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WW2 Soviet Prototypes

GAZ-68 / KSP-76

Soviet Union (1943-1944)
Experimental wheeled infantry support gun (1 built)

The SU-76 remains, to this day, one of the most well-known Soviet self-propelled guns of the Second World War. Yet, at the start of its production, it was plagued by unreliability and mechanical issues caused by its drivetrain. Thus, production was halted at only 560 units in order to remedy these problems. Solutions came with the SU-76M in 1943, but in between this period, another vehicle was designed, not to replace the SU-76, but rather supplement it. This was the GAZ-68 (also later referred to as KSP-76). Meant as a desperate and ultimately unsuccessful attempt to bolster tactical mobility, it was meant to provide close support artillery for rifle and cavalry units through direct fire. The GAZ-68 was based on a truck chassis, and the main gun would still be the famous ZiS-3 field gun.

SU-76M in what seems like Berlin, 1945. The SU-76M was an attempt to fix some problems with the SU-76. The GAZ-68 was a different vehicle in its role but would have functioned alongside the SU-76s.
Source: Pinterest

Why?

Throughout the early stages of the Second World War, the Soviet military found itself in a dire need of a fast vehicle, with good firepower, able to take on German Panzers but also other targets. Mainly, it would assist the infantry units in dealing with armored and unarmored targets, but also have the capability of responding quickly, moving and penetrating deep into enemy lines, accompanied by infantry attacks. Until 1943 and ‘44, the RKKA had no designated infantry support vehicle, relying entirely on towed artillery. Using a wheeled chassis as a basis, would allow much greater on-road speed, while also, theoretically, keeping production and maintenance costs down. On paper, a vehicle like the GAZ-68 was just what the Red Army needed, but in reality, it was the complete opposite, a consequence of the Soviet war and industrial struggle. Contrary to popular conceptions, this vehicle was not meant for artillery units for indirect fire or ‘shoot and scoot’ purposes, rather just an infantry support gun.

Front of the GAZ-68 as it is preserved at Kubinka, Moscow.
Source: A. Tarasov’s personal collection

Development

Shortly after the battle of Kursk (July – August 1943), where the use of mobile defenses and counter-attacks (plus numerical superiority) proved key for the Soviet victory, the mobility of artillery and self-propelled guns proved crucial. Thus, the Gorky Automobile Plant (Gorkovsky Avtomobilny Zavod, GAZ) started the development of a wheeled infantry support gun with the approval of the head of GAZ, V.A. Grachev, who was head designer of the project, while N. Astrov was head of the project. Already in August of 1943, the design office and plant management approved the idea. Grachev, a lesser-known name within western literature, was the chief designer at GAZ between 1941 and 1944 when he created many vehicles, most notably the GAZ-64 and BA-64. Post-war, he continued his career at ZiL, where he created, among others, the famous ZiL-157 and BTR-152.

The first ideas involved mounting a ZiS-3 gun on a 1½ tonne truck chassis, with only minor modifications. Clearly, the main goal here was to get a mobile vehicle for as little money as humanly possible.

Drawings for the installation of a ZiS-3 76 mm gun on a truck chassis, which has been stripped down to the bare minimum, missing even an enclosed driving cabin. For obvious reasons, the combat value of such a creation would be extremely limited.
Source: Солянкин А.Г., Павлов М.В., Павлов И.В., Желтов И.Т. Отечественные бронированные машины. XX век. Том 2. 1941-1945

The idea of a wheeled infantry support gun interested the Soviet military, leading to a go-ahead to the project from the People’s Commissariat (Ministry) of Medium Machine Building and the Main Armored Directorate of the Red Army (GABTU). Previously, all self-propelled artillery projects were under the command of GAU (Main Artillery Directorate), until all the SPGs were re-subordinated to GABTU as Stalin personally was outraged that the GAU adopted SU-12 (SU-76) in an unsatisfactory condition. Thus, the Directorate of the Self-Propelled Artillery of the GABTU was established on the 21st of May 1943.

Work started in October of 1943 under the name ‘Izdelie 68-SU’, but this was changed to GAZ-68. By December, a wooden mockup was already completed and documentation on the vehicle from GAZ was sent to the GABTU in mid-December. The GABTU approved the project for further development. On the 7th of February, 1944, the GABTU gave a green light for the production of a prototype. It was around this time that the name ‘KSP-76’ appeared, most likely a product from GABTU to remove the GAZ factory name. It stands for Wheeled Self-Propelled Gun with a 76 mm gun (‘Kolyosnaya Samokhodnaya Pushka’, KSP).

