Armoured Confusion: Victorious '45

There are many misconceptions about the use of tanks in 1945, same as any other period of the Great Patriotic War. These myths muddle the characteristics of tanks, their application, and sometimes even introduce tanks that were not there at all. The final chapter in the series dedicated to myths on Soviet armour in the Great Patriotic War is dedicated to this period.

Wrong Place, Wrong Time

 Work on Soviet heavy tanks split into two directions in 1944. One was the development of a new heavy tank, called Object 701. The second was the improvement of the IS-2 heavy tank, which later split into a minor and a major modernization projects. The former led to the creation of an IS-2 tank with a straightened upper front hull. Finally, a third tank came up in the spring of 1944 on factory #100's initiative. This tank was called IS-6 and turned out to be the odd man out.

IS-6 Drama

"To GBTU representative, Engineer-Lieutenant Colonel comrade Markin

Having taken the post of the GBTU TU representative at factory #100 in April of 1944, I already reported that my work at the factory is made difficult because of the fact that the factory is hiding experimental work from me, which has now resumed at the factory. At first, this secrecy was obtained by organizing a special room, which only comrade Kotin and a short list of other people were permitted to enter. I was not included in this list (at the time, the design of the IS-6 tank was being kept secret from me).

Wishlist Response

"To the Marshal of the Armoured Forces, comrade Fedorenko

The tactical-technical characteristics that you sent are viewed by us as a task to develop new prospective types of heavy tanks that are not yet put into practice in tank building.

As you do not have any objections regarding the requirements for the IS-6 that I approved and confirm that it is necessary to build such the IS-6 with a mechanical transmission, I consider that it is at the same possible to build a tank with an electrical transmission using the same requirements. 

Development of a tank with an electrical transmission will allow us to demonstrate the advantages and specifics of this transmission compared to a mechanical transmission and determine its potential in the creation of more powerful tanks.

We have the following notes about a number of tactical-technical requirements that you provided.

Launch of the IS-6

"Order of the People's Commissar of Tank Production of the USSR
Moscow

June 8th, 1944

Factory #100 (comrades Kotin, Yermolayev) jointly with TsNII-48 (comrades Zavyanov, Kapyrin) developed a draft project of the IS-6 heavy tank, which has significant advantages in terms of armour compared to the IS-2 mass produced tank.

In order to ensure timely production and trials of experimental prototypes of the new IS-6 tanks, I order that:

Soviet Heavy Tank Characteristics

The following table compares the prospective post-war heavy tanks of the USSR (the T-34 is included for completeness' sake, but they seem to have merged the T-34 and T-34-85 into one tank). The table was approved fairly quickly after the war, since the IS-3 and IS-7 already have its index, but the IS-7 still has characteristics of the Object 257 rather than a later model, and the IS-4 is still referred to as Object 701.

Object 257: The First IS-7

The IS-7 heavy tank is well known to armour enthusiasts. A combination of impressive armour, a powerful gun, and an engine that could propel the 70 ton tank at 60 kph made it the pinnacle of its class. At the same time, no less than 7 vehicles existed under the IS-7 index, and three of them were called "Object 260". The creation of this vehicle is shrouded in mystery, partially due to the conditions of secrecy created at the factory #100 design bureau. Thanks to recently discovered archive materials, we can now see how the IS-7 (back then, still Object 257) developed in its early stages.

IS-6 Hulls

Proposals of upgrades to the hull of the IS tank. The mass produced IS is in the middle. The prototype on the left resulted in the IS-6.

A closer view of the tank that eventually became the IS-6.

One of several IS-6 prototype hulls undergoing ballistics testing. This one is marked "model #15".

World of Tanks: Today in History: IS-6

On June 8th, 1944, on the orders of the People's Commissar of Heavy Production, factory #100 in Chelyabinsk and Uralmash received orders to develop blueprints and build prototypes of the IS-6 heavy tank.

This vehicle, the first in the history of domestic tank building, was built with an electromechanical transmission. The V-12U engine powered a generator, which powered electric motors, which were connected to the drive wheels through planetary final drives. The electromechanical transmission was supposed to make controlling the tank easier and increase its maneuverability.

However, trials showed that the transmission has not reached desired levels of reliability. Additionally, it required a large amount of copper, which was in deficit. An IS-6 prototype with a mechanical transmission showed that the IS-6 did not surpass the IS-2 or IS-3 in maneuverability, protection, or firepower. As a result, the tank was not adopted into mass production.

