Saturday, 14 March 2020

Pershing on Steroids

The history of the American heavy tank building program during the years of WW2 is very messy. On one hand, there was a standardized Heavy Tank M6, which quickly became obsolete. On the other hand, a whole three heavy tanks were in development by the spring of 1945. The first, the Heavy Tank T28, had little resemblance to a tank. The second, the Heavy Tank T29, was the highest priority. Finally, the Heavy Tank T32, the development of which began later than all the rest, was built a year and a half earlier than the T29. Even though the tank was just an "overfed" M26 Pershing, it ended up as the best protected American classic heavy tank built in the 1940s.

The fourth way

American tank building actively evolved in 1943, but stagnated by early 1944. One of the reasons was the unfortunate end of the T23. The tank was a radical leap forward, surpassing the Medium Tank M4 in every way. The problem was that military trials ended in an unpredictable way. The electromechanical transmission that was used on tanks of this type ended up causing many headaches, especially in those who had to service it in the field. As a result, even though 248 tanks of this type were produced, it was not accepted into service.

The only good thing to come out of the Medium Tank T23 program was the new turret, which had the same turret ring diameter as the Medium Tank M4, which brought about the M4A1(76)W, M4A2(76)W, and M4A3(76)W. These were the best American tanks of the war that were mass produced. The T23 tank program was not abandoned entirely. Further development led to the creation of the Heavy Tank T26E3 (also the Medium Tank M26).

A draft of the Heavy Tank T32, 1945.

The second cause of the crisis that struck in the summer of 1944 was the neglect that American command treated heavy tanks with. The M6 program developed successfully, but experience in North Africa showed that American tank units needed mobile vehicles. The Heavy Tank M6 was not exceptionally mobile, and the weight of nearly 60 tons made it complicated to move by rail. As a result, development of heavy tanks first stalled and then ended entirely. Instead of the Heavy Tank M6, development of the Heavy Tank T28 began in September of 1943. It was initially based on the experience of the M6, but the T28 looked more like an SPG than a tank. Work on the T28 progressed slowly and changes were constant. It seemed that the program only continued for the sake of optics. American generals considered the Medium Tank M4 and Gun Motor Carriage M10 sufficient for this war.

This was the case for a time, but in the summer of 1944 a cost was paid in the lives of American tank crews. Normandy was the first place where American tanks first encountered a large amount of Panthers. Unlike in movies, where the Americans face a large amount of Tigers, they did not meet them in Normandy. Panthers, on the other hand, were very common, and potentially much worse foes. The Panther was much better protected from the front and its cannon could destroy American tanks from a great distance.

The tank had the same 90 mm T15E2 gun as the T26E4.

The most unfortunate surprise was the appearance of the Tiger II tank in mid-July of 1944. The Americans did not face these in Normandy either, but it was clear that such a meeting would happen before too long. This triggered the launch of the Heavy Tank M6A2E1 program in the summer of 1944, but it did not last long. The M6A2E1 program was classified as auxiliary in the development of another tank: the Heavy Tank T29. The second direction was the T28, which had its requirements change again. The third direction was the improvement of the Heavy Tank T26. This was the only direction that had any results before the end of the war in Europe. The result of this program was the Heavy Tank T26E4, a prototype of which fought in the 3rd Armored Division.

Ammunition for the 90 mm T15 gun. Considering that the dimensions of the turret were the same as on the T26, one can hardly be envious of the loader's work.

The development of a "Pershing with a long arm" split up into two, and then three different directions. The cause of this was insufficient protection of the tank. 102 mm of armour was not enough to protect against the Tiger's gun, let alone the Panther's. The Nashorn was also a potential foe: one T26E3 was destroyed by this tank destroyer. On the other hand, there was already an American tank with sufficient protection available. The Medium Tank M4A3E2 with a 100-140 mm thick hull and 178 mm thick turret was penetrated very rarely. An idea occurred to boost the frontal protection of the Heavy Tank T26E3.