An experimental model of the wheeled self-propelled gun KPS-76.
Curiously that the name in the document is КПС-76 (KPS-76), not KSP-76.
Source: TsAMO

Following the approval for a prototype, the design bureau quickly sent the plans and documents to the workshops, which meant that, by April, the armored hull was completed. This was designed by Y. N. Sorochkin and A. N. Kirilov and was to protect from small arms fire and splinters. To keep weight down, the top was left open. On the 4th of May, the prototype was already completed.

An important part of this quick development and production process was the use of an already tried and tested chassis (not that this meant much for the Soviets, as there were plenty of prototypes in all fields made pre-war, but in this case, it did help boost development). The GAZ-68 was based on the GAZ-63 truck, however, it needs to be pointed out that the production of the GAZ-63 began only in 1948. Rather, the GAZ-68 was based on the experimental GAZ-63 developed in 1939. Essentially this was an all-wheel-drive GAZ-51, which itself was made to replace the aging GAZ-MM. Ironically, a GAZ-MM superstructure was used for the prototype. A Dodge D5 Diesel engine was used, outputting 76 horsepower, coupled to a 4-speed transmission. These trucks were tested at Kubinka in 1940, with good results. Mass production was to begin in 1942, but the start of the Great Patriotic War (as WW2 is called in Russia) meant that all projects were canceled.

The GAZ-63 model 1939. Not to be confused with the GAZ-63 model 1948.
Source: Rus-texnika.ru

Grachev, very sensibly so, claimed that using this already finished and tested chassis would greatly increase the development speed and trials. The advantages of a wheeled vehicle over a tracked one are also clear, with cheaper maintenance and higher speeds on roads. The designers wanted to use as many readily available components as possible for reliability and production purposes. This idea was, however, the one that led to the GAZ-68’s demise.

Design

The GAZ-68 was surely an unorthodox vehicle, especially by Soviet standards. However, at its core, it was essentially a SU-76 on wheels, albeit 69 cm narrower, 65 cm lower, and 135 cm longer.

The superstructure was thinly armored, made from a simple box, and no roof. The gun was mounted slightly behind the front wheel axle. The driver was located to the right of the gun, and with the gunner to the left. Ammunition was stowed to the sides of the casemate and behind. Thanks to the long wheelbase, the vehicle was very low to the ground, ideal for ambushes and camouflage, but also offered good stability. The engine was located at the back, over the rear axles. The design was rudimentary and simple, allowing for a very cheap vehicle to manufacture if the situation of Soviet truck plants was not as disastrous as it was. The top could be covered with a tarpaulin to protect from precipitation and wind. Two large fenders would protect the front wheels. As a result of the lack of resources, automotive plants were forced to take shortcuts during production, such as fitting just a single headlamp. On the GAZ-68 it was placed on the left side fender, to not further impair the view of the driver. Coupled with the low-mounted gun, these give the GAZ-68 its iconic look.

The very low profile of the GAZ-68/KSP-76 can be seen here. It was only 155 cm tall, 54 cm shorter than the SU-76. This would have made it a smaller target, crucial for a vehicle with such little armor.
Source: Maximonline.ru

Crew

The vehicle had a crew of only 3, a gunner (who also served as a commander and radio operator), a driver, and a loader. The gunner was responsible for aiming and firing the main gun. He had two vision slits through which he could see, plus the scope of the ZiS-3 gun, extending above the frontal shield. If in doubt, he could just stick his head up to get a clear 360° view using a pair of binoculars. The gunner also had a panoramic sight at his disposal.

Overloading the gunner/commander with so many tasks is unusual for the Soviets, especially in a late 1943 design and it is noteworthy that there was also enough space in the vehicle to put a fourth crew member, although test reports claim other crew positions were cramped. It is also worth mentioning that the Soviets had already suffered catastrophic losses, especially in specialized troops, such as tankmen. This might have been a deciding factor.

Commander/Gunner’s location. Radio and equipment have been removed, but the sight is still there.
Source: svsm.org

As mentioned previously, the driver sat on the right. He had a slightly larger viewport to view out of compared to that of the commander. Oddly, the large steering wheel went above the viewport, which could have been inconvenient for taller drivers.

Driver’s position. Most of the electronics and dials have been removed, but there probably were not many to begin with. Note the large viewport.
Source: svsm.org

The loader was seated behind the gunner, on a foldable seat. He had a ready rack behind him, incorporated into the engine compartment and in front of the fuel tank, which was not very safe, but considering the overall protection, or lack thereof, it did not matter. Forty-one rounds were stored here, in a horizontal position. 13 more rounds were stored on the other side, vertically, behind the driver. The crew also had 2 PPSh submachine guns for self-defense, with 12 magazines (852 rounds).

