Friday 27 October 2017

Heavyweight Brainstorming

During the years of WWII, American industry made excellent light and medium tanks. SPGs built on their chassis were no less excellent. The only field where American engineers encountered misfortune was the development of heavy tanks. Although the Heavy Tank M6 was built, and even entered service, it was quickly left behind. The tank turned out to be too heavy and insufficiently mobile, without a place in American tank doctrine. Nevertheless, work on American heavy tanks never stopped, and projects like the Chrysler K kept coming.

Superheavy tank, American style

Aside from the Ordnance Department and its composite offices, responsible for tank development, armoured vehicles were designed by private companies in the US. The most successful was Marmon-Herrington, the only company who managed to put several of its tanks into mass production. Mostly, these companies worked on light and medium tanks, but, according to correspondence with the Red Army GABTU, at least one company tried its luck with heavies. Of course, its chances of success were negligible, but such a risk often paid off in time of war.

On January 3rd, 1942, the People's Commissariat of Defense received a report from the manager of American department, Zarubin. It informed of negotiations in the fall of 1942 with Anatoliy Shelkin, a representative of the Leake Engineering Company, which, according to Shelkin, developed a large variety of heavy artillery tractors. An experimental prototype of one of these vehicles was shown to Amtorg representatives.

This was the vision of protection for prospective American heavy tanks in March of 1945.

What followed is much more interesting. During their next meeting, Shelkin claimed that Leake Engineering Company had designed a superheavy tank. According to the description, the vehicle weighed 175 tons. Sadly, no drawings were presented. The superheavy tank had 60-130 mm of armour, used "heavy and AA guns" for armament, and carried 6 heavy machineguns. Two steam engines with a combined output of 2500 hp powered this tank.

Shelkin said that the heavy tank would reach enormous speeds, and that the ground pressure would be no greater than that of one person's foot. The Leake Engineering Company used its tractors as a chassis. In case of interest, the company could provide materials on its 175 ton tank. However, negotiations did not move on past the proposal stage, even though information about this tank popped up in Soviet intelligence summaries several times.

By the summer of 1944, the American superheavy tank program was in a state of deep slumber. Its rapid awakening in the second half of July of 1944 was connected with the use of the Tiger II tank. On July 28th, the General Electric company proposed a draft project of the Heavy Tank M6A2E1. An urgent order to convert 15 Heavy Tanks M6A2 to the level of the M6A2E1 was cancelled, when it turned out that the overloaded chassis could not cross even slight slopes.

155 mm T7 gun, proposed for installation in the superheavy tank.

On August 14th, development of the T29 and T30 heavy tanks was approved, armed with 105 and 155 mm guns. meanwhile, starting in late 1944, German prisoners of war revealed that Germany was working on superheavy tanks. Most often, they spoke of the Maus, and even mentioned the place where it was being built: Boblingen. This was the truth, and the often mentioned Doctor Porsche had a direct connection with the development. It's hard to be surprised that the US began to work on its own superheavy tank design.

In March of 1945, Lieutenant Colonel Frederick Sumner Brackett from the Armoured Research Medical Laboratory, Fort Knox, Kentucky, conducted a study of prospective developments in armoured vehicles. One can assume that Brackett, a physicist and spectroscopist by trade, based his work on reports and summaries of American armoured vehicle development.

Brackett's result was a report, which was included in the overall report by the Council of Officers on the issues of equipping the US army in the post-war period. The report is dated June 20th, 1945. According to Brackett, the American army needed a 75 short (68 metric) ton tank, with up to 267 mm of armour in the front, and 102 mm thick sides. The 5-man tank would be equipped with a 90 mm gun, capable of penetrating 254 mm of armour from 1829 meters away at 60 degrees.

A 150 short ton (136 metric ton) semi-trailer tank concept.

