Monday 12 April 2021

American Electro-tank

The use of multiple engines, suspensions, and transmissions on one type of tank was a unique feature of American tank building. The same thing happened with the prospective replacement of the Medium Tank M4. Development of three types of transmission and several types of suspension theoretically allowed the military to choose the most reliable variant that would then enter production. The result was unexpected. The Medium Tank T23 was chosen as a result of trials, but it never replaced the M4, although some of its elements came in handy.

Planned alternative

Work on the tank that would replace the Medium Tank M4 began in the spring of 1942. The Medium Tank T20 project was approved by the Ordnance Department and Ordnance Committee by the end of May. The full sized model was approved around then. The tank remained in the same weight category as the M4, but the firepower, armour, and mobility were improved. The transmission was moved to the rear of the hull and the gearbox, differential, and engine were combined into one unit, which made removal and installation easier. The tank used a reworked Ford GAA engine, a planetary gearbox, and a torque converter.

The second Medium Tank T23 prototype. Initially both prototypes were the same, but some changes were made to the second tank as a result of trials of the first.

The Medium Tank T20 did not retain this shape for long. There were several ideas about improving the tank's firepower. In addition to two 76 mm guns the idea of a 75 mm gun with an autoloader came up. The Ordnance Committee approved the development of three variants of the tank on August 26th, 1942: the T20 with the 76 mm M1 gun, T20E1 with the 75 mm M3 gun and an autoloader, and the T20E2 with the 3" M7 gun.

Later, on October 2nd, 1942, a fourth variant appeared: the Medium Tank T20E3 with the 76 mm M1 gun and a torsion bar suspension. This was just the beginning for the rapidly multiplying prototypes. On September 3rd, 1942, the Ordnance Committee recommended development of yet another variant: the Medium Tank T22. This tank had a mechanical gearbox. In practice there were many more differences since the project was given to a different contractor. As with the Medium Tank T20, the tank split into three variants with different armament.

Unlike the T20 and T22, the tank with an electromechanical transmission had the VVSS suspension.

This was not the end to the variants. The idea of further expanding the family of tanks came in mid-September of 1942. This time, instead of a planetary or mechanical gearbox, an electric transmission would be used. This idea came from the Heavy Tank T1E1 that was being developed by General Electric. A prototype of this tank was being tested at the Aberdeen Proving Grounds at the time, and Gladeon Barnes, Chief of Research and Engineering at the Ordnance Department, had a chance to drive it personally. As a result of these trials, the Heavy Tank T1E1 was going to become the main tank in the Heavy Tank T1 family. The advantage of this vehicle was that it was very easy to steer, although the electromechanical transmission was bulky and heavy. It seemed reasonable to create a medium tank with an analogous transmission, especially since T1 tanks with other gearboxes showed reliability issues during trials.

The rear of the hull differed from that of the tanks with the mechanical or planetary transmissions.

The variant with an electromechanical transmission received the index Medium Tank T23. Like the T20 and T22, the plan was to build three variants with different armament: the Medium Tanks T23, T23E1, and T23E2 respectively. However, the variants with the 3" M7 and 75 mm M3 were quickly discarded. A decision was made to build two Medium Tank T23 pilots with 76 mm M1 guns. As with the Heavy Tank T1E1, the contract was given to General Electric. Don't be surprised by this: General Electric was a multi-industry conglomerate that also built rail cars at its factory in Erie, Pennsylvania. Since the factory also built locomotives, it was quite capable of transitioning to military goods. Experience with the Heavy Tank T1E1 demonstrated this perfectly.

The second prototype had the same turret as other tanks from the T20 program, same as the first prototype had initially.

The future Medium Tank T23 was more than just a T20 with an electromechanical transmission. The suspension was revised for an unknown reason. Instead of a HVSS suspension, the T23 used the same VVSS suspension as the Medium Tank M4. The layout of the hull was also more similar to the T22 than the T20, specifically the fenders, toolboxes, and various small elements like tow hooks. This was a normal situation when orders were given to multiple factories. Even the fact that development was overseen by the Tank-automotive Center in Detroit didn't change much. There was a certain rationalization of components and nothing more. The only thing that the tanks had in common was the turret, and even then the T23 only had it in its initial state.

The engine deck was also revised.

The internals of the Medium Tank T23 were also very different. The Ford GAN engine worked with a T563A1 generator, which made for a smaller power pack than on the T20 or T22 (although this compactness was misleading). The generator powered two 84 E745A2 electric motors. The massive motors required a change to the rear of the hull, so it's not hard to distinguish the T23's rear from its competitors'. Like on the T20 and T22, the driver's controls were duplicated, but instead of levers the driver and his assistant were given controllers. This made the tank much easier to drive. A third reserve controller was stored in one of the toolboxes and could be installed in an emergency. The third controller could be used to steer the tank from the turret. A system of levers allowed switching between controllers. Auxiliary controls could be used for driver training or if the primary controller was disabled. Simplicity of driving and the ability to control the tank from multiple places were some of the T23's advantages, but there were drawbacks as well. The T23 weighed 32,885 kg, three tons more than the T20 and almost 1.5 tons more than the T22.

