Category: WW2 Soviet SPG Prototypes

Soviet Union (1940-1941)
Heavy Self-Propelled Gun – Only Components Built

Even after the KV-2 entered service with the Soviet military, its mediocre concrete penetration still left the Soviet artillery units craving for a more powerful bunker buster after the encounters with the Finnish Mannerheim Line. Development would lead to the Object 212 SPG, but due to the start of the war with Germany and no immediate need for such a vehicle, progress would slow down until it was canceled completely.

Cracking the Mannerheim Line

The Winter War (November 1939 – March 1940) between the Soviets and Finnish taught both sides a series of lessons on fighting a modern war. For the Soviets, this meant incorporation of armor and penetrating the heavily fortified lines of the Mannerheim defensive line on the Karelian Isthmus. Its construction began in the early 1920s, but those segments were poorly built and out of cheaper materials, such as wood. A second plan of building the line started in 1932, which included concrete bunkers with underground sections. Fixed gun mounts of various calibers, trenches, and traps, such as anti-tank pyramids and barbed wire, were meant to funnel attacking troops towards well dug-in defenders. These defensive features combined with the marshy area, with either bogs, lakes or thick forest in winter time, posed a difficult fighting area for the attacking Soviet troops. The line managed to delay the Soviets for a few months.

The biggest problem were the “millionaires” (hinting at the cost), as the Soviets would call them, which were large, complex, and thickly armored bunkers built in the period before the war. For combating these, the most effective way was artillery fire from the massive 152 mm BR-2 howitzer, capable of penetrating 2 m of concrete. However, the system was incredibly large and cumbersome. Transporting the tracked howitzer through the rough terrain was a logistical nightmare.

The 1930s were a period of considerable maturing of the Soviet armored forces, and the Winter War would be a great testing area for various Soviet tanks, such as the serially built T-26, T-28, and BT-series light tanks, but also various prototype and projects built for the needs created by the war, such as the Object 217 (PPG), SMK, T-100, and KV tank. The KV (U-0) specifically would see action in December 1939. The tank was armed with a main 76 mm L-11 gun and a secondary 45 mm one in a small turret, which was removed on serially produced tanks. After unpleasant experiences with Finnish fortifications, on 11 January 1940, the Leningrad Kirov Plant (LKZ), the builder of the SMK and KV tanks, was asked to develop a tank mounting the M-10 152 mm howitzer. The conversion was made by developing a larger turret on the KV with the M-10T howitzer (the T meaning that the gun was adapted for use in an AFV). It was originally just called KV with a big turret, but was later named KV-2. Several prototypes/early vehicles of the KV-2 would see service against the Finns.

Early Bunker Busters

While the KV-2 was being tested in battle, on 17 January 1940, a decree from the Soviet Defense Committee was signed. Plant No.185 was also tasked with continuing their projects on the SU-14 by installing the 152 mm BR-4 inside. The SU-14 was a troubled self-propelled gun project dating back to summer 1933, but due to various reasons, only two were built and tested. The project involved taking the two open-topped self-propelled guns based on the T-35 heavy tank and armoring them, giving them the capability for direct fire from closer ranges, though it was estimated that the average combat range would be between 1.5 to 2 km. The vehicles were given up to 60 mm of armor frontally, increasing the total weight to 64 tonnes, and were renamed to SU-14-2. Despite the progress, the Izhora Plant was only able to deliver the first vehicle by 13 March, a day before the end of the Soviet-Finnish War. The two vehicles were still tested at Kubinka and would partake in the defense of Moscow, but would never enter mass-production.

During the same period, Plant No.185 would not only upgrade its previous SPGs, but also design new vehicles. Their T-100 tank, a competitor to the SMK, would become the basis for heavy gun carriers. Firstly, as a response to the KV-2, the T-100 was fitted with a larger turret and M-10T howitzer and named T-100Z. Additionally, three other projects based on the T-100 were designed to equip the 130 mm B-13 gun, which had a lighter and faster firing shell with similar ballistics. The first two were the T-100X and T-100Y, which replaced the two turrets of the T-100 with a large fixed casemate. The T-100Y was to be built, but it was delivered by the Izhora Plant only on 14 March and thus would not be tested against Finnish “millionaires”. The third project, T-103, was meant to equip the B-13 gun in a large turret, but the project was abandoned after a mock-up was built.

Development

The conclusion of the Winter War marked the end of the immediate need for heavy bunker busting vehicles, but they were still seen as a long-term necessity. Thus, on 10 April, testing of the Factory 185’s SU-14-2 and T-100Y commenced. However, due to the archaic chassis of the SU-14 and failure of the T-100 heavy tank, both self-propelled guns were doomed. Attention shifted back to LKZ, and while the KV-2 was a quickly designed vehicle that was forced into service before it was properly tested, it was far from what the Soviet artillery forces needed. The M-10T howitzer had mediocre concrete penetration, 900 to 1,140 mm of reinforced concrete from 1,000 m distance.

On 17 July 1940, LKZ would be tasked with developing a series of new heavy tanks based on the KV tank. In total, there would be four heavy tanks, with 90 mm to 100 mm of armor, as well as being armed with 76 mm and 85 mm main guns. Additionally, a heavy self-propelled gun was also requested, based on the chassis of these new heavy tanks, and armed with the 152 mm BR-2 howitzer.

These heavy tanks would become the T-150, T-220, and T-221, the first two which were built in the fall of 1940 and tested in January-February 1941. The T-220, which was a lengthened KV-1 (seven roadwheels) and 100 mm of armor all around would become the basis for the self-propelled gun.

It is worth mentioning that, during the same period, the mounting of large caliber howitzers (122 mm, 130 mm, 152 mm, and 180 mm) on the chassis of the SMK was also explored, as a document from 11 June specifically requested the 152 mm BR-2 be mounted on the SMK. Likewise, the idea of mounting the 152 mm BR-2 on the T-100Y was also raised, but by summer 1940, both the SMK and T-100 chassis were dead for good and these plans never went past proposal stages.

On the other hand, the KV-1 and KV-2 would enter full-scale serial production in June 1940 after the implementation of the “Stalin Task”, which demanded the yearly production of 230 KV tanks (130 KV-1s and 100 KV-2s). It seemed as if the KV chassis was the optimal choice for a heavy bunker busting SPG, and there were doubts even about the development of such a vehicle, considering the expected high numbers of KV-2s in the upcoming future.

Development of the self-propelled gun started in August-September 1940 at SKB-4, the LKZ artillery design bureau, headed by P.F. Fedorov, who appointed Ts.N. Golburt as the chief engineer of the project. Design of the hull was done at the SKB-2 design bureau instead, as they had more experience with heavy tanks and designed the KV-220. The self-propelled gun would be based on the Object 212 artillery tractor, and would receive the same name, though some modern resources add the suffix “A” at the end (Object 212A) to make the distinction, though this was never official.

Object 212 Tractor

The original Object 212 tractor was a proposal designed between January and February 1940. It was a 35-tonne recovery tractor on a heavily modified KV chassis, meant to tow knocked-out tanks, as well as for supply and logistics support. The project was never approved for production. It was designed at the SKB-2 design bureau with chief engineer N.V. Khalkiopov. Early blueprints, from 9 February, show that the tractor was to have the final drive towards the front of the vehicle, with the 3 man crew and engine in the center. The rear was reserved for a flatbed for storage. Although derived from the KV tank, all of the components were unique, from the running gear and return rollers, to the hull.

However, by May 1940, the design was changed to use an inverted KV-1 hull, with KV-1 components. The driver was moved to the extreme left of the hull, to allow for the engine and driveshaft. Other small differences, such as the addition of a sprocket guard, were added. Sometime thereafter, a full-scale wooden mock-up of the hull was built. The same general layout was kept as on the earlier tractor. The Object 212 tractor was canceled after the SKB-2 transition to ChTZ.