View from the front of the rear of the fighting compartment. Note the foldable loader’s chair on the right. The rack is right behind him, but is, in this picture, almost obscured by the cover. On the left, the other rack can be seen, and other storage spots.
Source: svsm.org

Armament

The armament of the GAZ-68 was the trusty 76 mm M1942 ZiS-3 divisional gun, one of the most common guns within the Red Army at the time, and also the main weapon of the SU-76. The field gun was capable of both direct and indirect fire (once mounted on the GAZ-68 it was not). Over 100,000 units were produced by the end of the war and saw service post-war with many nations. It had a range of above 10 km and could use a variety of shells.

The KSP-76 would have most likely used AP and HE shells, but there were AP, APHE, HE, HEAT, Fragmentation, and other shells available. Most shells weighed around 6 kg and had a muzzle velocity between 680 and 700 m/s. On the KSP-76, 54 rounds were stored in total. The position of the gun in such a low profile vehicle affected its ergonomics compared to a regular field gun mount. The gun could only be elevated to +15° and depressed to -3° and had a horizontal traverse of 37°, 18.5° to both left and right sides of the gun.

The gun was supported by a travel lock mounted on the edge of the frontal slope. Despite the rather large compartment, the estimated rate of fire was 8 rounds per minute (one round in 7.5 seconds). The ergonomically well-placed ammo rack could have allowed an experienced loader to shorten the reload time even more.

The vehicle lacked any secondary armament, which was a common defect in Soviet SPGs, making them extremely vulnerable in close range combat with infantry, exactly the type of engagements the KSP-76 was meant to tackle.

View of the vertical breech and aiming system to the left.
Source: svsm.org
The iconic recoil system of the ZiS-3 mounted on the KSP-76.
Source: svsm.org

Armor

The armor of the vehicle was thin, only being able to withstand rifle fire and shrapnel. The GAZ-68 was never meant to be well armored in order to keep costs and weight down, plus its low silhouette would have played a big role in improving its survivability. The frontal plate was initially 10 mm thick, later increased to 16 mm. The top of the sides was 7 mm and the inwards angled bottom side plates 4 mm. This was not even bulletproof but would provide some protection against shell splinters and ricochets. The roof of the engine compartment was 5 mm thick but there was no protection over the heads of the crew apart from their own helmets leaving them, and some of the ammunition dangerously exposed. The cutting of corners and economy made in this aspect of the vehicle made it have a low unit production cost but would have clearly made it vulnerable to even rifle rounds from the side. The tires were bulletproof, filled with an elastic substance.

External view of the front corner, driver’s side. Note the thinness of the welded front and side plates. There were small covers for the viewports, but these seem to have vanished.
Source: svsm.org

Engine and Chassis

The chassis was, as previously stated, that of the GAZ-63 model 1939 truck. The engine and transmission were changed from the truck to a single GAZ-202 (some sources state that the engine was a GAZ-202, but the TsAMO document states that it was a GAZ-203), engine outputting 85 hp, mounted in the rear compartment, offset by 276 mm to the right. To the left of the gun, a 140 liter insulated fuel tank was placed. In front of this, the 41 round ammo rack was placed. A very scary thought, considering the armor was only a few millimeters thick! An upwards-facing cooling grille was placed in the back. The transmission was a 5-speed manual (4 forwards, 1 reverse) coupled to both axles. However, the rear axles could be disconnected from the drive when not needed such as on a long road march. The suspension was standard and common to the truck consisted of simple leaf springs and shock absorbers.

Rear top view of the prototype. The rear compartment housed the engine, transmission, fuel tank, and ammunition, with only 4-7 millimeters of protection.
Source: Topwar.ru

Trials and Fate

As soon as the prototype was finished, it began factory testing around May 1944 and had finished tests by autumn of the same year. From the Gorky factory, the GAZ-68 went to the Kubinka test range. Allegedly, it traveled under its own power and with an impressive speed of 60 km/h. Again, this information has to be taken with a grain of salt.

In September-December 1944 the experimental SPG was tested at Kubinka proving grounds and Gorokhovetskii artillery range. During a 2,528 km test drive, it is claimed to have reached a top speed of 77 km/h on-road, but this seems hardly possible in regular conditions. Even if it was true, the limited view of the driver would make such a speed hazardous, to say the least. The vehicle only had an 85 horsepower engine and weighed 5,430 kg battle-ready. During firing trials, 409 shots were fired of unspecified type at the Gorokhovetskii artillery range.