High priority

The situation with the T23 ended up being comical. One would expect the first tank to be ordered to also be the first tank built, so the T20 would be expected first. The situation was the opposite: while the first T20 was delivered in May of 1943, the Medium Tank T23 prototype with registration number U.S.A. W-3098787 entered factory trials in January of 1943.

The driver's compartment. Thanks to the electromechanical transmission, it was very different from the T20 and T22.

The electromechanical transmission was a novelty, and so the first Medium Tank T23 was essentially a test lab for General Electric. The prototype drove for 3680 km at expedited trials held at Erie, a distance that its competitors could only dream of. The top speed was the same as on the Medium Tank T20: 56 kph. Complications with temperatures in the engine compartment, one of the biggest issues of the T20 and T22, were not mentioned. Even the first prototype of the Medium Tank T23 showed itself to be superior to its competitors. As mentioned above, trials began far in advance of the others, and time was of the essence.

Close up view of the driver's compartment hatches.

Like many other prototypes, the Medium Tank T23 changed during these trials. The biggest change was the turret. There is no precise information on whether the change was made during initial assembly or later, during trials. Either way, all photographs of the tank show a completely different "head". Work on this turret started earlier, in the summer of 1942, during work on installing the 76 mm Gun M1 in the Medium Tank M4A1. The stock turret was too small. The gun could fit, but it was uncomfortable to work with. It was also unbalanced and required an 800 kg counterweight. All this happened after the T20's turret was already finalized. There is reason to believe that similar issues were discovered during gunnery trials of tanks from the T20 family.

Partially opened engine deck hatches.

A solution was quickly found. First, the M1 gun was shortened by 381 mm. This had nearly no effect on its characteristics, but the balance improved significantly. After trials, this gun was accepted into service as the 76 mm Gun M1A1. This gun in the Combination Gun Mount T79 was later installed in the second Medium Tank T23 prototype. The turret of this tank was the same as the one used on the T20 and T22.

The idea of a combined power pack was preserved. The engine was removed together with the generator.

The first prototype went further. Work on a new turret for the GMC M10 began in early 1943. This welded turret had the Combination Gun Mount T80 with the same 76 mm M1 gun. The only difference was that the gun mantlet covered the full width of the mount, improving protection. Later this turret was used on the Gun Motor Carriage T72. The design served as the foundation for the E6194 turret for the Medium Tank T20. Unlike the turret designed for the GMC T72, the tank turret had a roof, thicker armour, and a port for throwing out spent shell casings. The attached memo explained that the turret was designed to protect against 37-75 mm shells.

One of the few known photos of the first Medium Tank T23 prototype. It used a welded turret.

Two turrets of this type were made. The first turret was installed on the first Medium Tank T23 prototype, the second was shot up. The tests were done with shells more powerful than those its was intended to protect against: 76 mm M62 and 90 mm M82. The result was predictable, but the turret fared quite well. However, the idea was not developed further. First of all, the overall layout of the E6194 turret wasn't much different than the regular T20/T22/T23 turrets. Second, moving from cast to welded turrets would be quite painful from the manufacturing point of view. All that these trials and the whole welded turret project proved was that the new gun mount was much better than the T79.

One of the two welded turrets produced for trials on the T20.

It was already obvious that the welded turret was just a backup plan. A different cast turret was developed in parallel. A number of change requests were taken into consideration, including those that improved crew conditions. Like the E6194, the turret was given the T80 gun mount. It also had a large bustle. The hatches were noticeably changed. The commander's hatch moved to the left and was now used by the loader. The commander got a new hatch in a cupola that contained 6 periscopes. This design gave the commander good visibility without him having to poke his head out. A model of the turret was built in the spring of 1943, then a prototype. This turret was chosen for subsequent Medium Tanks T23.

The T80 gun mount offered better protection.

The early completion of the Medium Tank T23 project had an effect on the second prototype. It was finished in March of 1943 and had some differences. The hull was reworked, for instance the driver's compartment hatches were enlarged. The turrets were also different. As mentioned above, the second prototype had the same turret as the T20/T22. Instead of T51 tracks, the second prototype received T48 chevron tracks.

The turret was designed to withstand 37-75 mm shells, but was tested with 76 and 90 mm shells. The result was predictable.

Unlike the first prototype, the second was meant for military and proving grounds trials. The first prototype joined it later. Of course, the electromechanical transmission started showing growing pains once it left the ideal conditions of the factory. Increased wear of transmission elements such as generator brushes was noted in dusty conditions. Trials held at the Aberdeen Proving Grounds, Fort Knox, and Desert Training Center in California resulted in a list of required changes to the design of the tank. The list contained many demands to improve the reliability of the electromechanical transmission in extreme conditions.

