Saturday, 23 June 2018

VK 36.01: Half a Step from the Tiger

Henschel's tank program looked somewhat comical in late 1941 and early 1942. The company was working on three heavy tanks at the same time. The lifeline of one of them, the VK 30.01(H), was just about to end, but work was still going on in December of 1941. The second tank being developed was the VK 45.01(H). Another tank, indexed VK 36.01, took the place between them in mass. The story of the first tank with a tapered bore gun that nearly went into production was far from simple.
Rapid weight loss

The VK 36.01 project appeared due to the "siege tank" program, approved by the Commander of the Land Forces, Major General Walther von Brauchitsch on November 24th, 1938. According to this concept, three tanks would be developed with the size and layout of the PzI, PzII, and PzIV. In the first case, the result was the PzI Ausf. F, in the second the PzII Ausf. J, and in the third, the VK 65.01. Initially, the VK 65.01 was indexed S.W. The 65 ton class tank would have 80 mm of armour. 75 mm and 105 mm guns (the latter would have a length of 20 calibers) were considered as weapons. A decision to install a 75 mm KwK L/24, the same gun as on the PzIV, was made in June of 1939.

The 25 caliber howitzer that was to be used as the A.W.'s main gun.

A project for another even heavier tank appeared around the time that the VK 65.01's armament was limited to that of the PzIV. Little is known about it, but its size was clearly larger than the VK 65.01. The mass of the vehicle named A.W. (Artilleriewagen, artillery vehicle) would surpass 80 tons, and its armour would be 100 mm thick. The Henschel company would develop the A.W., with the contract for the turret going to Krupp.

A 105 mm main gun would be used. Initially, the designers picked between a 20 caliber howitzer and the 10.5 cm leFH 18 with a barrel length of 28 calibers. On October 20th, 1939, Krupp presented another option. The 105 mm 25 caliber howitzer was taken as the starting point. The turret that housed this gun would need a 1750 mm wide turret ring, and its full width would be 2270 mm. The mass of the turret was also impressive: 8.4 tons.

The reworked A.W. would receive a weapon with the ballistics of the 105 mm leFH 18 howitzer.

The lifespan of this project was even shorter than that of the VK 65.01. Battles in France showed that the development of tanks that weighed more than 30 tons was pointless, since they would not be supported by existing river crossing equipment. The A.W. was the first victim of this new tank doctrine, adopted in early July of 1940.

However, the idea of arming a tank with a 105 mm howitzer remained. This weapon would allow tanks to combat more impressive fortifications than the 7.5 cm KwK L/24 could handle. Because of this, the A.W. did not die completely. On July 5th, Krupp received an order from the 6th Department of the Armament Directorate to develop a howitzer version of the VK 30.01.

The first variant was to receive a turret similar to the A.W.'s turret. The gun was replaced with an adapted 10.5 cm leFH 105. The front armour was thinned down to 80 mm, and the sides to 50 mm. The turret ring diameter was reduced to 1700 mm. In case the weight limit was still not met, the turret could be redesigned. Instead of typical Krupp style angled surfaces, the sides and rear of the turret would be rounded. Later, this layout would be used on the first variant of the VK 30.01(P), and then evolve into the Tiger's turret.

The second variant was for a howitzer version of the VK 30.01(H) turret. During the design process  that started in the fall of 1940, this was the preferred variant. The reworked turret would also have 80 mm of armour in the front and 50 mm in the sides. The final choice of the converted turret (called D.W. Turm in correspondence) was made in January of 1941. The turret received a cast gun mantlet. Prior to this, Krupp strived to avoid casting when designing tank turrets.

The stamp on one of the first VK 36.01 blueprints, March 1941.

In parallel with work on the turret, Henschel was redesigning the chassis. The front armour became 80 mm thick, and the floor was thickened to 25 mm. It was clear that a tank with these characteristics could not remain in this weight class, and the limit was lifted. The reworked chassis was named VK 36.01.

The increased strain forced a serious redesign of the chassis. Little remained from the VK 30.01(H). Even the hull, especially the rear, was changed. Amusingly, Heinrich Kniepkamp, who had a lot of influence on the development of the VK 36.01(H), kept trying to shoehorn elements from lighter vehicles into it. The chassis repeated the same metamorphosis as was seen on the VK 6.01 (later PzI Ausf. C) and then migrated to the PzI Ausf. F and PzII Ausf. J. Even the design of the evacuation hatches in the sides was borrowed from the light tanks. The same happened with the running gear. The 700 mm road wheels were discarded, and instead 800 mm road wheels were used. The number increased to 8 pairs per side. At the same time, return rollers were eliminated. The track links remained the same width as on the VK 30.01(H), but their pitch was reduced to 130 mm, and a second tooth was introduced on each track link.