Officially, the protection improvement program began on December 7th, 1944. However, the question of how the chassis will deal with the increased load cropped up very quickly. Increasing armour alone likely would not have been enough. For this reason, the Ordnance Committee recommended the development of a second variant of the thickly armoured Heavy Tank T26E3. This would be a very thorough modernization, closer to a completely new tank on the Heavy Tank T26 chassis. The new tank would be a heavy through and through.

Ultra-Pershing

Officially, work on the new tank, indexed Heavy Tank T32, began in March of 1945, but in practice development began earlier. This was an intermediate link between the Heavy Tank T26E3 and the much heavier T29. Assemblies from the T26E3 were used as much as possible during development, but the Ordnance Department understood that improving the armour and armament any further would not be simple. A significant increase in mass with the same hull and running gear would result in overloading, which was already observed on the T26E4. The chassis required serious improvements. The hull was lengthened to 7071 mm, which meant that the number of road wheels increased to 7 per side. A more powerful engine was also needed, since the 500 hp Ford GAF was clearly not enough. A 770 hp 12-cylinder variant, indexed Ford GAC, was selected.

The first prototype of the Heavy Tank T32, Detroit Arsenal, January 1946.

According to the correspondence of the Ordnance Committee, four prototypes of the Heavy Tank T32 would be built. Due to the widespread use of T26E3 components, these tanks could be developed and built in a short time. A model of the new vehicle was ready by April 10th, 1945, in addition to 80% of the blueprints for two of the prototypes. The Detroit Arsenal, one of the producers of the T26E3, would also built these tanks.

This high speed of development would not last for long. The end of the war in Europe led to a review of most prospective projects. The Heavy Tank T32 was no exception. The order for 4 prototypes was not cancelled, but the order was no longer urgent. The concept also changed. The Heavy Tank T26E3 showed in Europe that cast frontal armour was not robust enough. As a result, the Ordnance Committee ordered on August 9th, 1945, that the third and fourth prototype T32 would be built with rolled front hull armour. These tanks received a different index: Heavy Tank T32E1.

The same tank from the front.

The first two prototypes of the Heavy Tank T32 were ready by January 15th, 1946, less than a month after the first Heavy Tank T28 (T95) was built. Even though these tanks came too late to take part in the war, they were the most thoroughly developed of all American experimental heavy tanks. They were also the lightest. The Heavy Tank T32 weighed 54,431 kg. The more powerful engine gave it a power to weight ratio of 14.1 hp/ton. To compare, the Heavy Tank T26E3 had 11.9 hp/ton.

The running gear was generally the same as the Heavy Tank T26E3 had, but the hull changed significantly. The front armour was increased to 127 mm at a 56 degree slope, which gave reliable protection from the 88 mm Pak 43 at all ranges. The thickness of the lower front armour was 95 mm at 59 degrees. This armour could be penetrated, but only at close ranges, and would be very difficult to hit. The front armour retained one aspect that made it much easier to penetrate: the hull machine gun.

As the height of the tank remained nearly the same, the Heavy Tank T32 looked much more squat than other American heavy tanks.

The rear of the vehicle also changed greatly. Its engine was not just more powerful, but longer, and the engine compartment had to be lengthened. The transmission changed as well. Instead of the Torqmatic Model 900-T with a torque converter, the Heavy Tank T32 used an EX-120 transmission developed by General Motors. Thanks to a gearbox with perpendicular gears, the transmission was very compact, but the rear of the tank had to be changed due to increased width. The exhaust system changed too. The tank received two massive mufflers that flanked the engine compartment. The engine deck was changed, and the fuel tanks were relocated.

View from above. The increased thickness of the turret armour is obvious from this angle.

Unlike the hull, the turret was not changed as drastically, at least at first glance. The overall layout remained the same as on the Heavy Tank T26E3, and only the 90 mm T15E2 and massive gun mantlet hinted that something changed. The rear of the turret was also altered. Since the gun was much longer, a counterweight was added, which was combined with the new air intake. In reality, the turret was much different than it seemed. The gun mantlet was 298 mm thick, which was a record for American tanks with rotating turrets. The thickness of the sides was 152 to 197 mm, the rear was 152 mm thick. The turret of the Heavy Tank T32 was the best protected of all American heavy tanks of the 1940s. The gun was installed in the T119 gun mount, the same as the Heavy Tank T26E4 had.

