CHAPTER 2. A New Chassis
During the spring and summer of 1940, work was underway at the Kirov Factory and Plant No. 185 to design heavy SP guns based on the T-100 and SMK tanks. No final decision had yet been reached about the future of these two tanks. Plant No. 185 was struggling with the T-100 and vehicles based on it. In January 1940, Marshal G. I. Kulik had requested that a turret be developed for the T-100 to mount the M-10 152 mm gun. That version was designated the T-100Z. In April, designers at Plant No. 185 developed a project for a coastal defense tank based on the T-100. It was assigned the factory designation 103. It differed from the similar T-100Y project in that it had the B-13 130 mm naval gun in a rotating turret. Similar projects were also underway at the Kirov Factory: correspondence indicates that there were projects for mounting the B-13 130 mm naval gun and even the B-1-P 180 mm naval gun on an SMK chassis. Unfortunately, information about these projects is unavailable.
On June 11, 1940, a document appeared with the title “Proposals for Refining the Tank Armament System,” which also made mention of the following SP assault guns:
1. The KV tank must have a 76 mm gun with a muzzle velocity of at least 800 meters per second in order to have the capability of piercing 70–80 mm of armor. The gun must have a rapid-fire capability and a sufficient supply of rounds.
The gun currently most suitable for the purpose is the 76 mm antiaircraft gun model 1931. The tank must have armor between 90 and 100 mm in thickness.
2. The KV-2 tank must have a 107 mm gun with a muzzle velocity of 730–750 meters per second in order to be capable of penetrating 100–110 mm of armor. The gun should be capable of rapid fire, possess excellent penetration capability, have a sufficient supply of rounds, and fire a time-fuzed shell in addition to an armor-piercing projectile.
The most suitable gun type at the present time is the 107 mm M-60.
3. Have self-propelled, armored heavy artillery with the task of destroying reinforced concrete bunkers. As armament for the self-propelled turretless vehicle, use 122 mm, 152 mm, and 180 mm guns.
a) The most realistic way of solving this problem is to manufacture and mount a 100–130 mm gun on a tank chassis and equip it with an armor-piercing projectile capable of penetrating 130–150 mm of armor.
b) As a matter of urgency, build a prototype for mounting the 152 mm gun model 1935 (BR-2) on the SMK tank chassis and equip it with an armor-piercing shell system capable of penetrating 150–160 mm of armor and a concrete wall 1.5 m thick.
The gun must be protected by 60–70 mm of armor, and the entire system must weigh no more than 65 tonnes.
c) Mount a 180 mm gun on a turretless vehicle (the SMK chassis) and modify the suspension as needed and reduce the armor thickness in order to decrease the weight.
4. For the transition period, adopt the following solutions:
a) KV tanks—produce tanks armed with the 152 mm howitzer model 1938 (M-10).
b) The KV tank—produce tanks armed with the L-11 76 mm guns having rounds with normal propelling charges.
c) Immediately begin designing a chassis for the 76 mm antiaircraft gun model 1931 and the 107 mm gun (M-60).
d) Immediately begin production of the T-100 with the 130 mm gun and, as a matter of urgency, mount the 152 mm gun model 1935 (BR-2) on the SMK chassis.
e) Mount the 122 mm or 152 mm gun on the T-35 and test its added armor at the same time.
f) Have two types of T-34 tanks: a model equipped with the 45 mm gun and one equipped with the 76 mm gun. Improve the armor penetration of the 45 mm projectile and begin production of the F-32 or F-34 76 mm gun.
g) Arm all tanks with DS machine guns having thicker barrels capable of more prolonged firing than the DT.{1}
Note that the Kirov Factory’s brainchild was considered the highest priority platform for heavy SP guns. A note made by Military Engineer 3rd Class P. K. Voroshilov on June 27, 1940, bears eloquent witness of that fact (the adopted son of Marshal Kliment Voroshilov, he oversaw the development of Soviet heavy tanks):
Regarding the use of the tank as the chassis for super-heavy SP artillery, the most suitable model is the SMK. The arguments in favor of choosing it are that the SMK was the prototype for the KV tank, they have interchangeable suspensions, and parts of their transmissions are also interchangeable. Now, having worked backwards for commonality, we can achieve complete interchangeability of all transmission and suspension assemblies on both tanks.