An enlarged cast turret that was more comfortable for the crew was developed in parallel.

Despite these issues, General Electric's tank was in the lead. It had its problems, but it had the advantage of easy driving. Compared to the Medium Tanks T20 and T22 the electromechanical transmission performed rather well. The T23 wasn't prone to engine failure or overheating. It's not surprising that the Ordnance Department and Ordnance Committee turned to the T23 as the best candidate for replacing the Medium Tank M4. On May 6th, 1943, the Ordnance Committee recommended building a batch of 250 tanks. The decision was approved a month later on June 3rd.

Too complicated!

The decision to mass produce the T23 didn't mean that the design would stop changing. Requirements for armour protection increased in the summer-fall of 1943. The upper front plate was thickened to 76 mm. Various changes developed as a result of trials of the two prototypes were also made. These changes meant that the design of the Medium Tank T23 was only finalized in the fall of 1943. Changes led to the mass increasing to 33,66 kg. This increase led to unpleasant consequences that were only discovered later.

One of the first production T23 tanks at the Aberdeen Proving Grounds.

The work on a cast turret with the T80 gun mount resulted in the D82081 turret. Unlike the welded turret, the D82081 was put into production immediately without a prototype. The final variant of the turret received a 2" bomb thrower in the front left corner of the roof. It was used by the loader. The improved variant of the T80 gun mount was standardized under the index M62. The gun mantlet was thickened to 89 mm. Hooks for carrying the AA machine gun were added to the rear of the turret bustle.

The chassis of the production vehicle didn't change much.

Unlike the turret, the chassis of the production Medium Tank T23 didn't change much. The assembly method changed slightly, particularly the upper front of the hull was now welded together from several cast and rolled parts. This wasn't surprising as the production T23 was built at the Detroit Tank Arsenal. The equipment also changed: spare track links were moved to the front of the hull, a travel clamp was added in the rear. There weren't too many changes to the chassis from the second prototype.

The biggest difference was the D82081 turret.

The plan was to build 250 tanks at the Detroit Tank Arsenal with registration numbers U.S.A. W-30103052-30103301. The contract was altered several times, but it ended up being largely the same. The difference was that the final contract included Medium Tanks T25 with serial numbers U.S.A. W-30103053 and U.S.A. W-30103054 that deserve their own article. As for the first production Medium Tank T23, it was ready on October 19th, 1943. The tank was sent to the Aberdeen Proving Grounds. 5 more production tanks were sent to Fort Knox.

The turret was superior to its predecessor. One significant improvement was the increase in vision.

The production Medium Tank T23 travelled for 7040 km during trials at the Aberdeen Proving Grounds. Soviet military representatives witnessed these trials. In a conversation with the Soviet delegation, American tankers mentioned that the T23 was going to be standardized. However, the Soviet delegation noticed one issue that could be cause for worry. The suspension remained the same as on the Medium Tank M4, despite an increase in mass and therefore ground pressure. The road wheel tires on the tank under trial were noticeably disintegrating. This was already the second set of road wheels, as the first one had long become unusable. 

One of the production tanks sent to Fort Knox for trials.

The trials of the five tanks sent to Fort Knox (later that number increased to 10) were much more eventful. The testers had the same problems with road wheels. It was clear that using the M4's suspension as it was a risky move. There were also issues with the Ford GAN carburetors and the electromechanical transmission. The military didn't spare its tanks and they were used in rough conditions. It turned out that the transmission needed protection from water. Changes had to hurriedly be made to pilot tanks and prototypes.

Army trials showed that the tank was vulnerable to dust and servicing the electromechanical transmission was too difficult.

The issues with the electrical system were just icing on the cake. The military ran into a whole spectrum of issues with using the tank. It's well known that tanks don't fight on their own. They need various support, for instance repair crews. Servicing the electromechanical transmission and other complex systems proved too difficult for them. The tank was simper to drive, but more difficult for everyone else. Compounded with the suspension issues, the T23's chances of seeing combat were dwindling.

The experimental Medium Tank T23E3 with a torsion bar suspension.

The critical situation with the tanks had little effect on the production plans. By June 1st, 1944, the Detroit Tank Arsenal delivered 57 Medium Tanks T23, and the factory was behind schedule at that. 35 tanks were due every month. One issue was delays in shipments of generators and electric motors from General Electric. However, the Ordnance Department understood perfectly well where things were headed by the end of the spring of 1944. T23 production continued by inertia, especially as development of the T25 and T26 were behind schedule. These tanks had more powerful armour and armament. Production of the Medium Tank T23 ended in 1944.