Original article available here.

Electrical Transmission

"May 2nd, 1944
Technical project of a heavy tank electrotransmission at factory #100

Main specifications:

1. Nominal engine power at 2100 RPM: 620 hp.
2. Power diverted to the fan: 70 hp.
3. Ventilation: the fans will be powered by electric motors, powered from a special generator.
4. The diesel engine is started using a battery through the generator.
5. The tank's mass is 50 tons.
6. The "star" diameter is 700 mm.
7. The conversion factor for the final drive is 13 with a coefficient of useful work of 0.92.
8. The maximum RPM of the motor is 4050 RPM.
9. The long term operation mode of the motor is at a ratio of pulling force to weight of 0.27.
10. The hour-long operation mode of the motor is at a ratio of pulling force to weight of 0.36.
11. The maximum operation mode of the motor is at a ratio of pulling force to weight of 0.9.
12. The maximum torque of one motor during a turn at a speed of 5 kph is 950 kg-meters.
13. Dimensions of the electric motor:
1. External diameter: 720-740 mm
2. Length (including connector) 650 mm
14. Dimensions of the generator:
1. Diameter: 930 mm
2. Length: 600 mm

Clarifications of technical details is underway, assuming a joint working-out of the project by July 1st of this year."

CAMD RF 38-11355-2211

Comrade Vovk and the Chamber of Secrets

Decades after the fact, documents on tank development are scattered throughout archives. You can't go into CAMD and open the IS-4 box to get everything and everything on the project. You'd think that it would be a lot easier to get information on the projects at the time of their creation, provided you had proper clearance. You'd be wrong.

"To the chief of the Red Army GBTU TU, Major-General of the Tank Forces, comrade Afonin

I send to you the report of the senior military representative at factory #100, Guards Engineer-Lieutenant-Colonel colonel Vovk. I think that the facts of the matter violate the proper behaviour towards military representatives, especially senior military representatives, and require immediate action.

Without a concrete plan of experimental works, factory #100 performs discretionary research, which brings little benefit to producing new tanks or improving already existing ones.

Through a private means, I discovered that factory #100, led by comrade Kotin, is developing a new vehicle that is a counter to Object 701. When requested details on this project, comrades Kotin and Soloduhin officially stated that no such work is being performed at the factory.

When comrade Vovk was appointed as the senior military representative at factory #100, he happened upon a "mysterious room", to which he was not admitted, which is described in the attached report. At the same time, most work on subjects such as approval of IS blueprints and technical documentation have not been completed: steel plate radiator, planetary transmission, improvements of the gearbox, AA mount, driver's seat, final drive gears, V-2IS engine defects, etc.

I ask you to act on the leadership of factory #100 and restore firm control of the factory by military inspectors, especially regarding hiding experimental work. The leadership must be reminded of the role of the military inspectors in accordance to a Government Decree well known to you.

GBTU KA representative, Engineer-Lieutenant-Colonel  Markin
April 22nd, 1944
Attachment: report on 1 page

To the GBTU KA representative, Engineer-Lieutenant-Colonel comrade Markin

After my appointment to the role of senior military representative at factory #100, I encountered the following situation:

When familiarizing myself with the work of the design bureau, I discovered a room, which was guarded by factory staff. They denied me entry, stating that only a note from General Kotin can grant access. When I met comrade Kotin, I told him of the event, to which he answered "This is my personal office". In reality, this room is occupied by Schneidman, Shashmurin, Turchaninov and Mitskevich, who replied to my inquiry of what goes on in that room with "it is a smoking room".

It is evident that the factory is conducting work which are being hidden from me. On April 12th, 1944, an AA mount for Goryunov's machine gun arrived. It should take 3-4 days to figure out how to mount it on the tank. No work has been done by this point, and my demands are being ignored. Factory director comrade Kotin gave it to the chief engineer, comrade Belyakov, and told him "if it doesn't take too long and will not compromise the quota set by the People's Commissar, then do it".

I checked, and the factory does not have a quota for either the second quarter or the month of April set by the People's Commissariat of Tank Manufacturing; the factory is working to quotas it set itself.

As a result, the Goryunov AA mount is not ready. I consider the above abnormal, and ask for directions on what to do.

Senior Military Representative of the Red Army GBTU at factory #100, Guards Engineer-Lieutenant-Colonel Vovk.
April 18th, 1944."
CAMD RF 38-11355-2214

The situation didn't improve one year later.