Further Development

The technical drawings of the 212 SPG were completed and signed by Kotin on 5 November, but the 1 December deadline set by the GABTU (Main Directorate of Armored Forces) was not met. Furthermore, LKZ officials Goldburt, Kotin, and P.F. Federov sent a ‘complaint’ letter to the GABTU Artillery Office on the topic of the technical requirements. Firstly, they claimed that keeping the vehicle at a weight below 55 tonnes while still packing 75 mm of frontal armor was not possible. Alternatively, they proposed that the weight threshold be increased to 65 tonnes, but still the vehicle would only receive 60 mm of frontal armor. The Artillery department had to back down and accept these measures.

In a letter dated December 1940 from Major General Slavchenko, Deputy Chief of GABTU, to Lieutenant General T. Fedorenko, Chief of the GABTU, reported the status of self-propelled gun developments at LKZ. Firstly, the first prototype of the Object 212 SPG was projected to be finished by April, with 12 units built by 1 October. Secondly, the mounting of the B-13 130 mm gun on a SPG chassis (likely the same as on the Object 212) was also mentioned, with the first prototype to be complete by 1 May and 12 pieces to be built by 1 November. The 130 mm naval B-13 which had previously been mounted on the T-100 series of heavy SPGs would now get a second chance, being mounted on a KV chassis.

The project of the 212 SPG was completed by January and the drawings and documentation were sent to the Izhora Plant for prototype manufacturing. By 5 March, the Izhora Plant started to deliver components from the same batch as the two T-220 and T-221, but assembly was delayed in a sudden turn of events.

On 11 March, the Soviet intelligence services submitted a report on German tank developments, which included the alleged design of a Mark VII heavy tank, with 105 mm gun and 90 tonnes of weight (Pz.Kpfw.VII Löwe). Other heavy tanks included the Mark V and Mark VI heavy tanks, with weights of 36 and 45 tonnes respectively. The Soviet officials scrambled towards designing a Soviet equivalent, and thus the KV-4 (Object 224) began its development, with a weight of 75 tonnes and 107 mm main gun.

On 7 April, more heavy tanks were proposed, namely the new KV-3, also known as Object 223, which used the hull of the T-221 (up-armored to 120 mm) and an entirely new turret and 107 mm gun. Lastly, a 100 tonne heavy tank with 170 mm of frontal armor was also requested, the KV-5 (Object 225).

As the new KV-3 was to essentially replace the T-220, while still having an nearly identical hull (the only difference was the 120 mm of armor instead of 100), the Object 212 SPG would now reuse the hull of the KV-3, though no major changes were required.

From Bunker Busting to Lion Hunting

In wake of the German heavy tank developments, Marshal of the Soviet Union G.I. Kulik would send a letter on 17 April to Stalin. Kulik, who was supervising work at LKZ, claimed that the BR-2 gun on the Object 212 in development could be used against heavily armored tanks effectively, penetrating 155 mm of armor at 2,300 m. Likewise, he mentioned the development of the self-propelled gun armed with the 130 mm B-13, but this time on the lengthened chassis of the KV-4. An unspecified high-power 107 mm gun was also under consideration.

It must be noted that the KV-4 Marshall Kulik mentions was likely a mistake or confusion on his part and could not have been the KV-4 super heavy tank, the design of which was not completed until early May. The two SPGs with 130 mm and 107 mm guns were to be built by 1 September and 1 October respectively. This is confirmed at the end of Kulik’s letter, which states that the two tank destroyers were to use the same chassis as the 152 mm howitzer variant (Object 212). Lastly, Marshall Kulik mentions that the original Object 212 prototype would have to be finished on 1 June, allowing for production for the remainder of the year. Another option is that Kulik simply misspelled or confused the KV-3 and KV-4. Realistically, the KV-4 would wind up being so large there was no point in enlarging it for mounting these bigger guns. Likewise, an SPG based on it would have weighed far more than 55 tonnes, considering that the heaviest KV-4 design, by G.V. Kruchyonyh, weighed 107 tonnes, and the lightest, designed by N.L. Dukohv, weighed ‘just’ 82.5 tonnes.

The SPG armed with the 130 mm B-13 was to have a weight of 55 tonnes and thus be lightly armored, at only 30 mm all around the casemate, with adequate protection against shrapnel and diving aircraft attacks. This vehicle is commonly known today as the SU-B-13, though it was not an official name.

The other vehicle was also meant as a tank destroyer and to be equipped with an unspecified high power 107 mm gun, likely the ZiS-24 or M-75, but the vehicle never went past the proposal stage.

Regarding developments on the Object 212, activity was stagnant from March to April. On 27 May, it was confirmed that the 212 SPG would now use the KV-3 (Object 223) chassis instead of the T-220. Whether this means that the Object 212 SPG would have inherited the KV-3’s 120 mm of hull armor as opposed to the original 100 mm on the T-220 is unknown. Delivery of the first prototypes was once again postponed to August, with 12 vehicles to be built and later cut down to 10.

On 30 May, a report on the costs of KV heavy tank projects was published, and here, the 212 SPG was mentioned. In total, it cost 2 million rubles, the equivalent price of four KV-1 mod.1941 tanks.

Stage of Object 212 SPG Development	Price (thousands of rubles)
Draft drawings	100
Scale models	25
Technical drawings	300
Prototype construction and factory trials	1100
Proving ground trials	100
Drawing correction after trials	75
Repair of prototypes and improvements	300
Total cost	200

Source: CAMD RF 38-11355-101

Design

The design of the Object 212 self-propelled gun was very different from any previous vehicles, as it was based on the combination of 212 tractor and the T-220 heavy tank. As remnants of the 212 tractor, the engine and final drive were in the front of the hull, with the idler towards the rear. The platform that was previously used for transport was lengthened, as the chassis was now borrowed from the T-220, and fitted a very large armored casemate, housing the crew and the BR-2 howitzer.

The vehicle is claimed to have resembled the SU-14 in terms of general design, but it might just be pure coincidence. Mounting a large howitzer and its crew towards the rear of the hull offers more internal room, better recoil management, and less frontal gun overhang.

Crew

The exact crew details were never specified, but based on the type of vehicle, at least seven men were required: commander, driver, radio operator, two gunners, and two loaders. Although the BR-2 field howitzer used a crew between 10 and 15 men, a lot of this manpower went to preparing the vehicle for transport, ammunition supply, and other logistical difficulties, which would not exist on a self-propelled chassis. Furthermore, a larger crew would have been unbearable in the large, but enclosed casemate.

The driver was positioned to the extreme left of the chassis, to the left of the driveshaft, as opposed to the center on the KV-1, due to the engine and driveshaft now occupying a large volume inside the hull. The radio operator likely sat behind the cooling system and operated a 71-TK-3M radio. The tank commander and the gun operators would stand in the casemate. The commander would have a slightly elevated ‘cupola’ with a PTC rotating periscope for vision, to the right of the gun. The main gunner would sit on the left side of the gun and had 3 fixed periscopes, main gun periscope, and a PTC rotating periscope, for a total of seven periscopes in the casemate. For self-defense, four firing ports were made on the side walls and one 7.62 mm DT machine gun was mounted in a ball mount on the rear wall. For entry and exit, two to three hatches were mounted on the top, as well as a door on the rear wall, for easy entry/exit and ammunition resupply.

