Monday, 19 October 2020

Just Add Armour

 The caleidoscope of various vehicles based on the Heavy Tank T26E3 shows how difficult the situation was with American heavy tanks. The T26E3 was really a medium tank, especially when it came to armour. Several variants were developed to make it into a true heavy, from installing more powerful armament to a thorough modernization that resulted in the Heavy Tank T32. The simplest variant was the Heavy Tank T26E5 where the designers decided to limit themselves to thickening the tank's armour.

Never enough

American medium tanks inevitably gained armour as they evolved. The Medium Tank T20 had just 64 mm of front armour in the hull and 89 mm in the turret. With the T26E3 this armour increased to 102 mm. This was more than most medium tanks of the period, but with the caveat that the cast armour had lower toughness than rolled. However, the T26 was moved to the heavy tank class in the summer of 1944 entirely due to its growing mass. In reality it was still a medium tank, albeit from a new generation. Protection didn't magically increase when its designation changed, but as the evolution of the Heavy Tank T29 and Heavy Tank T30 later showed, American generals considered 102 mm of front armour sufficient for a heavy tank.

A Heavy Tank T26E3 disabled on March 1st, 1945. Two HE shells destroyed the running gear and knocked off the commander's cupola.

German tanks and their guns didn't share that sentiment. It's almost as though the Americans ignored the presence of the Tiger tank. Meanwhile, the Soviet GABTU clearly indicated that at least 120 mm of front armour was needed to protect against the 88 mm AA gun (which the 8.8 cm KwK 36 L/56 was derived from) back in 1941. As trials held in 1943 showed, the Tiger's gun could penetrate the KV-1's 95 mm of armour from 1.5 km. It's no coincidence that first the KV-13 and then the IS tanks had 120 mm of front armour. Practice showed that the Tiger's gun wasn't even the most dangerous opponent. That would be the Panther's 75 mm KwK 42 L/70 which had higher penetration. Losses of IS-1 tanks in battle against them resulted in development of the modernized IS-2. As for the Americans, they expected that the war would be won with the Medium Tank M4 and thus even the debut of the T26E3 was fairly late. This was the cause of an unpleasant experience when fighting Panthers in the summer of 1944. The debut (however unsuccessful) of the Tiger II tanks also left a mark. Even though it was the British and not the Americans who ran into them first, this threat was evaluated very quickly. Work on new heavy tanks that could fight the Tiger II began in August of 1944.

Fighting in the fall of 1944 showed that the M4A3E2 assault tank was better protected than the Heavy Tank T26E3, which hadn't even made it to the front. This resulted in the creation of a reinforced version of the tank.

The main issue was that even urgent development of a heavy tank would not give a new vehicle in time. As a result, less ambitious but more achievable projects were developed in parallel. An experimental Heavy Tank T26E1 was equipped with a more powerful T15E1 gun in January of 1945. This tank was renamed Heavy Tank T26E4 and sent to the front lines where it even saw battle a few times. However, this tank only had improved armament, not protection. Sure, the tank received applique armour, but this was an improvisation that had a severe negative effect on its characteristics. The issue of armour had to be solved in factory conditions. The Americans already had experience with this. The Medium Tank M4A3E2, a special assault variant of the M4A3, went through this process. The mass of the tank grew to 38 tons, but the thickness of the front hull increased to 102-140 mm and the turret to 152-178 mm. The use of these tanks in the fall-winter of 1944 showed that this was a worthwhile tradeoff. The M4A3E2 tanks were seldom penetrated, even though they typically led the column and got hit more than other tanks. 

The first Heavy Tank T26E5 prototype, Aberdeen Proving Grounds.