"To the Director of factory #100, Lieutenant-General of the Engineering-Tank Forces, comrade Kotin

The GBTU KA representative at the Kirov factory, Engineer-Lieutenant-Colonel comrade Markin and senior military representative at factory #100 comrade Vovk reported that the working conditions at factory #100 are such that he cannot fulfil his duties.

The impeding work conditions consist of employees hiding a portion of experimental work performed at the factory. This treatment of military inspections violate the Decree of the Committee of Defence of the USSR SNK from July 15th, 1939 #204, "On military representatives of the People's Commissariat of Defence in industry".

I ask you to take necessary measures to create proper working conditions for military inspections in accordance with the above Government Decree.

Deputy chief of the Red Army GBTU Lieutenant-General of the Engineering-Tank Forces Lebedev
Chief of the Red Army GBTU TU, Engineer-Lieutenant-Colonel Blagonravov

April 10th, 1945"
CAMD RF 38-11355-2805

Judging by the dates, the former secret project would have been the IS-6, and the latter one Object 260 (IS-7).

Penetration, Part 4

This article covers a number of guns from 1945. Some of them you have seen before, some of them are new.

CAMD RF 38-11369-696

The header row lists the guns the document covers: 85 mm D5-85-BM (factory #9), 85 mm D10-85, 85 mm S-34-IV (TsAKB), 122 mm S-34-II (TsAKB), 122 mm D-30 (factory #9), 122 mm BL-9 (OKB-172), 122 mm S-26-I (TsAKB), 130 mm S-26 (TsAKB), 152 mm BL-10 (OKB-172), and the 122 mm BL-13-1 (OKB-172). 

The second row shows the vehicle class the gun would have been mounted on. The first three 85 mm guns are for medium SPGs (presumably, it just says SU). The next two 122 mm guns are for the Object 701 (IS-4) and IS-6 respectively. The next 4 guns of various calibers are for heavy SPGs (same, but ISU). The last gun is marked for the IS-6, but crossed out. 

The next row is for the muzzle velocity of the shell, AP (top) and HE (bottom). The row after is for maximum ranges. The range of most guns in the ISU is limited by the gun's elevation, rather than the propellant.

After that is what we came here for, the penetration values. The numbers for the D-30 are similar to that of the D-25 we have seen in previous tables. The penetration of the BL-10 is a little lower than the value in the first article of this series; it has been reduced by 4 mm at 100 meters, and also drops off faster. 

The D5-85-BM, on the other hand, received a marginal improvement. The D10-85 blows it out of water with penetration surpassing that of the slower 122 mm guns. The S-34-IV performs similarly. 

The line after that is the rate of fire. After that, ammunition capacity. After that, crew members in the gun's vehicle. 

Improving the IS-2

The IS-2 model 1943 (at this point, still indexed IS-122) was a fearsome opponent for enemy tanks, infantry, and fortifications alike. However, there was still room for improvement. The following document outlines some proposed changes to the tank.

"Measures to increase the combat ability of the IS-122 tank

1. Turret and hull

1. A hull whose strength matches the armament may only be reached by replacing the clearly obsolete shape of the upper front plate. The front of the IS-122 must be shaped like the front of the T-34, with a 120 mm rolled armour plate (figure #11) within the limits of the tank's dimensions (figure #12).

Figure #11. Parallel cross-section of the front of the IS-122 tank hull. 

Figure #12. Front of the altered IS tank hull. 

The necessity of producing this type of front hull is confirmed by penetration tests of the front plates of the Panther tank with the German 88 mm gun from the Ferdinand SPG. The upper front plate of the Panther tank, 85 mm thick and sloped at 55 degrees, could be penetrated with armour piercing shells at 600 meters. The altered front of the IS-122 tank hull will be impenetrable by armour piecing shells from the 88 mm gun (Ferdinand SPG) at any distance.

The front of the turret should be 200 mm thick, turret sides 150 mm thick. 

2. Increase in fuel storage, ammunition capacity, and crew comfort may be reached by increasing the width of the hull within the dimensions of the tank (figure #13). 

Figure #13. Perpendicular cross-section of the IS-122 tank hull.

Due to obvious advantages of rolled armour over cast, the upper hull should be produced with rolled armour. By placing the sides at 45 degrees (instead of the current 15), the thickness of the plates could be reduced to 75 mm.