This interchangeability will benefit tank production and cause no difficulty in supplying military units with spare parts.{2}
The future of the SMK and the T-100 had been conclusively decided by late June of 1940. The results of comparison tests made it clear that neither tank would enter the inventory, because there was the better-protected KV, which also weighed less. The “large-turret KV” emerged as a temporary solution to the bunker buster problem: mass production of tanks had begun in July 1940.
As mentioned above, the “large-turret KV” was a temporary solution to the problem of developing a heavy SP assault gun. The vehicle developed by Kurin’s team was essentially an oversized support tank like the BT-7 artillery tank (which is frequently called the BT-7A—but that designation belongs to a different tank). A major advantage was that the tank based on the KV chassis (designated the KV-2 in 1941) shared a great many common components with the base vehicle. It is worth noting that the KV-2 suffered from a large number of deficiencies. The KV chassis would only support a gun of limited power, whereas the military’s specifications called for a bunker buster equipped with the BR-2 gun. The small turret made it difficult to load the M-10T gun. In addition, having a rotating turret did not mean that the tank could fire at any angle.
After the SMK and T-100 programs ended, it was decided to concentrate on developing a heavy tank by upgrading the KV. The proposal for a new tank armament system introduced a number of changes: the 180 mm gun was abandoned in favor of the B-13 and BR-2 guns. On July 17, 1940, the Defense Committee under the Council of People’s Commissars issued decree No. 198ss giving the go-ahead to develop armored vehicles based on the KV chassis. According to this decree, the Kirov Factory was to manufacture the following vehicles:
a) KV tanks (T-220) with 100 mm of armor: one must be equipped with the F-30 85 mm gun, and the other with the F-32 76 mm gun;
b) Two prototype KV tanks with 90 mm of armor: one must be equipped with the F-32 76 mm gun, and the other with the F-30 85 mm gun;
c) One prototype vehicle armed with the BR-2 152 mm gun.{3}
The factory assigned the KV with 90 mm of glacis armor the factory designation 150 (the designator T-150 was used in correspondence of the Red Army’s Main Armored Forces Directorate [GABTU]). In November 1940, the tank served as the basis for a vehicle featuring the F-32 76 mm gun and a commander’s cupola. Plans called for this tank to replace the KV-1 in production under the designation KV-3.
The tank known as the 220 was very different from the KV. The hull was elongated and the number of road wheels on each side was increased to seven. A new turret with the F-30 85 mm gun was designed for the T-220. The 850 hp V-2F (V-10) engine served as its powerplant. This tank was completed on December 5, 1940.
The operational requirement for designing a 152 mm SP gun was issued in late August 1940. It should be noted that the operational requirement was signed only by Maj. Gen. Savchenko, deputy chief of the Main Artillery Directorate (GAU); GABTU chief Lt. Gen. Fedorenko did not add his signature to the document. The operational requirement was seven pages long. Therefore, only a portion of it will be quoted here:
I. General characteristics.
1. Vehicle type: tracked, armored
2. Total weight: not more than 55 tonnes
3. Dimensions: of a size allowing rail transportation in Western Europe.
4. Speed: 35 km maximum
- Maximum gradient on solid ground: 35°
5. Armament:
- BR-2 152 mm gun: one (with recessed rifling)
- DT machine guns: three (with one configured for antiaircraft fire)
- PPD pistols: two
- Gun depression angle: minus 3°; the machine-gun dead space must not exceed 10 meters
- Elevation angle: maximum possible
- The gun must traverse an angle of at least 10°.
- The machine-gun traverse angle must be at least 30°.