However, testing was not all going to plan for the Soviets. The original chassis took a hard beating and broke down frequently, putting into question the validity of the tests made at Kubinka of the GAZ-63. The driveshafts, gearbox, leaf springs, and frontal axle suffered some form of damage. To be fair, the GAZ-68 did weigh over 2 tonnes more, with different weight distribution. It was also noted that the crew compartment was too small and uncomfortable for some of the crew, especially the driver, who was cramped up by the gun and steering wheel.

The small silhouette and profile of the vehicle were deemed as a plus. However, there were significant issues with accuracy, thanks to the chassis and the suspension, which made the ride very bouncy. This also caused the sight and barrel to become misaligned after driving. Off-road tests were a mixed bag. On one hand, the GAZ-68 proved satisfactory, on the other, it was far inferior to what a tracked vehicle was capable of. Testing was finished by the 24th of December. The Military Council of the Armored and Mechanized forces of the Red Army (Военный Совет БТ и МВ КА, Voennii Sovet Bronetankovyh i Mekhanizirovannyh Voisk Krasnoi Armii), proposed to GOKO (State Committee on Defence) to produce the initial test batch of 10 units at the GAZ factory and undergo army tests. However, this was not achieved and, instead, the project was terminated altogether.

The situation of the war in mid-1944 was very different than that of a year earlier. The Red Army had been on the offensive for almost a year, pushing the Axis almost back to the pre-war borders, and the Allies had just landed in Normandy, sealing the fate of the war. The implementation of the GAZ-68 made even less sense now than it did before, and the questionable combat value it would have brought would far outweigh the industrial strain, despite the seemingly cheap production price.

Doomed from the start

Even before starting prototype production, the fate of the GAZ-68 was predetermined. The straightforward fact that it was based on a truck chassis, which for the designers certainly seemed like an advantage, but the industrial capabilities and resources of the USSR could not deliver. The Soviet industry could not keep up production of ZiS-5 and GAZ-AA simple flatbed trucks, even with help through the Lend-Lease program, let alone the mass-production of an even more complicated truck designed in 1939 and canceled because of the German invasion.

Automotive factories could not start assembly of a new, complex, and relatively new design, in the conditions that they could not even keep up with simple production models. It is important to note, both of these truck models were standard commercial trucks, with little to no improvements for off-roading or any sort of military specialization. Before the war, the Red Army only had the GAZ-M1 and no off-road trucks.

Side view of the prototype showing off the impressively low profile to a good extent. Note the tarpaulin and muzzle cleaning rod.
Source: Topwar.ru

The GAZ-68/KSP-76 was also doomed through its design. The use of wheels would have given it faster speeds on good terrain, but most of the western Russian terrain was flat plains and forest, with poor road connections. This is not to take into account the harsh conditions of thick winter snow or deep muds, where even tracked vehicles could struggle. The supply of tires before and during the war was also a big issue for the Red Army. While the situation to some extent improved during the war, they still relied on imported tires for around 33% of their needs.

In modern eyes, a wheeled vehicle might seem superior, as we now have many roads and good infrastructure, plus more advanced technologies, but this was Russia in 1943. The GAZ-68 was simply not compatible with Soviet military doctrine, industrial capabilities, and the terrain of Eastern Europe.

Compared to the SU-76, the GAZ-68 was far cheaper to build and maintain, was 54 cm lower, but with similar protection levels and firepower, in addition to the pros and cons of a wheeled chassis. Whether the KSP-76 was an improvement over the SU-76 is up to debate, but it clearly was not enough to justify the changing of truck production lines to a new vehicle this late into the war.

GAZ-68/KSP-76 illustrated by Pavel Alexe, funded through our Patreon Campaign

GAZ-68 / KSP-76 specifications (Source: TsAMO)
Dimensions (L-W-H) mm 6,350 / 2,050 / 1,550
Total Weight, Battle Ready 5.39 tonnes
Crew 3 (Commander, Driver and loader)
Propulsion X
Speed X km/h
Range X km
Armament 76 mm gun ZiS-3 M1942 Regimental gun (662 m/s muzzle velocity)
Ammunition count 54
Maximum speed, km/h 62.5
Average speed on a paved road, km/h 49.3
Average speed on an unpaved road, km/h 21.2
Engine GAZ-203 (with an aluminum head) outputting 85 hp
Fuel type and range KB-70 or B-70 fuel,
140 liters for 430 km range
Armor (frontal hull, fighting compartment), 7-16 mm
(Sides, rear hull and fighting compartment), 4-7 mm
Total Production 1 prototype