2. Armament

1. Due to the outlines disadvantages of the 122 mm gun (two-piece ammunition, screw breech), it is necessary to replace it with a smaller caliber gun of equivalent power (preferably 100 mm). "

- CAMD RF 38-11355-2369

A lot of these features were implemented in the model 1944 modernization, but not all. For example, the 100 mm gun projects never really got anywhere. Instead, the gun was equipped with a superior semi-automatic sliding breech, but kept the two-part ammunition.  

One-part ammunition was definitely attempted.

CAMD RF 81-12038-697

"To the Chief of the GAU KA, Marshall of Artillery, comrade Yakovlev

Regarding the letter from GAU KA from May 12th, 1945 on the topic of order 940670ss, I report that as a result of GOKO decision #6863ss on November 4th, 1944, NKV factory #9 developed an experimental 122 mm D-25 gun that uses one-piece munitions, and sent it to the Kirov factory on May 21st, 1945, in order to be mounted in the IS tank

D. Ustinov"

I don't envy whoever had to serve as the loader on that experimental tank. 122 mm ammunition is rather large.

T-44, first variant, with 122 mm gun, demonstrating the dimensions of the shell.

Here are models of the existing IS-122 (center) and proposed hulls, surrounding it. Neither was used, but the right one inspired the IS-6 hull shape.

As for the ammunition storage on the IS, here is an attempt to increase it.

CAMD RF 38-11355-2606

The diagram is a bit convoluted, but it makes a lot more sense with the labels:

"Diagram #2. Placement of 122 mm ammunition in the IS-122 tank.

1. Thirteen armour piercing tracer shells in the turret bay.
2. Fifteen high explosive fragmentation grenades in the turret bay.
3. Three additional shells affixed with belts to the lids on the ammunition crates.
4. Twenty six propellant casings in the fighting compartment, and two on the side of the turret.
5. An additional placement of three casings with propellant placed as follows: one on the lid of the left ammunition crate, one in the front left corner of the hull, one in the right hull bay."

D-30 Gun for the IS-6

In 1944-1945, Soviet heavy tank industry was at its peak. A very interesting vehicle was being developed, the IS-6. Unlike its "predecessors" IS-3 and IS-4, (IS series indexing was not at all sequential), it did not just get a D-25T, but a more advanced gun, the D-30:

CAMD RF 81-12038-681

"On the question of experimental works at factory #9 for the 4th quarter

In addition to the experimental works at factory #9 that I have wrote about in quarterly reports, the following were completed in the 4th quarter:

1. 122 mm "D-30" tank gun with ballistics from the "D-25" tank gun.

Factory #9 completed experiments on the prototype tank gun (under its own initiative), which consists of:

1. D-25's monobloc;
2. D-10's breech and gas block;
3. Balancing mechanism with two springs;
4. Lengthened D-25 mount;
5. Fume extractor mechanism.

The experimental D-30 system was tested by firing 30 special strengthened shells from a special stand.

Before shooting, markings were placed on the D-30. The gun fired 30 shells successfully. After shooting, the markings were not deformed. All mechanisms of the gun perform satisfactorily. The full report on the D-30 test was sent to the GAU Artkom indexed #1595/42s on December 5th, 1944 by factory #9. 

In December, after the tests, the gun was sent to factory #100 for installation in the IS-6 tank and continuation of trials."

The D-25 was considered powerful enough for years to come, and, as such, its firepower was not increased. However, the rate of fire was increased in two ways. One is the improved breech, which makes loading easier. That's not that interesting, at least not as interesting as the fume extractor. Existing IS-2 tanks could already fire fast enough that ventilation of the crew compartment could not keep up. The fume extractor expelled the fumes from the burning gunpowder from the front of the barrel, so they could not rush back when the breech was open after a shot, allowing the tankers to fire much faster without succumbing to CO poisoning. 