A decision was made to increase the mobility of the new heavy tank. The 17.4 L V-12 450 hp Maybach HL 174 would be used. The transmission consisted of the 8-speed semiautomatic Maybach Olvar 40 12 16 and Henschel L 600 C turning mechanism. The tank's top speed was estimated at 50 kph, and the transmission was designed to suit it.

Heavy tank destroyer

Work on the chassis and turret of the VK 36.01 entered the active phase in the spring of 1941. At the time, Krupp and Henschel moved from working on the general concept to drawing blueprints. Krupp received an order for 4 hulls on March 6th. Two were due in January of 1942, and two in February. On May 5th, Krupp signed contract SS-006–4086/40 for four turrets. By then, Germany was working on four types of heavy tanks. In addition to the VK 30.01(H) and VK 36.01, Porsche was working on the VK 30.01(P) with more powerful armament. Work on the successor of the VK 65.01 also restarted by the spring of 1941. It is likely that this work formed the basis for the Soviet intelligence report on new German heavy tanks. The VK 36.01 matches the description of the "Type V", the VK 30.01 (P) is similar to the "Type VI", and the prospective VK 70.01 was the "Type VII". This information triggered work on the "big three": the KV-3, KV-4, and KV-5. The KV-3 was envisioned as a temporary measure, and either the KV-4 or KV-5 would enter production in 1942. Until the end of 1941, the Soviet Union was ahead of Germany in heavy tank design.

One of the first sketches of the VK 36.01 equipped with the Waffe 0725 gun. The drawing is from a British report from 1947.

The Germans likely did not know about the Soviet pre-war heavy tank design program. However, rumours definitely made their way to Berlin. One can assume that they triggered the change in requirements that Hitler approved at a meeting on May 26th, 1941. The thickness of the front armour was increased to 100 mm, and the sides to 60 mm. In addition, guns with anti-tank capability joined short barrelled weapons, with the former given priority. 

The VK 30.01(P) was already designated to carry a gun with the ballistics of the 8.8 cm Flak 18, so penetration had to be increased further. However, this type of gun did not fit into the turret of the VK 36.01. The solution was the use of the Waffe 0725 with a tapered bore. The caliber at the breech was 75 mm, but 55 mm at the muzzle, which radically increased the muzzle velocity of the round. However, there was one caveat. Each shot from the Waffe 0725 cost one kilogram of tungsten. Germany had a very limited supply of this metal. Nevertheless, this gun was chosen as the VK 36.01's main armament.

Development of the 5th and 6th German heavy tank began on June 26th, 1941. The first was a response to the requirement to install a turret capable of carrying the 88 mm gun onto the VK 36.01 chassis. The second was an alteration of the VK 30.01(P) design.

The turret of the VK 36.01 was similar to the VK 30.01(H). Since a larger gun would be installed, the commander and his cupola were shifted to the left.

On June 11th, 1941, the 6th Department told Krupp that they will have to change their turret once more. The overall configuration of the VK 30.01(H) was preserved. However, the size of the Waffe 0725 was such that the commander could no longer sit behind it. His station and his cupola were shirted to the left. The gunner and loader's hatches were also changed.

The gun mantlet was also changed. Its thickness, as the thickness of the turret front, remained at 80 mm. The thickness of the sides was increased to 60 mm as required. The Waffe 0725 had a coaxial MG 34 machinegun with the TZF 9b binocular sight. The thickness of the front armour was increased to 80 mm. The rear was 60 mm thick. The approximate mass was now 40 tons, but the top speed was still estimated to be 50 kph.

Odd one out

The mass production of the VK 36.01 was already under question in July of 1941. One of the issues with it was supplying the Waffe 0725 with ammunition. Hitler hardly yearned for a weapon that would consume all of Germany's tungsten. For this reason, only 6 VK 36.01 tanks and 8 Waffe 0725 guns would be built. Later, the numbers of hulls ordered from Krupp went up to 8. In October of 1941 the tank received a new name. In correspondence, it was referred to as the Pz.Kpfw.VI Ausf. B (VK 36.01). However, this index was rarely used.

The only experimental VK 36.01 chassis. The VK 13.01 chassis is nearby.