One of the chapters of this document is intriguingly titled "Super-tank". According to the study, this role would be filled with a tank no less than 150 short (136 metric) tons in weight, with a 105 mm cannon in a fully rotating turret, an automatic loader, and a stabilizer. The thickness of its armour was stated as "highest possible". To make the tank easier to transport, it could be taken apart.

A sketch of a semi-trailer tank was attached, made by Sgt. Covington in March of 1945. The draft development of Brackett's superheavy tank was bold, to say the least. The tank was composed of two sections, each of which had its own engine. The front section contained the fighting compartment, manned by the driver and his assistant. The rear section contained the turret, similar to the one used on the T29/T30/T32/T34 series of tanks. The superheavy tank used a 155 mm gun. Aside from the main turret, a smaller turret with two machineguns was placed above the hitch.

Of course, there was no possibility of a more or less thought out technical project. However, this time the initiative came from the military, and a highly reputable agency at that. In addition, the development of superheavy tanks was included in the military's prospective projects program.

Prospective with a K

The defeat of Germany had a serious effect on the American tank program. Work on the T29 and T30 slowed considerably, as did work on the T28 SPG, which was officially called a superheavy tank at the time. Nevertheless, work continued, and a new argument for their acceleration soon came up.

On September 7th, 1945, at the Victory Parade in Berlin, new Soviet IS-3 heavy tanks were revealed. An especially unpleasant surprise was the fact that not just a handful of vehicles were on display, but 52 tanks. By September of 1945, 250 of them were coming out of Chelyabinsk every month.

A column of Soviet heavy tanks on parade in Berlin, September 7th, 1945. For a decade, these tanks served as a benchmark for development of armoured vehicles in Western countries.

The new Soviet tank that was shown in Berlin triggered a state of, if not panic, then certainly serious worry in the West. The Cold War had not yet started, but yesterday's allies already had cause for conflict. It was not surprising that the issue of America's superheavy tanks resurfaced in November of 1945. This coincided with the appointment of a rather remarkable character as the head of the War Department Equipment Board. This man was General Joseph Warren Stilwell, also known as "Vinegar Joe". During the war, he commanded the forces in Burma. Stilwell earned his nickname due to constant arguments with his allies and a rather harsh treatment of his own troops. Vinegar Joe had significant combat experience, but the fronts on which he fought saw little use of armoured forces, and Japanese tanks were far from what Germany had to offer.

The commission, unofficially nicknamed the "Stilwell Council", worked on a number of topics. Armoured vehicles were among them. Initially, the list of prospective programs included a superheavy tank, but it became one of  Vinegar Joe's first victims. The list that the commission approved on January 16th, 1946, had no superheavy tanks. The requirements for these vehicles were withdrawn, since they had no future.

Tank destroyers were binned shortly after. This decision was made based on experience that showed that the best tank destroyer is another tank. Self propelled guns were reserved for indirect fire and AA roles. The role of tank destroyers would be filled with heavy tanks, which had thick armour and powerful armament.

Model of the Chrysler K heavy tank, May 1946.

The T29/T30 and its offspring became the highest priority in heavy tank development. Nevertheless, work continued on other, less promising topics. One of them was a project, presented for inspection on May 14th, 1946. The author of this project was Chrysler Corporation's tank department. The project, indexed Chrysler K, was partially based on requirements for heavy tanks that were developed in 1945-46.

Despite the mass of designs and real tanks ranging from 70 to 75 short (63.5-68 metric) tons, some specialists were of the opinion that it should be limited to 60 short (54.5 metric) tons. This was the limit that Chrysler's engineers set for themselves. It was not easy to keep the mass under this line, especially since requirements for armour kept rising. It's not surprising that Chrysler came up with an extraordinary solution.

The location of the fighting compartment is the first thing that one sees. It was located in the rear of the hull. This allowed the tank to be shorter, mere inches longer than the M26 Pershing. The driver's compartment vanished. The driver and the other three crewmen were located in the turret.