The success of the M4A3E2 triggered analogous improvements to the Heavy Tank T26E3. The question of a "thick-skinned" T26E3 was first raised on December 7th, 1944. According to initial requirements, the hull was thickened to 121 mm and the turret to 203 mm. Four tanks indexed Heavy Tank T26E5 were planned initially, but the results of front line encounters increased this requirement. On January 12th, 1945, the Ordnance Committee recommended production of ten tanks. It was abundantly clear that increasing the armour will result in a decreased mobility, so two vehicles were approved: a major and a minor redesign. The major redesign turned into the Heavy Tank T32, essentially a whole new vehicle which was better protected but needed more time to be developed. The alternative didn't need a new engine and could be put into service much faster.

Protection like on the Tiger II

Ground Forces requested that the armour of the T26E3 be increased to the level of the M4A3E2 on December 7th, 1944, but this was going to be difficult. The T26E3 already weighed 42 tons and even the most optimistic calculations indicated that its mass would rise to 44 tons. T80E3 tracks with extensions would be used to compensate for the mass, increasing the track width to 711 mm. This caused issues when transporting the tank by rail. The T26E3 was 3513 mm wide, the T26E5 was 3759 mm wide. This was too wide for railroads and the fenders would have to be partially removed for transport.

Turret of the Heavy Tank T26E5. The numbers show how the thickness of the turret armour changes from the front to the rear.

It is said that appetite grows with the meal. When documentation for the up-armoured T26E3 was presented in early 1945, the army no longer considered it enough. This point of view was justified. The initial plan was to protect the tank from the 88 mm KwK 36 L/56 and 7.5 cm KwK 42 L/72. However, these were not the most powerful guns in the German arsenal. The Tiger II with the 88 mm KwK 43 L/71 was used quite extensively during the German counteroffensive in the Ardennes, and this tank's gun could easily penetrate even the improved American tank from medium ranges. This was as also installed on German tank destroyers such as the Nashorn and Jagdpanther, which were encountered quite often. The idea to increase the armour even further was solid.

The gun mantlet was inspired by late model Panthers.

The Ordnance Committee increased the size of the pilot batch to 27 vehicles on March 29th, 1945. The requirements for protection were also revised. They put it bluntly: the army wanted protection on the level of the Tiger II. Instead of 121 mm the front hull was now 152 mm thick, about the same as the Tiger II. The turret front was even thicker at 191 mm and the mantlet was a whopping 279 mm thick. The tank would be completely immune to the 88 mm Pak 43 from the front. Of course, the mass would increase drastically, but this seemed like the only correct solution.

A Heavy Tank T26E5 at the Aberdeen Proving Grounds, July 1945. The results of the trials were mixed.

The war was still not over, so the task had to be carried out as quickly as possible. Not much time remained for the conversion, especially since the design was ready only by mid-March and approved by the Ordnance Committee on March 29th. The designers didn't reinvent the wheel and took the same path as with the M4A3E2. Like the M4A3E2 turret, the T26E5's turret front grew in thickness by more than 1.5 times. This was the largest increase, but the armour was thickened all around. In the thinnest place the sides were 89 mm thick and the thickness of the rear was increased from 76 to 127 mm. This was the only way to prevent the center of mass from shifting forward too much.

The "heavy Pershing" didn't look too different from its predecessor from a distance.

The shape of the turret didn't change much, but the same can't be said for the gun mantlet. American designers kept track of foreign developments, even enemy ones. One of them was the improved gun mantlet of the Panther Ausf.G. Initially the mantlet was curved, but combat results showed that enemy shells often ricocheted into the fighting compartment roof. A gun mantlet with a prominent "chin" was developed to prevent this. A similar design was used on the T26E5: curved on the top and flat on the bottom. There still had to be a slope to preserve a reasonable gun depression angle.

The tank was more distinctive from the back.

The gun mount had to change in connection with the new turret and mantlet. The recoil mechanism springs were strengthened. The counterweight was also increased. Unlike with the T26E4 the amount of changes was not great, as the weight did not increase that much. The designation of the gun mount remained the same: M67.

Unlike the turret, the shape of the hull didn't change.

