewhat comical. This tank had high mobility and was supposed to fight in the vanguard of American troops in Korea, causing fear among North Korean tankers. In reality, these tanks destroyed fewer than two dozen T-34-85 in their entire career, losing 8 vehicles irreparably to enemy fire. The biggest issue was not enemy tanks. The Patton's main enemy was itself. 60% of losses were taken due to mechanical failure. A more powerful engine also meant higher fuel expenditure. As mentioned above, the M26 set a record in fuel consumption among in its class, and its successor beat that record once more. By official numbers, the tank's 878 L fuel capacity was enough to drive just 130 km on roads.

The M46 in tiger camo were the most famous tanks of the Korean War. These were good looking vehicles, but their combat effectiveness was more questionable.

Most vehicles were converted during service. One of the most famous conversions was the spotlight tank used by the 1st USMC Division. A 457 mm spotlight was attached to the gun mantlet. These tanks were used for night combat. There were a few variants of these conversions. The most brutal looking conversion was no doubt the engineering tank on the M46 chassis. It was equipped with a bulldozer blade and protective netting around the turret.

One of the variants of 18 inch spotlight installation on the M46.

The result of the tank's service in the Korean War was disappointing. It did not reveal the full potential of its engine. The crews were left with a poor impression, namely low reliability and high fuel consumption. By the end of the war the army already had the improved M47 and the M48 loomed on the horizon. The M46 was not in demand as a result. It was officially removed from service on February 14th, 1957. The M4A3E8 that proved itself a reliable workhorse in Korea was retired at the same time.

An engineering tank equipped with a bulldozer blade and protective netting around the turret.

This was not the end of the M46's service. Like the Pershing, the tank was used by other nations. Naturally, South Korea was one of its users. A few vehicles were sent to France in 1954. The M47 was already coming, so the M46 was out of luck here too. 8 tanks were issued to Belgium. Finally, some sources claim that the M46 was used in the Italian army, but that is not the case. The Italians may have considered the M46, but by 1952 they were allocated 143 M47 tanks by the MAP (Mutual Assistance Program). The M46 was not needed here either.

The Korean War was the only highlight of the M46's career. The tank was unlucky. The start of the war did not allow it to be built in large numbers or give it time to iron out bugs.

Retirement didn't treat these tanks well. 75 Pershings survive to this day, but only 21 M46 Pattons. The Korean War was the only conflict in which it was used. This war was, in many ways, responsible for the tank's disappointing career.

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