EX-120 engine/transmission assembly, the Achilles' heel of the tank.

Such a radical increase in armour and the longer gun had a significant effect on the suspension load, especially in the front of the tank. The hull was not just lengthened to give the engine more room, but to move the turret. It was shifted back slightly to even out the load. However, the larger fighting compartment did not mean that the tank would carry more ammunition. The Heavy Tank T32 carried 54 rounds. The problem was not in casings that were too long, even the shift to separate loading did not resolve this issue.

Heavy Tank T29 and Heavy Tank T32 at the Detroit Arsenal. The difference in height and different design of the hull can be seen.

The first and second Heavy Tank T32 prototypes received the registration numbers U.S.A. 30162828 and U.S.A. 30162829. The first Heavy Tank T32E1 was finished on May 14th, 1946, and the second was finished on June 19th. They did not differ from the T32 in anything but the front armour. The use of rolled armour and removal of the hull machine gun gave them superior protection, but it did not matter anymore.

Neither fish nor meat

Both Heavy Tanks T32 arrived at the Aberdeen Proving Grounds on April 19th, 1946. By then, the fate of the American heavy tanks was sealed. Mass production was no longer considered. The T32, as with other heavy tanks, would play the role of a mobile testing lab. Components and assemblies that would later be used in other prospective tanks could be tested in this way.

The second experimental Heavy Tank T32 at the Aberdeen Proving Grounds, late 1946.

Strangely enough, the T32 was the least interesting of all the heavy tanks for the Americans. The cause of this was the gun. The 90 mm T15E2 was considered weak. It had the same parameters as the German 88 mm Pak 43, which this tank was completely proof against frontally. More powerful 105 mm guns did not fit into the T32. However, even the 105 mm T5E1 gun that was used in the T29 was not powerful enough. As trials against the Tiger II showed, the T5E1 could not penetrate it from the front, and neither could the 90 mm "fishing rod".

The height of the T32 was 2810 mm to the top of the commander's cupola, not much for an American heavy tank.

The only thing that the T32 was good for was reliability trials. These trials were very important, as the Heavy Tank T29 used the same transmission and engine. While the engine worked fine, the EX-120 transmission was a real headache. The transmission on both tanks broke down regularly. It also turned out that it was difficult to service. The electromechanical transmission was the last nail in the T32's coffin. However, there was another side to that coin. After all of these trials, the Alisson company developed the CD-850-1 hydromechanical transmission. It was used on the T29, T30, and T34 tanks. After improvements, the CD0850 was used on the M46 tank. A whole series of tanks later received this transmission, including the M103, the only American heavy tank to be built in large numbers.

The same tank from the back. The hull and turret are very different from the T26E3.

The second prototype of the Heavy Tank T32E1 remained at the Detroit Arsenal, where it was used as a test bench. As for the first one, it was sent to Fort Knox. It went through trials there, which turned out to be just as torturous as the ones held at Aberdeen. The same problems observed when testing the Heavy Tank T26E4 repeated themselves. The long barrel was very inconvenient when driving, as there was a significant risk of hitting the ground with it. Issues with the loader's station did not disappear either. Even separate loading didn't help. The only advantage of the T32 over its "big headed" brothers was improved off-road performance, which was a little bit of ointment on a huge fly. 

The inside of the fighting compartment.

Unlike other American heavy tanks, which are still represented by at least one survivor, not a single Heavy Tank T32 remains until this day. This is a sad and disappointing finale for a tank that could have seen mass production had the war taken a year longer. Comparing the T32 and T29, the "odd one out" seems much better than the tank that the Americans preferred. The difference in penetration between the 90 mm T15E2 and 105 mm T5E1 was minimal, but the T32 significantly surpassed its sibling in protection and was 10 tons lighter, as well as significantly shorter.


1 comment:

  1. Always love reading about prototype design processes. Thanks for the translaton

    ReplyDelete