The changes to the hull were nearly imperceptible. This was pointed out in supporting documentation. Designers complained that due to the rush there was not enough time to thoroughly work on the front hull. The armour thickness increased to 152 mm in some parts and 203 mm in others. Such a radical increase was partially connected with the elements that couldn't be radically reworked, such as the bulge for the driver's compartment ventilation fan. As a result, the tank's frontal protection was somewhat less than that of the Tiger II. In addition to the front hull, the turret ring splash protection was thickened from the front. This meant that the driver's hatch had to be shortened.

The tracks received extensions to keep ground pressure at a reasonable level.

The mass inevitably increased to 45.8 tons. Since the engine was not changed the power to weight ratio dropped to 10.9 hp/ton. Considering that the T26E4 weighed 50 tons with its front line tuning, this was not such a large increase. The ground pressure was acceptable due to track extensions. The main clutch had to be strengthened due to the greater mass.

It's easiest to distinguish the T26E5 from above. Like the M4A3E2, the turret front is much thicker.

The Heavy Tank T26E5 project was finally approved on in early May of 1945. Production began at the Detroit Tank Arsenal in June and the batch of 27 tanks was finished in August. The final version of the tank weighed 46.4 tons and the power to weight ratio dropped to 10.78 hp/ton. No further orders followed. The war in Europe was over and the tank still had to be put through trials. Nevertheless, the T26E5 was the most numerous among the next generation of American heavy tanks. This tank could be called a heavy without any asterisks. Its protection and weight were fully on par with other representatives of this class.

Mobility is more important

The first trials began in mid-June of 1945 at the Detroit Arsenal. Surviving correspondence between the Ordnance Department and Aberdeen Proving Grounds indicates that the Americans were starting to suspect something. Some concerns about the tanks's suspension were voiced when it turned out that the actual mass was greater than expected. Even the T26E3, which was already standardized as the Heavy Tank M26, had issues with its suspension. With the T26E5 this issue was only exacerbated. It was also mentioned that special attention must be paid to the gun mount, as it was also altered.

One of the Heavy Tanks T26E5 at Fort Knox. Note that this tank does not have track extenders.

Even though delivery of the tank with registration number U.S.A. 30150824 and serial number 10007 was planned on June 20th, 1945, in practice the tank only arrived in July. That is when mobility trials began. Specifications approved in May of 1945 set the top speed at 36 kph, but this was a very optimistic requirement. In practice the tank could reach 32 kph on a highway, although a speed of 40 kph could be briefly reached if the engine worked at maximum RPM. This is the not worst result for a heavy tank, but the Americans required high mobility even from heavy vehicles.

The thickened right turret cheek can be seen from the front.

The top speed was only one parameter of the trials. Trials showed that the concerns about the suspension were not without merit. The increased load on the front road wheels had unpleasant consequences. It was not just the suspension elements that suffered, but also the road wheel tires. This further decreased the T26E5's chances at mass production.

Trials of tank with serial number 10009 also ended poorly. After the war the Americans came to the conclusion that mobility is more important for a tank than thick armour.

Gunnery trials were another factor that put an end to the tank's career. Even though the gun mount was strengthened there were still issues that were never solved. The effort required to operate the elevation flywheel increased. The heavier turret impacted its rotation speed. The hydraulic traverse made a full rotation in 20 seconds (compared to the M26's 15 seconds). One can imagine how hard it was to traverse by hand. The results of proving grounds trials were far from ideal.

Aberdeen Proving Grounds, February 1949. This tank was scrapped a few years later.

Another tank (registration number U.S.A. 30150826 serial number 10009) was sent to Fort Knox for army trials. These trials also ended poorly. The reduction in mobility of the tank and its gun and decrease in reliability was far from what the Americans wanted. The M26 was considered satisfactory in comparison, especially since it was reclassified as a medium tank and work began to improve its mobility. This resulted in the creation of the Medium Tank M46, which had the same armour as the M26 but with higher mobility. The Heavy Tank T26E5 turned out to be not needed. These tanks suffered an unfortunate fate: even though 27 were built, not a single T26E5 survived to this day.

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