Propulsion

The 212 SPG had a V-2SN, a centrifugally supercharged variant of the standard V-2 12-cylinder diesel engine, outputting 850 hp. It was developed by Plant No.75 for the T-220 heavy tank. During its testing on the tank in January-February 1941, the engine was still unfinished and would prove to be a disaster. It lasted for 5 hours and 51 minutes or 106 km on the nearly 63 tonne heavy tank, the tank reaching a top speed of 21.2 km/h. Fuel consumption was 15.5 liters per hour or 0.83 l per 1 km. Wearing out of the pistons squirted hot oil and led to power loss, stopping the trials. Due to the lack of a spare engine, the trials were terminated.

The 700 hp V-5 mounted on the T-150 would suffer a similar fate, but with slightly better results. Due to the engine plant’s inability to provide engines for the new heavy tank projects, the trials of the T-150 and T-220 were postponed until Plant No.75 could fix these issues.

The KV-3 (Object 223) heavy tank, which would become the chassis for the 212 SPG when the T-220 was canceled, was also meant to equip the same engine.

The fuel tank capacity on the 212 SPG was of 845 liters, for an estimated road range of 200 km.

Main Armament

The most important element of a self-propelled gun is its main armament. For the Object 212 SPG, this was the 152 mm BR-2 Model 1935. The field gun counterpart was particularly controversial. It weighed over 18 tonnes, had a maximum road speed of 15 km/h, and took a 15 man crew 25 minutes to set it up from marching position into firing position with maximum firing elevation. Additionally, by the start of the invasion of the USSR, only 37 pieces had been built, of which only 27 were in active service. Other concerns were the poor horizontal traverse of just 8° towards each side and 100 round barrel life. The latter was fixed in 1937 with deeper riflings. The gun would still see intensive use, from the Siege of Leningrad all the way to shelling Berlin. After modernisations in the 1950s, the guns would be used all the way into the 1970s. The rate of fire was a standard 1 to 2 rounds per minute and maximum range was around 25 km.

The advantages of mounting this cumbersome but otherwise very powerful gun on a tank chassis were obvious, hence the Soviet Artillery department’s wishes for one. The low towing speed and long setup time could be vastly improved, while the thick armor of the vehicle would allow for flexibility in operation, whether it would be close-range support or indirect fire.

However, the mounting of the gun inside an enclosed casemate would have certain negative side effects. Firstly, the tight operating space could have decreased rate of fire and made it a cramped space to be in, but still better than being exposed to the elements and enemy counterbattery. Additionally, as seen on the SU-14, a casemate significantly decreased the elevation angle of the gun, from 60° to 30°, while in the case of the Object 212 SPG, it decreased to just 15°, making indirect fire virtually impossible. This was not seen as an issue, as the vehicle was meant for direct fire support. Gun depression was -3°.

The vehicle was equipped with a respectable 47 two-part rounds for the main gun. In comparison, the SU-152 had 20 rounds. The shells were stowed in the rear corner of the vehicle floor, as well as on the casemate sides. Loading was assisted by a bracket for resting the rounds on. Ammunition for the single 7.62 DT machine gun was 3,000 rounds.

Comparison chart of the KV-2 and Object 212 SPG main guns
Name	M-10T	BR-2
Caliber	152.4 mm	152.4 mm
Muzzle velocity m/s	400-500	880
Shell weight	40 kg	49 kg
Explosive weight (kg TNT)	5.3-5.8	6.5 -7
Penetration (armor)	72 mm @ 60° from 1,500 m	155 mm from 2,300 m
Penetration (reinforced concrete)	900-1,140 mm from 1,000 m	1,500 mm

Br-2 152 mm Howitzer on Turreted KV Chassis

Sometime during spring 1941, Kotin, with SKB-2 engineers L.E. Sychev and A.S. Ermolaev, went on a day trip to study naval guns of ships at the Baltic Fleet. There, they inspected the battleship Marat and a Kirov-class cruiser, as well as various other ships. Several systems were analyzed, including gun mounts, loading systems, and ammunition stowage mechanisms. The goal was to incorporate naval guns on tank chassis. One of these projects was mounting the Br-2 152 mm howitzer inside an armored turret and onto a KV chassis (likely also KV-220/KV-3).

Unfortunately, not much is known about this project, aside from the recollections from SKB-2 engineer, K.I. Buganov:

“Before the war, we worked on a hull for a self-propelled artillery installation based on KV with the placement of a 152-mm Br-2 naval gun in its armored turret. The car turned out to be two tons heavier than the calculated one, and Joseph Yakovlevich asked me: “Do you have any proposals for weight reduction?” I said, if you reduce the distance between the engine and the gearbox, you can reduce the length of the car by 500 mm. Reduce the length of the sides, roof, bottom, tracks, and this will give great weight savings. Joseph Yakovlevich said only one word “good”, and then instructed to rework the drawings, regardless of the fact that tracing papers had already been released, that is, essentially the work had ended. Joseph Yakovlevich always quickly grasped the main thing, and if he saw a technical benefit, he never stopped before the difficulties of rework.”

Unfortunately, no drawings of the vehicle are known to survive. The project likely did not survive summer 1941, and was undoubtedly a very challenging feat to fit the Br-2 in a rotating armored turret and still be capable of firing.

Fate

The German invasion of the Soviet Union on 22 June did not have much effect on the 212, which had effectively been frozen in development for nearly 5 months. An attempt to cancel the project would infuriate the head of the Artillery Department, Colonel-General V.I. Khoklov, which after one-and-a-half years, still did not get an improvement over the KV-2 in terms of direct fire bunker busting.

By August, the German forces were approaching Leningrad, the city where LKZ was based and so most of the engineers and projects were transferred to ChTZ in Chelyabinsk, which would be renamed to ChKZ (Chelyabinsk Kirov Plant). Some tank projects were canceled, like the KV-4 and KV-5, while the KV-3 was to continue development at ChTZ. The prototypes of the KV-220 and T-150 would be pressed into combat service at such a desperate time.

The Object 212 had a different fate. It was transferred to the Ural Heavy Engineering Plant (UZTM) in modern day Yekaterinburg. The design bureau, headed by F.F. Petrov, had plenty of experience on artillery pieces and just started producing KV-1 tanks as a subcontractor to ChTZ. On the other hand, this was their first encounter with a tracked SPG project. A.S. Ryzkhov was appointed Head of the Object 212 project.

In October, UZTM sent a letter to ChTZ requesting material and components of the KV-3 to be able to start concrete work on the 212 SPG. The problem was that ChTZ was not working on the KV-3, which had been transferred from LKZ, but it was frozen.

The Object 212 would have its final breath in November 1941, when it was noticed that the switch from tractor production to KV production at ChTZ would mean no more tractors to tow artillery, and thus self-propelled guns were necessary, of which the Object 212 was first mentioned.

However, by December 1941, the KV-3 was virtually canceled and focus at ChTZ went towards other vehicles. Without the enlarged hull of the KV-3, UZTM could not build a prototype and the project was canceled as well.

Interestingly, in March 1942, Experimental Plant No.100 was appointed to design and develop a 152 mm BR-2 heavy self-propelled gun on a KV chassis, the bunker buster. Plant No.8 was responsible for the gun mount. 1,500,000 Rubles were assigned to the project, but the death of the KV-3 and complexities of lengthening the KV-1 chassis doomed it as well.

Various heavy self-propelled gun designs on KV chassis would be drawn out in the following period by several design bureaus, but it was not until 1943 that the Soviets could field one, in the form of the SU-152, armed with the ML-20S 152 mm howitzer mounted on the KV-1S chassis.

Conclusion

The Object 212 was a very promising project on paper. The ability to improve the BR-2 howitzer’s main drawbacks and mount it on an armored chassis would have proven very beneficial. However, the project was on a rough route right from the start. The end of the war with Finland meant that there was no immediate need for such a vehicle, while the mass-production of the KV-2 could (on paper) fulfill the same role already. Lastly, the vehicles it was intended to be mounted on, the T-220 and KV-3, were too heavy and unreliable, and with the start of the war with Germany, the Soviets could not afford to spend time and resources on uncertain projects. The need for a self-propelled gun armed with a potent 152 mm howitzer would persist well into the war, until the SU-152 would enter service.