6. Combat load:
- 152 mm projectiles: 50
- Machine-gun cartridges: 3000
- F-1 hand grenades: 30
- PPD cartridges: 1000
7. Mobility:
- Gradient: at least 40°
- Side slope: at least 30°
- Vertical step: at least 0.8 m
- Trench: at least 3.0 m
- Ground pressure: not more than 0.70 kg/cm²
- Ford (unprepared): at least 1.5 m
8. Fuel endurance: at least 10 hours of engine operation
9. Crew: 8
- Provide a capability for the crew to move around inside the vehicle (without exiting it).
Note: the installation and design of the gun must allow for firing at a 20° angle of depression.
10. Communications equipment:
- For external communication: a shortwave quartz radio and a set of flags
- For internal communication: an intercom system at four locations (commander, driver, gunner, radio operator)
- A rod antenna that can be lowered alongside the vehicle from the inside
11. Armor protection.
- Armor thickness:
— Glacis: 75 mm
— Side: 60 mm
— Turret: 60 mm
— Roof: 30 mm
— Bottom: 40 and 30 mm
- The armor must be sloped at least 20°.
12. Engine: V-2K diesel engine supercharged to 850 hp.
13. Observation and aiming devices.
- In the turret, a PT-1 from the 45 mm tank gun and a new 6x telescopic sight with a 6–11° field of view.
- Mount a cupola for the commander with 360° visibility on the vehicle roof.
- Vision blocks with mirrors may be used.
- Provide the driver-mechanic with a vision block for forward vision and an optical device with a mirror in the vehicle roof for observation to the sides.
- Provide a vision block with a mirror for the radio operator.
- All vision devices must be designed to prevent projectiles, bullets, lead spray, and burning liquid from entering the tank through them.
- Provision must be made for replacing vision devices, their heads and lenses, and the crew must be able to safely clean them from inside the vehicle.
14. Special equipment:
a) The driver’s position must be designed for maximum comfort when driving the vehicle.
b) Locate the instrumentation for easy visibility by the driver and keep it to a minimum.
c) Provide protection for the driver against wind, dust, and rain when driving with the hatch open.
d) Use KV-type seats for the driver, radio operator, and all turret seats.
e) Power steering may be installed to facilitate driving.
f) Provide for cleaning and heating the air in the fighting and driving compartments.
g) Provide a gyrocompass for the driver.
h) Develop tools for facilitating the mounting of tracks, for removing the main assemblies and armor from the hull, and for self-recovery of the vehicle.
i) Develop a simple hoist for projectiles.{4}
The SP gun that the Kirov Factory was tasked to develop was assigned the factory designation 212 (it has often been called Object 212). The lead designer on the SP gun project was Ts. N. Golburt. This was the second vehicle with the same designation: a recovery vehicle based on the KV chassis had also developed under the designation 212. Therefore, the SP gun was often referred to as the 212A. Self-propelled gun 212 resembled an up-armored SU-14-1, especially in the arrangement of its fighting compartment. The chassis of the 212 was a reworked 220 (T-220) chassis with the engine compartment located in the center of the vehicle and the transmission and drive wheels in the front. The driver’s compartment was located in the bow, with only enough space for the driver-mechanic. The fighting compartment was located in a large superstructure at the rear of the vehicle. On the one hand, this design significantly increased the vehicle’s overall size; on the other hand, it improved crew comfort. In addition, placement of the superstructure at the rear made it possible to reduce the extent to which the BR-2 152 mm gun extended beyond the vehicle.
The sum allocated for development of the 212 was 2 million rubles. Of that amount, 100,000 rubles went for development of the engineering design; 25,000 for constructing the mockup; 300,000 for drawings; 75,000 for revising the drawings; 1,100,000 for manufacturing a prototype; 100,000 for testing; and 300,000 for maintenance. That figure did not include the cost of armament.