The first hull of the VK 36.01 was completed in Essen in late 1941. Henschel was receiving more and more orders for other products. The company was one of the producers of the PzIII, Germany's main tank at the time. Heavy losses on the Eastern Front required increasing production. Because of this, the 6th Department ordered the reduction of the VK 36.01 batch to two vehicles. However, Krupp finished their job, having produced 8 hulls and 8 turrets. 2 Waffe 0725 guns were completed, but they were never installed in the turrets. Henschel also never finished the two chassis. According to documents, one chassis was finished in March of 1942, but the second was never finished, since the VK 45.01(H) had higher priority. This tank had a lot more potential, and its gun did not devour tungsten.

The Maybach HL 174 engine. This engine was used on the VK 36.01.

A decision was made to convert the 5 VK 36.01 hulls into the VKz 35.01 ARVs. The vehicles were to be equipped with the Seilwinde 22/40 winch, which could carry up to 40 tons of mass. The Maybach HL 174 was replaced with the more powerful Maybach HL 210, so the ARV had the same engine as the VK 45.01(H). They were meant to work in tandem. The idea of building the VKz 35.01 stemmed from the VK 45.01. There was nothing that the Germans could evacuate a knocked out or bogged down tank with. The Sd.Kfz.9, Germany's main tank recovery vehicle, could only handle tanks that weighed about 20 tons.

The contract for conversion of the five VK 36.01 hulls into the VKz 35.01 was given to FAMO, the company that built the Sd.Kfz.9. However, not a single vehicle was ever built.

VK 36.01 chassis on trials.

Another unfinished idea for the project was the replacement of armament. The 8.8 cm KwK 36 L/56 and the 7.5 cm KwK 42 (one of the names for the Waffe 0725) were not the only guns that were designed in the first half of 1941. Rheinmetall-Borsig began working on another 75 mm gun on Hitler's orders. The first prototype had a barrel length of 60 calibers and could penetrate a 100 mm plate at 60 degrees from 1400 meters. In February of 1942, a 70 caliber version with even higher penetration was developed.

At the same time, Rheinmetall-Borsig designed a turret was that similar to the one that Krupp designed for the VK 36.01. This turret was meant to be installed into the VK 45.01(H). The idea to install this turret on the VK 36.01 (the letter used another index, VK 35.01) appeared in June of 1942. This vehicle would be called VK 35.02. However, this project did not live for long, only to mid-July of 1942. The idea of using the 75 mm gun in the VK 45.01 was rejected, and Rheinmetall-Borsig was about half a year too late to save the VK 36.01.

Albert Speer (driver's station) and Ferdinand Porsche (wearing a cap) during trials of the VK 36.01, November 1942.

However, the VK 36.01 was not a waste of time. The vehicle was actively used by Maybach during the development of the VK 45.01 transmission. Both tanks used the same gearbox.

In addition, the VK 36.01 took part in various trials as a part of the development of Tiger tanks. The most famous one is the trials that were held on November 8-14th, 1942, in Bad Berka. Here, the vehicle was driven by Albert Speer himself several times. The VK 36.01 was tested not only without a turret, but without a dummy weight. As a result, the tank was not only lighter than its heavy cousins, but the DB and MAN VK 30.02 tanks. The VK 36.01 turned out to be the fastest. This lead was lost during off-road trials, where it lost to the VK 45.01 and the VK 30.02. In addition, the tank broke down. The trials decided nothing, since the VK 36.01's fate was already sealed.

VK 36.01 turrets remained at Krupp's warehouse.

The last events the VK 36.01 took part in took place in 1944. 8 turrets remained in Krupp's possession in various stages of completion. The idea to convert them info fortifications came up back in November of 1942. The turrets would finally receive their armament and use ammunition from the 7.5 cm Pak 41. The hydraulic traverse mechanism, gunner's seat, and loader's seat were removed.

However, there was an issue. Some equipment was destroyed in March of 1943 during the bombing of Krupp factories by the British. This bombing buried the project. Damage after the July 25th, 1943, raid was so heavy that the turrets were abandoned. The idea returned in May of 1944. Krupp received orders to convert 6 turrets, but did not even begin to carry them out until the end of the war. In the spring of 1945, the turrets were captured by the Allies.

4 comments:

  1. What ever happened to the left over hulls in the unsuccessful heavy tank trials. It would be thought that if anything else by removing their turret and perhaps even remove most of their armor they could be the armored recovery vehicles that Tigers and Panthers never seemed to find when they were needed.

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    Replies
    1. I remember at least one KV hull (probably more) being converted for that purpose, since they were close enough to being suitable.

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    2. There are requests, documented in unit reports, for T34s or M4s for use as recovery tractors.

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    3. Not really sure how you'd go about removing "most of their armour" given that's a load-bearing structural element... The turret-platform superstructure would be easy enough to simply cut off but that seems to be about the end of it.

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