Object 212 SPG Specifications
Dimensions (L-W-H) (approx.)	7.90 x 1.92 x 2.57 m
Total weight, battle-ready	65 tonnes (50 tonnes without ammunition, fuel and equipment)
Crew	7 (Commander, driver, radio operator, 2x gunners, 2x loaders)
Propulsion	V-2SN 12-cylinder supercharged diesel, outputting 700 hp.
Speed	35 km/h hypothetical
Suspension	Torsion bar, 7
Armament	152 mm BR-2 howitzer Single 7.62 mm DT machine gun
Armor	Front: 60 mm (75 mm originally) Sides: 60 mm Rear: 45 mm Roof: 20 mm Belly: 20-30 mm
	Some components built

Sources:

Breakthrough tank KV – Maxim Kolomiets
Supertanki Stalina IS-7 – Maxim Kolomiets
Victory Tank KV Vol.1 & 2 – Maxim Kolomiets
Constructors of Combat Vehicles – N.S. Popov
Domestic Armored Vehicles 1905-1941 – A.G. Solyakin
Bronevoy Schit Stalina. Istoriya Sovetskogo Tanka (1937-1943) – M. Svirin
Heavy Tank KV – M. Baryatinsky
About the forgotten creators of Soviet armored power. (historyntagil.ru) – S.I. Pudovkin
Pillbox Hunter | Warspot.ru – Yuri Pasholok
Вторая жизнь устаревших шасси | Warspot.ru – Yuri Pasholok
КВ-3: набор танковой массы | Warspot.ru – Yuri Pasholok
Опытный танк с боевой биографией | Warspot.ru – Yuri Pasholok
The history of the Mannerheim Line, part 2 (winterwar.com)
Tank Archives: Heavy Trials – Peter Samsonov
Tank Archives: Heavy Tank Costs – Peter Samsonov
Tank Archives: Kirov Factory Prototypes, March 1941 – Peter Samsonov
152-mm gun Br-2 model 1935. USSR (victorymuseum.ru)

Soviet Union (1931)
Experimental Self-Propelled Gun – At Least 2 Prototypes Built, Possibly A Small Production Series

During the 1920s, the Soviet Army was rather poorly armed and equipped. As it was slowly built, the need for armored vehicles, such as tanks, arose. The initial attempt to develop domestic tank design failed, as the Soviets lacked experience in designing such vehicles. For this, a military delegation was dispatched to countries, including the United States and Great Britain, in hope of acquiring a foreign design that was to be built under licenses. From Britain, the license for the Carden-Loyd tankette was acquired. The Soviets further improved this design, which led to the creation of the T-27 tankette. As it was only armed with a machine gun, the Soviets wanted to increase its firepower by adding a 37 mm gun, creating a small series of experimental vehicles.

The T-27’s Brief History

During the 1920s, the Soviet armored forces were in a process of reorganization and rearmament. Initial Soviet attempts to develop armored vehicles were rather unuseful, and only smaller series were built. The first domestically built tank, the T-18 (MS-1), was adopted in small numbers to service in July 1927. Soviet industry was experiencing constant delays in delivery and poor quality of production. In November 1929, Управление по механизации и моторизации – YMM (English: Department of Mechanization and Motorization – UMM) instructed that the current development situation was unfeasible in the near future. To remedy this situation, YMM was instructed to seek technological help abroad.

On 30th December 1929, a commission led by the head of the UMM, Innokentii Khalepskii, went abroad. The plan was to visit Czechoslovakia, France, Germany, Great Britain, and US in order to purchase technologies and armaments. The negotiation with Great Britain proved most promising, as the Soviets managed to purchase a few different tank designs, including the Vickers Carden-Loyd tankettes, the Vickers-Armstrong 6-ton, and the Mk.II medium tanks.

Some of the newly acquired Carden-Loyd Mk.VI tankettes were sent to Zavod No.37, a factory in Moscow. There, an engineering team led by N. Kozyrev examined this vehicle in great detail, in order to be put into production as quickly as possible. The Soviet engineers were generally satisfied with this vehicle, but noted a number of shortcomings. Consequently, they implemented a series of improvements (such as modifications to the suspension, adding a stronger engine, etcetera) before the vehicle under the name T-27 was finally accepted for service.
The T-27 was basically a two-man tankette armed with one DT 7.62 mm machine gun. Its production began in 1931, and by the time the production stopped in 1933, slightly fewer than 3,300 had been built (the precise number differs greatly between sources). Given their obsolescence, the T-27 did not stay long in active service, as it was replaced by much more modern tank designs. The T-27s were allocated for crew training, but during the Axis invasion of the Soviet Union in 1941, many would be put into service. They performed poorly due to their weak armament and armor.

Improving Firepower

While the T-27 filled the gap of a lack of armored vehicles, its potential combat effectiveness was limited due to its weak armament and its general configuration which lacked a turret. As they were available in great numbers, discarding them was not a proper solution. On the other hand, increasing their overall combat performance by adding new armament was something that the Soviet Army considered doing.

For this reason, in October 1930, an official order was issued that such modification be implemented. The following year, a design team led by K.K. Sirken from the Leningrad Bolshevik, began the first steps to do exactly that. The overall T-27 design was to remain the same, with the exception of the vehicle’s right superstructure, where some modification would be required in order to fit the larger gun. This would lead to the creation of two prototypes. These received slightly different armament rearrangements. In addition, the first prototype used a four-wheel suspension, while the latter used the more common six-wheel suspension. Due to the rather short development time, this project appears to have received no official designation.

Design

Hull

The hull of this vehicle could be divided into three compartments or sections. The front-mounted transmission with the drive unit, the central engine compartment, and the two fully enclosed crew positions (opposite of the engine).

Engine

The engine from this T-27 modification was unchanged. It was powered by a Ford four-cylinder petrol, water-cooled engine delivering 40 hp @ 2,200 rpm. The T-27’s maximum speed with this engine was around 35 km/h, while the operational range was 110 km and 60 km cross-country. The weight of this vehicle was 2.7 tonnes. The modified versions with the extra added weight likely had slightly worse overall driver performance.

Suspension

The T-27 was used in two similar suspension configurations. One used the original 4 road wheels placed on a suspension cradle. In addition, there was a front drive sprocket and rear idler. The road wheels were placed in par on bogies which were suspended using simple flat leaf springs. The Soviets were not satisfied with this design, so they improved it by adding another pair of wheels.

The first prototype armed with the 37 mm gun used a four-wheel suspension. While there is very little information on these vehicles’ overall construction, thanks to surviving photographs, it is possible to identify that some structural changes were made. Given the recoil force of the gun, the integral structure of the suspension had to be strong. The part of the suspension cradle that held the rear idler was reinforced. Lastly, the upper track guiding rod was replaced with two simple return rollers.

This arrangement appears to have been insufficient for this modified vehicle. So, on the second prototype, a six-wheel suspension was used. It also received extensive structural improvement to better cope with the gun’s recoil. Its suspension cradle appears to have been slightly larger than on a standard T-27 vehicle. While the two upper return rollers remained, they appear to have received some kind of leaf spring addition.

Superstructure

The superstructure is another part of the vehicle that was heavily modified. Originally, the T-27 had a simple box shape superstructure that covered most parts of the vehicle. The crew’s head (and the engine’s top) were protected by a pyramidal-shaped hatch. In front of the crew compartment, there was a hatch placed on the upper glacis that provided access to their transmission unit. The T-27 was built using simple plates connected using bolts.