Plans called for manufacturing the SP gun prototype by December 1, 1940. However, it became necessary to make major adjustments to the plan. On December 10, 1940, the GAU’s Artillery Committee received a letter from the Kirov Factory signed by Zh. Ya. Kotin, head of SKB-2; P. F. Fedorov, head of SKB-4; and Ts. N. Golburt, the system’s chief designer. The letter contained a large number of comments on the operational requirement concerning issues that had arisen during design of the SP gun:
I. The vehicle weight of 55 tonnes stipulated in the operational requirement cannot be met with the armor specified for the following reasons:
1) The operational requirement states that the vehicle must be designed using the KV chassis and powertrain. The weight of these components, which totals 17,400 kg (excluding the engine with its fuel and cooling systems), cannot be reduced.
2) As installed on the vehicle, the BR-2 and its ammunition package weigh 17,600 kg.
3) The machine guns, ammunition, observation turret, seating, radio, fuel, crew, spare tools and accessories kit, etc., weigh 3000 kg.
4) Therefore, if the vehicle is to weigh 55,000 kg, the weight of the hull with (fixed) turret must be 17,000 kg.
The large size of the system results in the following hull dimensions:
Length: 7900 mm, width: 1920 mm, and height to top of turret: 2570 mm (from the bottom of the vehicle).
A weight of 17,000 kg is clearly not feasible for a hull of that size.
The size of the hull cannot be further reduced.
The hull of the SMK-1 may be taken as an example of a hull of similar size. Fitted with 60 mm of armor (side, glacis, turret), a bottom thickness of 30 and 20, and a roof thickness of 30, it weighed 31 tonnes (with turrets).
The armor thicknesses listed in the operational requirement are as follows:
- Glacis: 75 mm
- Side: 60 mm
- Turret: 60 mm
- Top: 30 mm
- Bottom: 40 and 30 mm
It is impossible to design a vehicle weighing 55 tonnes with a hull and turret weighing a total of 17 tonnes.
Our design is armored as follows:
- Side: 60 mm
- Glacis: 60 mm (slope: 30°)
- Lower front plate: 50 mm (slope: 45°)
- Lower rear plate: 50 mm (slope: 40°)
- Turret: 60 mm (slope: 10°)
- Bottom front: 30 mm
- Bottom rear: 20 mm
- Top: 20 mm
The weight of the vehicle without fuel, ammunition, and crew is 60 tonnes.
The combat weight of the vehicle is 65 tonnes.
At a weight of 65 tonnes, its ground pressure without armament is 0.83 kg/cm².
II. 1. In comparison with the BR-2 field gun, the laying rate is reduced by 33% in elevation and 10% in traverse.
The efforts required to operate the hand wheels are as follows: elevation: up to 10 kg; traverse: up to 8 kg.
2. The current recuperator mechanism design does not support firing at a depression angle of 3°.
3. The traverse angle is 4°, the same as the original field gun.
4. The combat load consists of 47 projectiles. There is no projectile hoist; there is a loading tray similar to the M-10 on the KV.
5. The vehicle’s dimensions fit within loading gauge “0”, and its corners come close to the limits for structure gauge “0”.{5}
The situation caused a heated debate in two directorates. Development of SP guns was overseen by the GAU, and the GBTU was frequently at odds with the artillerymen. In the case of the 212, the GAU oversaw work on the gun, and GABTU was in charge of the chassis. The artillerymen looked for various ways to solve this problem, as eloquently stated in a letter that M. M. Zhevannik, head of the second department of the GAU’s Artillery Committee, wrote on December 26, 1940, to Military Eng. 1st Class Komarov, chief of the Field Artillery Directorate’s Science and Technology Department (NTO UVNA):
Since vehicles are the responsibility of the NTO UVNA, the conclusion and report on the Kirov Factory’s letter should be written by NTO UVNA.
I hereby provide the opinion of the Artillery Committee’s second department on the issue:
1. Based on its preliminary engineering analysis, the Kirov Factory believes that the combat weight of the vehicle with the BR-2 gun will be approximately 65 tonnes instead of the 55 tonnes stipulated in the draft operational requirement.