This was not the first instance of such a solution. The first tank to gain this ability was the Medium Tank T23. Thanks to its electrical transmission, it could be driven from inside the turret, or even from outside the tank, using a remote control. This system was later removed, but Chrysler's specialists did not consider the turret controls as backups. Presumably, practical experiments were performed, and they showed promising results. 

The 105 mm T5E1 tank gun was typical for American heavy tanks of the era.

Moving the fighting compartment to the turret allowed for better placement of the engine and transmission. As with the T23, the Chrysler K would use an electric transmission. Like the drive sprockets, it was positioned in the front of the hull. An unknown 1200 hp engine would put the tank into motion. The mobility of the tank was unknown, but at 20 hp/ton, it could be expected to be even more agile than the Pershing. Overall, the suspension design was similar to that used on the T29/T30, as was the number of road wheels, but the width of the track links increased from 711 to 762 mm. The location of the drive sprockets was different. There were also no return rollers. This kind of layout was more characteristic of late German designs.

The hull and turret were also uncharacteristic for the American school. Unlike other American tanks of the period, which had cast hulls, the Chrysler K's hull was welded. The front and sides of the hull were sloped. The densely packed layout allowed the armour to be increased. According to the design, the front armour was 178 mm thick, and the sides were 76 mm thick. Except the T28/T95, no American tank had so much front armour. The turret also received similar armour thickness, taking an uncharacteristic hemispherical shape.

Vsevolod Martinenko's reconstruction of the Chrysler K.

The Chrysler K's armament was typical for American tanks of the era. Three types of guns were considered: 105 mm, 120 mm, and 155 mm. Chrysler's engineers took the lightest variant, the 105 mm T5E1 gun, which was used on the M6A2E1, T29, and T28/T95 heavy tanks. In part, this was because the number of loaders dropped to one. The increased workload was partially mitigated by a concentric positioning of ammunition.

The auxiliary armament of the tank was much more interesting. The American military had an obsession with hull machineguns since the 1930s. Entire batteries of machineguns stuck out from the hulls of light and medium tanks. On the Chrysler K, this idea was taken to a whole new level. Two Browning M1919A4 machineguns were placed in the front of the hull, and turrets with .50 cal Browning M2HB machineguns were placed in the rear corners. A General Electric remote firing system was used to fire these guns, a variant adapted from the Boeing B-29 bomber. Considering that aiming the hull guns with tracers resulted in questionable effectiveness, the remote control turrets would not be any worse, at least.

Precursor of the technological revolution

Fate was unkind to the Chrysler K. The gradual cutbacks made to military programs after 1946 hit tanks as well. Suffice it to say that the 1200 Heavy Tanks T29 ordered in May of 1945 dwindled to 8 by 1947. In these conditions, Chrysler's project, which required serious investments into development of a whole slew of systems, including an electric transmission, was out of place.

In addition, after conducting trials, the Americans favoured the 120 mm T53 gun, which was too big for the Chrysler K. For this reason, work on the tank only made it to the model stage. Vinegar Joe didn't outlive the tank by long. General Stilwell died on October 12th, 1946.

Placing the whole crew into the turret was a fad among American engineers in the 1950s and 60s, but it was first worked through on the Chrysler K.

Despite its sad finale, the Chrysler K left a mark on the American tank building school. In 1948, the American military decided that the mass of a tank should be capped at 58-60 short (52.5-54.5 metric) tons. The limit kept dropping, and the idea of a mobile heavy tank remained a priority. Tanks, including heavy ones, with the whole crew located in the turret, began appearing in 1952. None of them made it past drafts and models, but the idea persisted. In July of 1967, the MBT-70 entered trials, which finally implemented the idea of a turret-borne crew.


  1. General Stilwell was not 'commander of forces in Burma' he was Chief of Staff to the Chinese Army and briefly commanded the 10th Army. But yes, a remarkable character, totally unsuited to his assignment, which required someone like Eisenhower. he should have been put in charge of 15th Army Group in Italy.

  2. Do you have any way to access that report by Frederick Brackett?