The right part of the superstructure, where the machine gun port was originally located, was redesigned in order to fit the larger gun inside of it. This part was greatly extended forward to provide room for the gun mount. Not much is detailed in the sources about this new superstructure’s design. We can assume though, that due to the T-27’s small size, it would be quite cramped and difficult for the gunner to operate this gun.

Armament

The initial armament of the T-27 consisted of only one 7.62 mm DT machine gun. This proved to be completely inadequate and was the main reason why this project was initiated. Instead, the Soviet designers wanted to install a 37 mm gun. Two guns were initially considered: the PS-2 and the B-3. Due to delays in production, neither of them was available for use.

As a replacement, a 37 mm Hotchkiss which was in service by the Soviet Army was chosen instead. In the first prototype, this gun was placed in the enlarged gunner position. The overall construction and the general characteristic of this gun mounted on the modified T-27 are not specified in the sources. What is known is that the performance of this vehicle was poor. The chassis became overburdened with the added weight of the gun, ammunition, and extra armor. It was noted that the ammunition for the main gun took up too much space inside the vehicle. As a temporary solution, a trailer was to be used to transport additional ammunition.

The second prototype received more modifications in order to provide more working room for the gun. The Soviet engineers were a bit overambitious, as they added a machine gun to this vehicle. For this reason, the main gun was placed in a lower position. Above it, a Degtyaryov 7.62 mm DT machine gun was placed on a ball mount. The machine gun could be operated independently of the main gun. In theory, this would provide armament to deal with the enemy armor and infantry. Realistically, this arrangement proved too much for the small vehicle and cumbersome to use.

Crew

The crew consisted of only two: the commander/gunner and the driver. The driver’s position was on the left and the gunner was on the other side. This arrangement was not changed on the modified T-27. Interestingly, on the second prototype, the Soviets tested the use of dual controls, meaning that both crew members could drive should the need arise.

Armor

Given its slight weight and small size, the T-27 was only lightly protected. The armor thickness of the front armor was 9 mm, the side and rear were 8 mm thick, the bottom was 4 mm, and the top was 6 mm thick. There is no mention in the sources that the armor of the modified T-27 was changed. This level of protection ensured that the vehicle was protected against small arms fire and shell splinters, but little else.

Ultimate Fate

After a series of examinations, it quickly became obvious that this concept was flawed. The gun was simply too heavy for the chassis. The use of machine gun placed above the gun was difficult to operate. The added weight led to engine overheating problems. As a result, the project was rather quickly terminated. It is not clear if any additional vehicles were built beside the two already mentioned prototypes. Some sources, such as D. Nešić (Naoružanje Drugog Svetsko Rata-SSSR) mention that a small production run was made.

Despite the cancellation of this project, the experimenting with stronger armament on the T-27 continued. An installation of a recoilless gun on the right side of the vehicle was tested. In addition, a modified version with a 76.2 cm gun installed to the vehicle’s rear was also built. None of these entered productions and any further work on improving the armament of the T-27 was discontinued.

Conclusion

While the whole concept of rearming the older design with a stronger gun was sound, in reality, this was impossible to achieve. The T-27’s chassis was simply too small and weak. The 37 mm armed T-27 project was essentially doomed from the start. The gun weight and its recoil were probably too much for the small chassis. In addition, the working space inside it was quite limited to effectively operate this gun. This ultimately led to the cancellation of this project, but at least, it offered some experience to the Soviet tank engineers.

T-27 with the 37 mm gun Technical specification
Crew	Commander/Gunner, and Driver
Weight	over 2.7 tonnes
Dimensions	Length 2.65 m, Width 1.83 m, Height 1.47 m
Engine	44 hp Ford petrol engine
Speed	45 km/h
Primary Armament	37 mm gun
Secondary Armament	One 7.62 mm DT machine gun (second prototype)
Armor	6 to 9 mm

Source

S. J. Zaloga and J. Grandsen (1984) Soviet Tanks and Combat Vehicle of World War Two, Lionel Leventhal
T. Bean and W. Fowler (2002) Russian Tanks Of World War II MBI Publishing Company
Svirin M. N. (2008) Самоходки Сталина. История советской САУ 1919-1945, Эксмо
A.G. Solyankin (2002) Отечественные бронированные машины. XX век Том 1, Цейхгауз
D. Nešić, (2008), Naoružanje Drugog Svetsko Rata-SSSR, Beograd
http://battlefield.ru/content/view/72/50/lang,en/
https://www.armedconflicts.com/T-27-t6527

Soviet Union (1935)
Self-Propelled Gun – 1 Prototype Built

Prior to the Second World War, the Soviets were experimenting and developing a series of projects intended to improve the performance of already existing armored vehicles. One of these projects was an attempt to resolve the issues with the weak armament of Soviet amphibious tanks. This would lead to the creation of the experimental SU-45. While one prototype would be built, its poor performance would eventually lead to the cancelation of this project.

The SU-37 project

The Soviet Scientific and Technical Department Agency of Automobiles and Tanks (which was part of the Ministry of Defense of Red Army) issued a request to the director of plant №37 to begin designing and building a new self-propelled vehicle based on the T-37A amphibious light tank. The timeline was quite short. The order was given on 22nd March and the first prototype was to be completed by 11th April the same year. In reality, this task could not be achieved effectively in such a short period of time.

The T-37A was an amphibious light tank developed during the early 1930s in the Soviet Union. It was lightly protected and armed with only a single machine gun. The crew consisted of the driver and the commander/machine gunner. The T-37A was primarily intended to perform reconnaissance operations. Over 2,000 vehicles would be built, with most being lost during Operation Barbarossa in 1941.

When the tactical and technical requirements arrived, they included an option to use either an unchanged T-37A chassis or to build a completely new chassis with some elements taken from this vehicle. Other requirements included a maximum weight of the vehicle of 3 tonnes. The armament would include one 45 mm gun with a traverse of 30° (in both directions) and elevation of -8° to +25° and a DP machine gun. The ammunition load for the gun was to be 50 rounds, with an additional 1,000 for the machine gun. The overall armor protection had to be at least 5 mm thick (except the roof, which would be open-top) including an armored shield for the gun.

The new vehicle, which would receive the SU-37 (Samokhodnaya ustanovka – self-propelled) designation, was to have the same amphibious properties as the T-37A. It should have supplemented the weak firepower of the T-37A formations with its stronger armament. In addition, it was to fulfill a mobile anti-tank role on a regimental level.

The improved SU-45 replacement project 

Despite the short-term development goal, the actual design work on the new self-propelled vehicle dragged on. Almost from the start, a number of problems arose. One issue was the weight of the new vehicle was much larger than expected. This prevented it from being able to cross water obstacles. Another even greater problem was that many components for the T-37A were no longer being produced. A team of engineers under the leadership of I. Arharov was tasked with resolving the problems with the SU-37 and trying to find a better solution.

In November 1935, a mock-up version of the new modified self-propelled vehicle was presented to the Agency of Automobiles and Tanks of the Ministry of Defense. The basis for this new vehicle was the T-38 amphibious light tank. The T-38 was an improved version of the T-37A. It had a slightly modified suspension, overall simpler construction, better buoyancy properties, and the turret position was changed to the left side of the hull. The armament, crew configuration, and armor were the same. Over 1,200 of his vehicles would be built from 1936 to 1939.

This vehicle incorporated the chassis, transmission, and engine from the T-38. The main gun was still the same 45 mm anti-tank gun. The driver/gunner was initially positioned on the right side. The commission requested that the driver’s position be changed to the left side and that he no longer have to operate the gun. The first prototype was to be built by the start of 1936.