In view of the fact that the maximum weight of a vehicle that may be loaded on a railcar must not exceed 60 tonnes and the weight of the vehicle without munitions, crew, and fuel will be approximately 60 tonnes, the Artillery Committee’s second department believes that a deviation from the specified weight (55 tonnes) can be accepted if a weight reduction of 2 tonnes is achieved by slightly decreasing the thickness of the turret armor.
A smaller weight reduction can be achieved by replacing the BR-2 with the BR-13 gun.
2. Without examining the design drawings, the Artillery Committee’s second department is unclear about the reason for reducing the traverse rate as compared with the BR-2 field gun.
3. We believe that the BR-2 laying devices should be used with just the attachment points changed.
In order to be capable of firing at depression angles on the order of -15–20° and retaining air in the recuperator while moving down a slope, we suggest that the Kirov Factory lengthen the tubes in the recuperator. The increased tube length must be such that air is still reliably retained at elevation angles on the order of 35°.
4. The 8° (+/-4°) traverse angle should be considered satisfactory.
5. The reduction in the number of rounds in the combat load from 50 to 47 is consistent with the draft operational requirement.{6}
All of the Kirov Factory’s suggestions were eventually accepted. According to the GABTU’s report on the project, assemblies for the 212 had been manufactured by January 1941. A manufacturing plant had also been developed for the SP gun and drawings had been sent to the Izhor Factory for manufacturing the hull. By that time, a total of 1.5 million rubles had been spent on the project. Work on the SP gun was delayed because the T-150 and T-220 had a higher priority, and there were also problems of a different nature. As of February 24, 1941, work on the “self-propelled object” had reached the following stages:
Drawings of parts, units, and assemblies are complete. Orders to manufacture the parts have not been sent to the shop and will not be sent until March 1, 1941. The hull and turret are in the production stage at the Izhor Factory and will be complete only on March 1, 1941.
The hull for the first SP gun was not received from the Izhor Factory until March 5, 1941. According to the report, assembly was delayed due to lack of parts. Meanwhile, a situation was developing at the Kirov Factory in the spring of 1941 that caused the 212 to gradually fade into the background. The Kirov Factory had received an urgent order to develop a heavy tank, which inherited the designation KV-3 from the T-150. This project, which received the factory designation 223, was developed from the T-220. The thickness of the glacis armor was increased to 120 mm, and it was given a new turret with the ZIS-6 107 mm gun. The combat weight of the KV-3 was estimated at 68 tonnes. Development of this tank was driven by intelligence about the appearance of a German heavy tank. The Kirov Factory also began designing the KV-4 and KV-5 heavy tanks. The combat weight of the KV-5 was 100 tonnes. All this was in addition to the fulfillment of plans for two other projects that were being pushed, the KV-1 and KV-2. With this workload, progress on the 212 came to a standstill beginning in the second half of March 1941. In both April and May 1941, progress reports on the “self-propelled gun based on the KV chassis” reflected “no change.”
The GABTU had somewhat different plans for the bunker buster. According to a GAU report on development work dated May 22, 1941, plans called for manufacturing 12 type-212 SP guns, with an estimated cost of 300,000 rubles for the BR-2 system. Somewhat later, the number of SP guns was cut back to 10 vehicles, and the cost of a system grew to 1 million rubles.
The decree “On Self-Propelled Artillery” issued May 27, 1941, by the Council of People’s Commissars and the Central Committee clearly demonstrates the serious nature of the plans for manufacturing an SP gun with the BR-2 gun. That document, which must have been signed by Joseph Stalin, said the following:
The Council of People’s Commissars of the USSR and the Central Committee of the All-Union Communist Party (Bolshevik) decree that:
I. The inventory of the Red Army shall include the following types of self-propelled guns:
1) SP bunker busters;
2) SP tank destroyers;
3) Assault artillery for supporting the mechanized infantry;
4) SP antiaircraft guns.
It shall also have special self-propelled vehicles for transporting ammunition and motorized infantry soldiers.