The tank turned up when the Medium Tank T23 program was already written off.

By the summer of 1944 the Ordnance Department didn't even try to hide the fact that the T23 was essentially being produced as a test bed for various design elements. The tank was transitional and not suitable for combat. There was reason in this, as even without all of the technical issues the Medium Tank T23 was nearing obsolescence in July of 1944. The tank was adequate for training and testing solutions for more viable vehicles. The Americans got an equivalent of the Covenanter, although not built in such large numbers.

The turret also changed in addition to the chassis.

One offshoot of the Medium Tank T23 program was the Medium Tank T23E3. The Ordnance Committee recommended its development on April 15th, 1942. The work was approved on May 6th. In practice, the work on the T23 with a torsion bar suspension was delayed. The slow progress of T23 production and poor showing of the Medium Tank T20E3 in trials had an effect. The torsion bar suspension turned out to be heavier and less reliable, not suitable for production in its current form. Meanwhile, the Ordnance Department met the suspension with great enthusiasm and even suggested standardizing the Medium Tank T23E3 as the Medium Tank M27. However, the idea was discarded after the results of T20E3 trials (planned for standardization as the Medium Tank M27B1).

The tank was different on the inside. The ammunition capacity could be increased as a result of removing the turntable.

Work on the Medium Tank T23E3 started only in December of 1943. A tank with serial number 19 and registration number U.S.A. 30103068 was taken. The tank already needed work, as it was built before trials at Fort Knox revealed a ton of issues with the electric transmission. Both the transmission and suspension had to be replaced. The fighting compartment turntable was also removed, which allowed the designers to increase the ammunition capacity to 84 rounds for the 76 mm M1A1 gun. The order was reduced from two pilot tanks to one in May of 1944.

Driver's compartment on the Medium Tank T23E3.

The main objective was to replace the suspension. Like the T20E3, the T23E3 got a torsion bar suspension with six wheels per side. Shock absorbers were installed on the first, second, fifth, and sixth wheels. The suspension was reinforced after the poor showing on the T20E3. The road wheels were redone and the Sheldrick metallic track links were widened to 483 mm. The mass of the tank increased to 35,834 kg.

A Medium Tank T23 converted to take the HVSS suspension.

The modernized Medium Tank T23 had a poor fate. The tank was converted in July of 1944, when further work on the subject was already stopped. The only reason why the T23E3 was still built was that the mass and suspension were the same as on the Medium Tank T25E1. After a 100 mile run that revealed minor suspension defects, the tank was first sent to Aberdeen, then to Fort Knox.

Modernized tanks were also given T80 tracks.

An effort was made to improve the suspension of production T23 tanks. It was clear that the suspension was too weak for the mass, and so a tank with a new suspension was recommended: the T23E4. It would have have an HVSS suspension, but this work was never approved. Nevertheless, three production tanks were modernized in 1944. The HVSS suspension with T80 tracks was installed.

Trials showed that the modernization had an effect. The tank ran much better off-road.

Three modernized tanks with serial numbers 624, 625, and 626 arrived at Fort Knox in December of 1944. Tank 624 was chosen for mobility trials. It had already driven for 1107 km. Even though the mass grew to 37,195 kg, trials in difficult conditions showed that the idea was correct. The trials report showed that the tanks with a HVSS suspension worked much better than ordinary T23s. The modernized tank also made for a better gun platform. The problem was that by the start of 1945 it was obvious that the torsion bar suspension was the future. This suspension redeemed itself and became the priority in the summer of 1944, while the HVSS was relegated to the Medium Tank M4 family.

The fate of the Medium Tank T23 was a poor one. Like the Heavy Tank M6, these tanks never saw battle.

The military's opinion of the Medium Tank T23 can be gleamed from the fact that the idea of sending these tanks to Europe received no support even during the crisis in the Ardennes. In a way, these tanks were already fighting since June of 1944. The man responsible for giving the Sherman a 1750 mm wide turret ring deserves the Medal of Honor, as the large turret ring migrated to the T20/T22/T23 family. The idea of installing the D82081 turret on the Medium Tank M4 was voiced in December of 1943. Pressed Steel delivered its first 100 Medium Tanks M4A1(76)W in January of 1944. By June of 1944 the American army already had hundreds of medium tanks with 76 mm guns and new turrets. The approaching obsolescence of the Medium Tank M4 was pushed back and the need for another tank with the same turret and gun but a new more complicated transmission seemed poor. Meanwhile, work on replacing the Medium Tank M4 continued.

1 comment:

  1. "The testers had the same problems with road wheels. It was clear that using the M4's suspension as it was a risky move."

    Think a second 'was' is missing from that sentence as it caused me to take a second to reread it, but fantastic article nonetheless. If you get the chance to, Ft. Benning has one of the T23's in their National Armor and Cavalry Collection for viewing when they do Open House days.