Name 

In the documents of the Agency of Automobiles and Tanks of the Ministry of Defense, the project received the “SU-45” designation. It is somewhat confusing that the Soviet Military Authorities decided to name the previous prototype based on the chassis on which it was based (SU-37 from T-37A) and the second prototype by the main gun caliber. This designation practice would continue on, many later developed self-propelled vehicles receiving names based on their gun caliber.

Author D. Nešić, (Naoružanje Drugog Svetsko Rata-SSSR) notes that the designation for this vehicle was T-45. This should not be confused with a Soviet attempt to improve the T-60 tank during the Second World War. If this is a mistake or misunderstanding on behalf of the author is difficult to know.

Specifications

Note that, due to the generally obscure history of this vehicle, sources greatly disagree about nearly all of the SU-45 components.

Chassis

For the construction of the SU-45, a modified chassis of a T-38 light amphibious tank was used. The front part of the chassis housed the crew and the main gun. To the rear, the engine and the transmission were placed.

Engine and transmission 

The SU-45 was powered by a four-cylinder liquid cooling 40-45 hp GAZ-A engine. The maximum speed of the SU-45 with this engine, on a good road, was 45 km/h. The off-road speed and operational range are unknown. The GAZ-A engine was started by using a MAF-4001 electrical starter. The position of the transmission was changed to the rear.

Suspension

With the increased number of crewmen, added ammunition, and other changes, the weight of the vehicle reached 4.5 tonnes (or 4.3 tonnes, depending on the source). The T-38 running gear had to be redesigned. This included adding an additional roadwheel (on both sides), making it five in total (from the original four on the T-38). While the added wheel was suspended individually, the remaining four were placed in pairs on a bogie suspension unit. All five wheels were rubber-tired. The idler and drive sprocket on the SU-45, in comparison to the T-38, had switched positions. The driver sprocket was now at the rear, while the idler was at the front. The two return rollers remained unchanged.

Superstructure

Not much is detailed in the sources about the superstructure’s design. The SU-45 was actually an open-topped vehicle. To shield the crew from the weather and elements, a canvas cover could be placed on top of the vehicle. Its overall construction, based on the few existing photographs, appears to have been simple in design. The SU-45’s side armor plates were flat, while the front plate was at an angle. The front, where the crew compartment was located, was slightly raised in comparison to the rear engine compartment. This was meant to provide the crew with protection but also to reduce the vehicle’s overall weight.

On the right front plate, a large square-shaped driver’s visor was placed. In its center, a smaller vision port was located. On the opposite side of it, a ball mount for the machine gun was located. Close to it, a pyramid-shaped cover can be seen. Its purpose is not clear, but it is likely to have been a protective cover for the gun’s sights.

Armament

The 45 mm M1932 anti-tank gun was chosen as the main armament of this vehicle. It was the standard Soviet infantry anti-tank gun prior to and during the first years of the war. While it would be replaced with larger caliber weapons, due to the large production numbers, it remained in use during the war. The 45 mm M1932’s armor penetration at 500 m (at 0 degrees) was 38 mm. The rate of fire was some 12 rounds per minute.

The main gun on the SU-45 was positioned in the front center of the vehicle. It was protected by a round shield placed in front of the gun. The elevation of the gun was -3° to +10°, while the traverse was 10° in both directions. The ammunition load consisted of (depending on the sources) between 50 to 100 rounds. The latter number seems to be unlikely, given the small size of the vehicle. The secondary armament consisted of one 7.62 mm DT machine gun. It was placed in a ball mount and positioned to the left side of the vehicle. It was operated by the vehicle’s commander. The ammunition load for this machine gun was around 1,100 rounds. The machine gun was also provided with a pivoting mount to be used as an anti-aircraft weapon.

The Crew

Depending on the source, this vehicle is listed to have either two or three crew members. In case it had three crew members, these included a commander/gunner, loader, and the driver. Despite initial plans to change the position of the driver to the left, on the prototype, he was seated on the right side. The remaining crew members were positioned opposite the driver. The commander was overburdened, as he had to operate the gun and the machine gun and command the vehicle, greatly reducing his effectiveness.

Armor protection 

The SU-45 was lightly protected, with armor plate thicknesses ranging from 6 mm on the sides to 9 mm on the front. These armor plates were connected using screws and rivets. This armor thickness was sufficient, at best, against small-caliber bullets.

Ultimate fate

Despite the plans to complete the first prototype by January 1st, 1936, due to many delays, it was only completed in the spring of that year. Once ready, a series of trails with the SU-45 were carried out. During these, a number of flaws in the design were noted. The T-38 chassis was overloaded and often led to mechanical breakdowns. The engine was underpowered, with an ineffective cooling system which often led to overheating. The transmission was also problematic and unreliable.

Seeing the results of these trials, the Agency of Automobiles and Tanks of the Ministry of Defense insisted that all these flaws and problems be resolved. The experiment would be carried on to the experimental T-38M chassis, but ultimately lead nowhere, and the whole SU-45 project was scrapped.

Conclusion

The SU-45 was intended as a lightweight self-propelled vehicle which was to provide additional support fire for the amphibious light tanks in cooperation with other units. The SU-45 design ultimately proved to be a failure. Having too great weight prevented it from being used as an amphibious vehicle. The engine had overheating problems. While it had much-improved firepower in comparison to the vehicle it was based on, it retained weak armor protection. This vehicle would never enter production and the Soviet units had to rely on their obsolete T-37 and T-38 vehicles. During the Second World War, these also proved to be unsatisfactory designs in many regards.

 

SU-45 specifications
Dimensions (L-w-h)	4.2 x 2.36 x 1.62 m
Weight	4.3 to 4.5  tonnes
Crew	3 (Commander/Gunner, Loader, and Drive)
Propulsion	40-45 HP GAZ-A engine
Speed (road)	45 km/h
Primary Armament	45 mm M1932
Secondary Armament	7.62 mm DT machine gun
Armor	6 to 9 mm
Total production	1

 

Source

• L. Ness (2012) World War II tanks,  Harper Collins Publisher
• D. Nešić, (2008), Naoružanje Drugog Svetsko Rata-SSSR, Beograd
• Svirin M. N. (2008) Самоходки Сталина. История советской САУ 1919-1945, Эксмо
• A.G. Solyankin (2002) Отечественные бронированные машины. XX век Том 1, Цейхгауз
• http://aviarmor.net/tww2/tanks/ussr/su-45.htm

 

Soviet Union (1944-1945)
Heavy Tank Destroyers – 5 Prototypes Built

Dedicated Beast Slayers

In mid-1944, the Red Army recognized that it might need tanks that could consistently and reliably destroy the Wehrmacht’s most well-armored tanks. The Red Army fielded few tanks that could destroy the King Tiger, Elefant, and Jagdtiger reliably from medium-long ranges. Although it is true that the ISU-122, ISU-122s, ISU-152, and IS-2 were capable of destroying German heavy tanks, their combat results were not consistent enough. As a result, starting in June of 1944, five “BM” (“High Power” – Russian: “высокой мощности”) guns were developed for the ISU chassis. The resulting vehicles were: Object 243 (ISU-122-1 with the 122mm BL-9 gun), Object 246 (ISU-152-1 with the 152mm BL-8 gun), Object 247 (ISU-152-2 with the 152mm BL-10 gun), Object 250 (ISU-130 with the 130mm S-26 gun), and Object 251 (ISU-122-3 with the 122mm S-26-1 gun). More gun projects were being developed at this time, but no others appeared to be mounted onto a chassis. The guns proved capable, on paper, of destroying tanks such as the Jagdtiger, but testing showed that they were simply not practical. Moreover, these projects took well over a year to refine, and seeing as though the war ended before they were complete, they were all dropped.