II. The following steps shall be taken to acquire these arms:
1. Bunker busters.
To carry out the decree of the Council of People’s Commissars of the USSR and the Central Committee of the All-Union Communist Party (Bolshevik), the People’s Commissariat of Heavy Machine Building shall deliver self-propelled 152 mm BR-2 guns on KV-3 tank chassis to the People’s Defense Commissariat during the following months:
August: 1 unit
September: 2 units
October: 2 units
November: 3 units
December: 2 units
shall provide the Kirov Factory hulls and armor parts for these vehicles one month prior to delivery of the completed vehicles to the People’s Defense Commissariat.
Within 20 days after receiving the first vehicle, the People’s Defense Commissariat shall subject it to testing.{7}
It should be noted that reference to the KV-3 as the base chassis did not mean the self-propelled gun had undergone a radical change. As mentioned above, the KV-3 was developed from the T-220, so the chassis change was basically a paper exercise. The May 26, 1941, operational requirement No. 1397 “for design of a 152 mm self-propelled gun” said as much. Here is a short quote from that operational requirement:
I. General characteristics.
1. Vehicle type: tracked, armored
2. Full combat weight with ammunition, fuel, water and crew: not more than 65 tonnes
Shipping weight: not more than 60 tonnes
3. The overall dimensions of the system on a railcar must be limited to 3500 mm in width and 5300 mm in height (from the rails); that is, the vehicle must not exceed the zero-gauge parameters.
4. Speed: 30 km/h maximum.
Maximum gradient on solid ground: 30°
5. Armament:
- BR-2 152 mm gun
- DT machine guns: two
- PPD pistols: two
- Angle of depression of the gun: minus 3°; the machine-gun dead space must not exceed 10 meters.
- Gun elevation angle: +15°
- Gun traverse angle: +/- 4°
Traverse angle:
- Rear machine gun: at least 30°
- Bow machine gun (radio operator): at least 15°
6. Combat load:
- 152 mm projectiles: 47
- Machine-gun cartridges: 3000
- F-1 hand grenades: 30
- PPD cartridges: 1000
7. Mobility:
- Gradient: at least 30°
- Side slope: at least 25°
- Vertical step: at least 0.8 m
- Trench: at least 3.0 m
- Ground pressure: not more than 0.85 kg/cm²
- Ford (unprepared): at least 1.5 m
8. Fuel endurance: at least 10 hours of engine operation
9. Crew: 7
- Provide a capability for the crew to change position inside the vehicle (without exiting it).
- Note: the installation and design of the gun must allow for firing at a 5° angle of depression.
10. Communications equipment:
- For external communications: a shortwave (10R), quartz radio and a set of flags
- For internal communication: an intercom system at four locations (commander, driver, gunner, radio operator)
- Rod antenna
11. Armor protection.
Armor thickness:
1) Glacis: 60 mm
2) Side: 60 mm
3) Lower front plate: 50 mm
4) Lower rear plate: 40 mm
5) Turret: 60 mm
6) Top: 20 mm
7) Bottom: 20 mm
The armor must be sloped at least 10° on the front and sides and -5° on the rear wall.
12. Engine: V-2K turbocharged diesel engine of 700–850 hp
13. Observation and aiming devices.
- In the turret, a PT-1 from the 45 mm tank gun and a KT-1 telescopic sight.
- Mount a cupola for the commander with 360° visibility on the vehicle roof.
- Vision blocks with mirrors may be used.
- Provide the driver-mechanic with a vision block for forward vision and an optical device with a mirror in the vehicle roof for observation to the sides.
- Provide a vision block with a mirror for the radio operator.
- All vision devices must be designed to prevent projectiles, bullets, lead spray, and burning liquid from entering the tank through them.
- Provision must be made for replacing vision devices, their heads and lenses, and the crew must be able to safely clean them from inside the vehicle.