Birth of the IS Tanks Part 3: IS-100 and Beyond

Even after the vastly successful D-25T gun was chosen for the IS, experiments with the armament of the IS continued. Immediately after the failure of the 107 mm ZiS-6, Grabin's construction bureau hedged their bets on a 100 mm gun based on the naval B-34, similar to the S-3 field gun already being developed. The resulting tank gun was indexed S-34. It also had a mechanism to ease loading and increase the rate of fire. The D-5T-85BM, a higher power 85 mm gun, was also in the running, as well as another 100 mm gun, D-10T. Since the IS-85 and IS-122 were renamed to IS-1 and IS-2 by this point, these new prototypes were named IS-3* (Object 244, with a D-5T-85BM), IS-4* (Object 245, with a D-10T) and IS-5 (Object 248, with an S-34). The IS-3* was rejected due to insufficient muzzle velocity, and thus penetration, of its gun. Initially, out of the remaining designs, the IS-5 was going to win the title of IS-100 and begin production, but both ended up being built. The IS-4* and IS-5 can be distinguished by the position of the commander's cupola: the IS-5's gun required a gunner to the right of the gun, flipping the internals of the turret. The turret also would contain a loading mechanism and a gun stabilizer, but they were not present in initial trials. IS-5 was deemed superior, due to better ergonomics of the loader and gunner, but both designs had some problems that had to be resolved. The D-10T gun was more reliable, but made the loader's job more difficult, and only allowed to carry 30 shells. The S-34 threatened to smack the commander when it recoiled. It was recommended to move him even further right. In October of 1944, the IS-5 turret was finalized. With its loading mechanism and stabilizer, it was superior to every existing heavy tank in terms of rate of fire and accuracy on the move. However, in Malyshev's letter to Beria on October 18, 1944, he wrote: "...[122 mm guns] can now fight any German tank at a distance of 1700 meters and greater..."

The following points supporting the IS-100 were outlined in the letters between Malyshev, Beria, and Fedorenko:

• Increased rate of fire (up to 8 rounds per minute)
• Increased ammunition capacity
• Lack of muzzle brake improves working conditions for the gunner
• The tank is 500-600 kg lighter, which allows for additional armour
• Smaller size, leading to a roomier turret
• Higher penetration
• Factory #9 was ready to produce D-10T guns along with D-10S

Points against the IS-100 in the same series of letters:

• D-25T is already sufficient against German tanks at all combat ranges
• Reduced caliber will reduce HE effectiveness against enemy fortifications and soldiers
• The increased ammunition capacity is negligible (29 rounds instead of 28)
• A large caliber, high rate of fire semi-automatic gun will lead to high concentrations of gases inside the tank

Additionally, in a report from the Chief of Experimental Machinery to the Chairman of the Technical Council, the superiority of the D-10T to the D-25T in armour piercing capacity is challenged:

"[The D-25T] penetrates a Panther frontally at 2500 meters, and that is not the limit. The 100 mm D-10T tank gun ... penetrates the front of the Panther at only 1500 meters, which is the maximum distance. ... The results are preliminary, as the D-10T has already fired 400 shells while the D-25T is new, but the difference is so drastic, that it is unlikely to change. "

The report explains this with the lower muzzle velocity of the D-25T: at such a large range, the heavy 25 kg shell has no problem penetrating the Panther's front, while its higher arc lets it impact the front of the Panther at a favourable angle. The D-10T's shells are faster, and therefore fly flatter.

The IS-5 was briefly a platform for very high velocity 85 mm ZiS-1PM (1000 m/s) and S-34-1B (1040 m/s), but those did not pass trials. From the same letter:

"Another question that is prompted by the experiments at Kubinka is the question of large muzzle velocities, namely of 85 mm guns with muzzle velocity of 1000-1100 m/s. Experience shows relatively poor effectiveness of the German 88 mm gun against the German Panther tank. At the same time, we know that such a gun would be of similar effectiveness to a 100 mm gun with muzzle velocity of 900 m/s. Work on these guns is conducted by TsAKB and factory #9, but their effectiveness against a real German tank is increasingly doubtful, especially considering that we cannot place this gun in a turret smaller than one that requires the D-10T or S-34 gun."

Moving on to the IS-6, its initial requirements were pretty lofty. Here are the project requirements:

CAMD RF 38-11355-2243

The mass was incredibly high compared to any IS tank before it, 65 tons. The armour was initially supposed to resist all German 75 and 88 mm guns, firing at up to 1500 m/s (I wonder where they managed to find those), but that requirement is struck out in the document. The tank was to be armed with a 122 mm gun, capable of 4-6 RPM, with one-piece ammunition. and 1100 m/s muzzle velocity. One 50 mm breech-loading mortar was planned (a feature experimented with on all IS tanks), but also crossed out. The tank would carry 35-40 shells for its main gun, 1500 rounds for its 7.62 mm coaxial machine gun, 500 rounds for its 12.7 mm AA machine gun, 1000 rounds for SMGs, 25 grenades, 27 signal flares, and 12 smoke bombs. All of this was planned to move at 40 kph, powered by a 1000 hp engine. 

The IS-6 didn't quite measure up to these requirements, but, several years later, the IS-7 did.