A table with comparative statistics is provided at the bottom of the article.

Context: Soviet guns against German armor

Mythbusting: The SU-152 and ISU-152 were “Beast Killers”
Soviet wartime propaganda suggested that the SU-152 and ISU-152 (SU being based on the KV chassis, ISU being based on the IS chassis) were “Beast-Killers” because they could destroy Panthers, Tigers, and Elefants. The ISU-152’s 152mm ML-20S howitzer was, indeed, capable of destroying heavy German armor, but this required a direct hit with a High Explosive (HE) shell. Such a direct hit could do one of three things to disable the tank: destroy the vehicle’s drive systems, kill its crew, or blow the turret / casemate / hull open (or even clean off, in the case of turrets). Armor Piercing (AP) and Concrete Piercing shells were developed, but these were expensive and complicated to make, hardly more effective than HE rounds, and thus were scarcely supplied – even at Kursk! However, the ISU-152 was not a dedicated tank destroyer – it was an assault gun designed for bunker busting and indirect fire. Needless to say, using an assault gun as a tank destroyer was risky business.
Firstly, the gun would need to be fired at short ranges against enemy tanks. This is because the ML-20S was a fairly low velocity howitzer, which would simply not be accurate enough to engage tanks from distances. Consider also that the vehicle had a maximum of 90 mm of armor, which meant that it whilst it was adequately protected from some German guns at long ranges, it simply was not thick enough to protect the vehicle in the short ranges it would need to operate in as a tank destroyer. For example, the 7.5 cm KwK 40 L/48, as mounted on StuGs, Panzer IVs, and Jagdpanzers, could penetrate 97 mm of armor at 500 m, and 87 mm of armor at 1000 m, at 30 degrees (the ISU-152 casemate was barely sloped at all). Also consider that the vehicle was simply not mobile enough to be engaging more nimble German tanks, and could probably be outmaneuvered anyway.
Yet another major issue of using the ISU-152 as a tank destroyer was that it could only manage 1-3 rounds per minute (depending if it had one or two loaders, and how experienced they were). This meant that in any type of ‘duel’, the ISU-152 would not only need to fire first, but also guarantee a hit, or practically any opposing German tank could get numerous shots off against it – as mentioned early, likely knock-out blows. Having said this, it did not seem to be a consideration taken into account when making the “BM” projects, as the guns all had equally as poor rates of fire.
In conclusion, the ISU-152 did not live up to its legendary name. Other Soviet field guns and tank destroyers had somewhat better results compared to the ISU-152, although the results were still not quite satisfactory.
Mythbusting: The 122 mm A-19S and D-25T / S were sufficient
It is a commonly held belief that the 122 mm D-25T / S and A-19S were sufficient at destroying the heaviest German armor. This belief is somewhat problematic, given the weight of the evidence.
According to a Wa Preuf 1 (a Wehrmacht weapons research facility) report from October 5th, 1944, the 122mm A-19 (the A-19S being used on the ISU-122, the latest Soviet SPG at that time) could not penetrate the upper glacis of a Panther. However, it could penetrate the lower glacis from a distance of up to 100 m, the mantlet from 500 m, and the side of the turret from 1500m. This was still somewhat wanting, as the Red Army would prefer to engage such tanks from longer ranges, to prevent heavy losses of their own tanks.
The improved 122mm D-25T (which was used on the IS-2, the D-25S was essentially the same, and was used on the ISU-122S) seems to have fared much better against German armor. Testing of the gun on the IS-2 platform in Kubinka in 1944 suggests that a King Tiger’s turret (likely the side) could be penetrated from up to 1000-1500m. The welds of front hull seams could also be penetrated from 500-600m. Whilst these penetration statistics might make the D-25T sound more promising, they must be taken with some caveats.
Firstly, to score such hits would require a very skilled and very experienced gunner – especially to score a hit on the turret from a range of up to 1500m. Secondly, similar to the ML-20S, the D-25T could only manage up to 3 rounds per minute. Thirdly, the validity of these statistics has been called into question, because they come from Soviet sources. In the past, these statistics were often exaggerated for propaganda purposes. Finally, the very fact that the ISU “BM” projects were put into production suggests that the Soviets knew that the D-25T would not give consistently reliable results in AT duties.
Whilst, indeed, the D-25T was, in theory, capable of destroying the heaviest German armor, it was perhaps not as reliable as it needed to be in the field. Of course, it is true that penetrations were not required to disable the tank or kill the crew (both in the case of the ML-20S and D-25T), but one could not simply rely on non-penetrating hits to, in some manner, disable the tank.
As a result of these relatively unsatisfactory Soviet AT capabilities against the Wehrmacht’s heaviest tanks, in June 1944, Zavod Nr. 100 began developing new, high velocity 122 mm, 130 mm, and 152 mm guns to be mounted on the ISU (and perhaps IS and KV) chassis.

Object 243 (ISU-122-1)

Object 243 (ISU-122-1) with the 122 mm BL-9. This vehicle is distinguishable as its gun has no muzzle brake, and looks like an elongated A-19S. However, the gun replicator has been angled (see the rectangular plate on the mantlet below the gun), unlike a regular ISU-122.

• The Object 243 featured the 122 mm BL-9 gun – one of the infamous BL guns made at OKB-172. The vehicle can be distinguished by its gun and mantlet. The gun essentially looked like a longer version of the A-19S. The mantlet also had some tweaking to fit the longer and heavier gun – most notably, the tip of the gun replicator has been angled to one side (just below the gun).
• It could penetrate 204 mm of armor at 1000 m, with 2 rounds per minute.
• The gun’s muzzle velocity was 950 m/s with an 11.9kg AP shell.
• It had a range of 10,700 m, compared to the 6000 m range of the 152 mm ML-20S of the ISU-152 and SU-152.
• It could carry 20 AP rounds, the same as the ISU-152.
• Like the other “BM” guns, the BL-9 was likely too powerful for its mountings, which caused mechanical issues.

Object 246 (ISU-152-1)

Object 246 (ISU-152-1) with the 152 mm BL-8. This vehicle is distinguishable by its slightly longer gun than the Object 247 (15 cm, or 5.9 inches), but the same muzzle brake, and its unchanged gun replicator.

• The Object 246 featured the 152 mm BL-8 gun. This vehicle can be distinguished by its distinctive muzzle brake, and unaltered gun replicator.
• It could reportedly penetrate 203 mm of armor at 90 degrees from up to 2000 m away (dubious) ¹, with 3 rounds per minute.
• The gun had a muzzle velocity of 850 m/s with a 43.56 kg HE shell.
• It had a maximum range of 18,500 m.
• It could carry 21 rounds.
• Whilst these results sound excellent, trials in December 1944 showed that the crew found operating the gun difficult, the muzzle brake and breech block were unreliable, and the barrel strength and angle of horizontal guidance were unsatisfactory. Consider also that the very long gun would limit the maneuverability of the vehicle, much like the D-25S on the ISU-122S limited its maneuverability. As a result, the 152mm BL-10 was developed…

Object 247 (ISU-152-2)

Object 247 (ISU-152-2) with the 152 mm BL-10. This vehicle is distinguishable by the length of its barrel (it was slightly shorter compared to the BL-8), its muzzle brake, and its altered gun replicator.

• The Object 247 fitted the 152 mm BL-10 gun, an improvement of the BL-8. This vehicle can be distinguished by its muzzle brake and slightly altered gun mantlet, whereby the rectangular tip of the gun replicating system had been angled, unlike the original ISU mantlet.
• It could penetrate 205 mm of armor from 1000 m.
• The gun had a muzzle velocity of 851 m/s with a 43.56 kg HE shell.
• It had a maximum range of 17,000 m.
• It could carry 20 HE shells.
• Testing revealed that barrel integrity and angle of horizontal guidance were poor.
• It was eventually deemed that there was no need for this work to continue, mostly because the war was over, and there was no need to combat heavily armored German vehicles.
• Consider also, that whilst the barrel length was a little shorter than the BL-8, it, too, would still suffer from maneuverability issues as a result.