14. Special equipment:
a) The driver’s position must be designed for maximum comfort when driving the vehicle.
b) Locate the instrumentation for easy visibility by the driver and keep it to a minimum.
c) Provide protection for the driver against wind, dust, and rain when driving with the hatch open.
d) Seats must be provided for the entire crew while the vehicle is in motion.
e) Power steering may be installed to facilitate driving.
f) Provide for filtering and heating the air in the fighting and driving compartments.
g) Develop tools for facilitating the mounting of tracks, for removing the main assemblies and armor from the hull, and for self-recovery of the vehicle.
h) Develop a folding tray to facilitate loading.{8}
In addition to SP gun 212, work also continued on a vehicle armed with the B-13 130 mm naval gun. This SP gun, later dubbed the SU-B-13, was first mentioned in a December 26, 1940, letter written by M. M. Zhevannik. Marshal Gregory Kulik also mentioned it in passing in an April 17, 1941, letter to Stalin, and he also discussed a different caliber for a similar SP gun:
Based on our analysis of the penetrability of the armor on Red Army artillery systems and the trends toward increasing armor protection of foreign tanks, I consider it urgent to increase the power of our antitank and tank artillery. To accomplish this, I believe we need to take the following actions:
<…>
III. Self-propelled guns:
To combat super-heavy tanks and bunkers, we must develop self-propelled guns with the following heavy artillery systems: the BR-2 152 mm gun, the B-13 130 mm gun, and the powerful new 107 mm gun. The BR-2 152 mm gun is capable of defeating 155 mm of armor at a 0° angle of incidence from a range of 2300 meters. The 130 mm gun can penetrate 130 mm of armor at a 0° angle of incidence from a range of 4000 meters, and the new 107 mm gun should penetrate 160 mm of armor at a 30° angle of incidence from a range of 1000 meters.
The 152 mm self-propelled gun has been developed, and a prototype is being manufactured at the Kirov Factory.
An elongated KV-4 tank chassis was used as the base vehicle.
The vehicle with the 152 mm gun weighs 65 tonnes.
The vehicle is equipped with armor 60 mm thick.
Under a February 7, 1941, decree issued by the Council of People’s Commissars of the USSR and Central Committee of the All-Union Communist Party (Bolshevik), the People’s Commissariat of Heavy Machine Building has been tasked with producing 10 vehicles mounting the BR-2 152 mm gun at the Kirov Factory this year.
The People’s Commissariat of Heavy Machine Building must be required to deliver the prototype of this self-propelled gun by June 1, 1941, and manufacture the remaining systems this year.
In addition, the People’s Commissariat of Heavy Machine Building must produce a prototype of the 130 mm self-propelled gun by September 1 and a prototype of the 107 mm self-propelled gun by October 1. The chassis used for the 152 mm system is also being used for these systems. A B-13 130 mm gun has already been delivered to the factory. The People’s Commissariat of Arms must be required to manufacture the new 107 mm gun’s tipping parts at Factory No. 172 and deliver it to the Kirov Factory by June 1941.{9}
In the spring of 1941, there were already two promising 107 mm antitank guns. In addition to the ZIS-24, which had been in development since 1940, work began on another gun in the spring of 1941. Its armor-penetration characteristics were as specified in Kulik’s letter. Factory No. 172 (in the city of Molotov, now Perm) was tasked with developing and manufacturing two antitank-gun prototypes. This system was assigned the designation M75. M75 development was headed up by the designer S. N. Dernov, and Factory No. 172’s chief designer, S. P. Gurenko, was responsible for overall management of the project.
M75 involved mounting a 170 mm barrel 70 calibers in length on the carriage of the ML-20 152 mm gun-howitzer. This gun weighed an estimated 7.5–8 tonnes, which drastically limited its mobility on the battlefield. The main mission of this antitank monster was to fight the heavy and super-heavy tanks that intelligence received from spies indicated Germany was producing.
On May 22, 1941, a plenary session of the GAU’s Artillery Committee reviewed and approved a draft operational requirement for a “special-purpose 107 mm antitank gun and the ammunition for it.” The operational requirement called for a muzzle velocity of 1020 m/s and a capability to penetrate 160 mm of armor at a 30° angle of incidence from a range of 1000 meters. In addition, the gun was to be mounted on the carriage of the ML-20 152 mm gun-howitzer, which was clearly a plus for Factory No. 172. The length of the barrel was not to exceed 70 calibers, and it was to be capable of firing 10 rounds per minute. The system was estimated to weigh a total of 8000 kg.
No project to mount the 107 mm antitank gun on the KV chassis similar to the 212 or the SU-B-13 was in the works—not even at the operational requirement level. While the leaders were thinking up new types of weapons, the artillerymen were working on current projects. They completed the M75 prototype by July 1941, and the gun entered factory testing that same month. It should be noted that, unlike its counterparts, Factory No. 92’s design bureau had not progressed beyond design work in July because it was heavily engaged in other projects. Problems with manufacturing the required number of 107 mm shells and higher priority tasks made it necessary to temporarily scale back work on the heavy antitank gun.
M75 testing continued into 1942. By that time, however, there was no longer a need for the antitank monsters. The super-heavy German tanks had not materialized, and, in addition, the actual M75 parameters did not meet requirements for a variety of reasons. Work on the gun was put on hold, but it came up again in 1943 when the heavy German tanks eventually made it to the front.
In contrast to the 107 mm SP gun, the B-13 project with the 130 mm gun was listed in GAU development plans dated May 22, 1941. A proposal in 1941 called for production of 12 SP guns of that type, at a cost of 300,000 rubles each. The specifications for the SU-B-13 can be found both in a letter written by Kulik and in a draft operational requirement dated June 16, 1941:
I. General characteristics.
1. Vehicle type: tracked, armored
2. Total weight: 55 tons
3. Armament: the B-13 130 mm gun and 3 DT machine guns
4. Combat load: rounds for the gun, 100
- Machine-gun rounds: 2500
- Hand grenades: 30
5. Armor:
- Glacis: 30 mm
- Side: 30 mm
- Top: 30 mm
- Bottom: 20 mm
6. Crew: 7
7. All of the vehicle’s remaining dynamic characteristics and its mobility are to be the same as the KV-4 tank. The engine mount, transmission, and suspension system must be the same as those used on the KV-4.
8. The vehicle’s dimensions must allow shipment by rail.
9. SU-B-13 artillery system specifications:
a) The artillery system must be installed on a production chassis without a turret, and the crew must be protected against diving aircraft.
b) The angle of traverse must be at least +/-10°.
Elevation +20° to 25°
-2° to -3°
c) The layout of the artillery system, aiming devices, and ammunition rack must enable at least three aimed shots per minute.
d) The vision devices must provide good visibility from the vehicle, and a commander’s cupola enabling 360° vision must be installed.
e) The vehicle must support firing from cover.
f) The artillery system must have a means of securing the gun in travel position.
10. Communications equipment:
a) A KRSTB radio must be provided for external communication. A TPU-4 intercom system must be installed for internal communication.
b) Provide for stowage of 2 telephone sets and 2–3 km of wire.{10}
Unlike the 212, the SU-B-13 was not a bunker buster. The specifications clearly describe a heavy tank destroyer that was developed in a rush to combat German heavy and super-heavy tanks. This is clearly evident from the rate-of-fire requirement and the requirement for 30 mm of armor, the same armor thickness as on the SU-34 tank destroyer based on the T-34 and the A-46 tank destroyer based on the A-42 prime mover, which were developed by Kalinin Factory No. 8 (in Kaliningrad, a city now named Korolev). The identification of the KV-4 as the base chassis is an error. Records show that this is what Kulik called the KV-3 (Project 223), confusing it with the KV-3 (Project 150, or the T-150), which originally was supposed to go into production. Because the Great Patriotic War began a week after the operational requirement was drafted, the SU-B-13 did not make it past the conceptual design stage.
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