Object 250 (ISU-130)

Object 250 (ISU-130) with the 130 mm S-26. This vehicle is distinguishable by its unique muzzle brake.

• The Object 250 (ISU-130) was built in autumn, 1944 and featured a 130 mm (5.12 in) S-26 gun. This gun is sometimes referred to as a naval gun, but this is not entirely accurate – the S-26 derived from a naval gun and featured a rectangular muzzle brake and horizontal wedges.
• It could penetrate 196 mm of armor from 1000 m.
• It had a muzzle velocity of 702 m/s, firing a 33.4kg HE shell, with 1.5-2.5 rounds per minute.
• It had a range of 15,000 m.
• It could carry 25 shells, which were smaller than 152mm shells, meaning that it provided similar ballistic results to the 152mm BM guns, but could carry more shells.
• In October 1944, the ISU-130 underwent factory trials, and the following month, trials were held at the Polygon.
• A major concern came from the caliber – 130mm. The issue was that the army would have to make special arrangements for the 130mm naval shells to be supplied to the army, and thus it was decided that a gun using current army-issue 122mm or 152mm would be preferable.
• Testing of the ISU-130 ended in 1945, and the gun was sent to the TaSKB for completion, but the war was over, and the project was disbanded.
• The ISU-130 is currently preserved at the Kubinka Tank Museum.

The ISU-130 preserved at Kubinka.

Object 251 (ISU-122-3)

Object 251 (ISU-122-3) with the 122 mm S-26-1. This vehicle is distinguishable by its round gun mantlet and its unique cylindrical muzzle brake.

• The Object 251 was derived from the ISU-130. It featured essentially a 122 mm version of the 130 mm S-26, which was designated the S-26-1. It had a round muzzle brake, different components, but the mantlet was the same shape.
• It could penetrate 204 mm of armor from 1000 m.
• It had very similar ballistics to the BL-9, but had a muzzle velocity of 1000 m/s, firing a 25kg shell.
• It could fire a disappointing 1.5-1.8 rounds per minute.
• It underwent field tests in November 1944, but according to sources, something (probably the mantlet and / or gun mechanism), was simply not strong enough to withstand firing the gun.
• The gun project was totally completed in June 1945, but was abandoned due to the war’s end.
• (Note that the ISU-122-2 was the ISU-122S with the 122 mm D-25S, hence the skip from ISU-122-1 to ISU-122-3).

Conclusion

The “ISU High Powered Gun Projects” were, in many respects, a failure. True, the guns were incredibly potent, particularly in the case of the S-26-1, which could penetrate 204 mm from 1000 m. They also had a very long range, only limited by the elevation of the ISU mantlet. However, they were simply not practical and mechanically reliable enough for their intended purpose, which was to knock out the thickest armored Wehrmacht tanks consistently, and from long ranges.
Even if the vehicles were put into serial production, how often these tanks would face off with the most heavily armored vehicles of the Wehrmacht is questionable. With Jagdtigers, King Tigers, and Ferdinands being so rare, the war was more likely to have ended before the ISU High Powered Projects saw combat with the vehicles they were designed to destroy. What had ultimately put the nail in the coffin for these guns was that the war had ended, and they were no longer necessary.

Sidenote: Designations and identification through photos

In the writing of this article, it has been exceptionally difficult to pin down which photos correspond to which project. Indeed, some sources only mention four (in some cases, only three) High Powered Gun Project vehicles. It has been the author’s conclusion that there were five such High Powered Gun Projects mounted onto ISU chassis, as outlined in Solyankin’s book “Советские тяжелые самоходные артиллерийские установки 1941-45″. Most online sources, particularly non-Russian language sources, are incredibly inaccurate. Gun statistics were mostly provided by a Soviet data set as provided by Tankarchives.blogspot. However, these statistics sometimes differ with Solyankin.

Notes:

¹ – Note 1 – Most data has been obtained from this Soviet data set. However, certain statistics have not been given and have been obtained from alternative (potentially dubious) sources. Where necessary, statistics provided by Solyankin have been used, but these are questionable.
² – Note 2 – Experienced crews were able to load much faster. Consider that the BM guns were likely tested by experts in test ground conditions, thus likely making their rounds per minute data higher than would be in the field, by more typical tank crews.
³ – Note 3 – Obtaining the ISU-122S’ ammo capacity has been difficult. It is reported that with a crew of four, instead of five (IE, one loader instead of two), then ammo capacity was increased, but the only given figure is 30, presumably with two loaders.
Sources:
“Germany’s Panther Tank: The Quest for Combat Supremacy”, by Thomas Jentz
“Sturmgeschutz & Its Variants”, by Walter J. Spielberger
“Советские тяжелые самоходные артиллерийские установки 1941-45”, by A.G. Solyankin
battlefield.ru
battlefield.ru (second page)
forum.axishistory.com
tankarchives.blogspot
tankarchives.blogspot (second page)
tankarchives.blogspot (third page)
armchairgeneral.com forums
WW2 AT Penetrations.pdf
alternatewars.com
alternatewars.com (second page)
ftr.wot-news.com
3.bp.blogspot

	BL-9	BL-8	BL-10	S-26	S-26-1	ML-20S	D-25S	12.8cm PaK 44 L/55
Chassis	Object 243	Object 246	Object 247	Object 250	Object 251	ISU-152, SU-152	ISU-122S	Jagdtiger
Caliber	122 mm	152 mm	152 mm	130 mm	122 mm	152 mm	122 mm	128 mm
[email protected] deg	204 mm from 1000 m 157 mm from 1500 m 155 mm from 2000 m	203 mm1 from 2000 m (Dubious)	205 mm from 1000 m 202 mm from 1500 m 160 mm from 2000 m	196 mm from 1000 m 184 mm from 1500 m 156 mm from 2000 m	204 mm from 1000 m 157 mm from 1500 m 156 mm from 2000 m	125 mm from 500 m	147 mm from 500 m 138 mm from 1000 m and 129 mm from 2000 m	200 mm from 1000 m 30 degree angle PzGr.43 shell
Rounds per Minute	2	3 1	No data 1	1.5-2.25	1.5-1.8	1-3 2 (crew dependent)	1-3 2,3 (crew dependent)	2
Muzzle velocity	950m/s1(AP) 700 m/s (HE)	850 m/s (presumably HE) 1	826 m/s (AP) 851 m/s (HE)	898 m/s (AP) 702 m/s (HE)	1000 m/s (AP and HE)	600 m/s (HE)	800 m/s (HE)	950 m/s (AP)
Range	10,700 m	18,500 m 1	17,000 m	15,000 m 1	15,000 m 1	6000 m	5000 m	24,410 m
Shell Weight and Type	11.9kg AP	43.56kg HE	43.56kg HE	33.4kg HE	25kg HE	43.56kg HE	25kg HE	28kg HE 28.3kg AP
Ammo Capacity	20	21 1	20	25	24	20 (ISU-152)	30 1, 3	38-40
Overall length, chassis included	11.15 m (36.58 ft)	11.82 m (38.78 ft)	11.67 m (38.29 ft)	11.42 m (37.47 ft)	11.26 m (36.94 ft)	9.18 m (30.12 ft)	9.85 m (32.32 ft)	10.65 m (34.94 ft)

Illustration of the Object 247/ISU-152-2 armed with the 152mm BL-10 gun by Tank Encyclopedia’s own David Bocquelet