Sources:

https://topwar.ru/51030-kolesnaya-sau-gaz-68-ksp-76.html
S. Lopovok, Inventor and Rationalizer, No 12,
Zaloga, Steven J., James Grandsen Soviet Tanks and Combat Vehicles of World War Two
https://rus-texnika.ru/gaz-62-obrazca-1939-goda.html
A.V. Karpenko. Part 1. Light self-propelled artillery installations  Domestic self-propelled artillery and anti-aircraft installations
https://rus-texnika.ru/gaz-63-obrazca-1939-goda.html
https://tech.wikireading.ru/9308
Солянкин А.Г., Павлов М.В., Павлов И.В., Желтов И.Т. Отечественные бронированные машины. XX век. Том 2. 1941-1945
TsAMO & GABTU archives (from A. Tarasov)

Categories
Cold War Soviet Prototypes WW2 Soviet Prototypes

Object 704

USSR (1945)
Heavy Self-Propelled gun – 1 prototype built

The SU-152 and ISU-152 were, and still are, well known for their massive guns and impressive claimed capabilities against German tanks such as the Tiger and Panther. That is how they got their nickname “Zveroboy”, meaning beast killer. However, that was more related to propaganda than their actual usefulness as tank destroyers. Their massive 152 mm guns, while very effective if they hit the target, were rather inaccurate at long range, slow to aim and to reload, and limited in traverse by their mounting in a superstructure. These guns were not well suited for a tank destroyer. The SU-152 and ISU-152 were not, in fact, tank destroyers, but assault guns, meant to help Soviet attacks break down enemy defenses and strongpoints. Yet, for assault guns, their protection was more often than not, quite lacking. With the start of production of the Kirovets-1 (Object 703, or better known as IS-3), the opportunity arose to improve the “Beast Killers”, now focusing on protection. This vehicle was to become the Object 704 or Kirovets-2. It is also called ISU-152 model 1945 in Russian literature, however, it is likely that the Object 704 was never referred to as such in the short life it had, and could be a modern name, possibly invented at Kubinka, according to Russian historian Yuri Pasholok.

Despite the success of the ISU-152, its weak armor, tall silhouette, and inconvenient muzzle blast made the Soviets seek a replacement. Ironically, they never got one and the ISU-152 served decades after WWII. Source: Pinterest

Development

Due to the problems of the ISU-152, proposals came as early as 1944 from GABTU (Main Directorate of Armed forces) to the SKB-2 plant to upgrade the vehicle, however, little materialized. Then, work started on a new IS tank- the Kirovets 1 (IS-3).

There were also plans to modernize the gun on the ISU-152 as well. In 1943, the GABTU Artillery section stated that the 152.4 mm ML-20S howitzer was not suited for use on a self-propelled gun. The issues on the ML-20 naturally reflected on the battle performance of the ISU-152. An example was the TsAKB slotted muzzle brake kicking up a lot of dust, almost blinding the gunner after firing, and more importantly, revealing the vehicle’s position.

Thus, the GABTU put out a series of requirements for the modernization of the weapon. Firstly, this included the removal of the muzzle brake, changes to the breech, and improvements to the recoil system. OKB-172 was assigned to develop the upgrade by the 13th of January, 1944, headed by M. Tsirulnikov. The new gun was to be named ML-20SM, M standing for modernized. Blueprints were ready by the 1st of March of the same year and, by the 10th of March, the prototype was built in Factory No.172. The very next day, firing trials were undertaken, but after the 33rd shot, testing was halted due to poor operation of the new breech. Further tests were made through March until the 14th of April when it passed the test for rapid consecutive firing of 60 shots, which it fired in 39 minutes. While that might seem like a lot, the initial firing time estimation for them was 60 minutes (1 round per minute), the gun averaging 1.5 rounds per minute. Testing continued into May, the gun firing a total of 249 rounds, out of which 196 were with high explosive charges (for direct firing). The average rate of fire over the entire testing period was an impressive 2.9 rounds per minute. Factory testing of this gun continued until September 1944. Due to the high rate of fire and no muzzle brake, it was decided on the 2nd of October to mount the gun inside an ISU-152. Consequently, the gun was shipped off to Chelyabinsk, but, when it arrived in the middle of October 1944, it was unfinished! At the end of 1944, the GABTU stated that the gun needed urgent work and that factory No.172 workers should be sent to ChKZ. This only happened by mid-February 1945, when the battlefield was different and the IS-3 was approaching mass production, making the ISU-152 chassis archaic.

The massive muzzle blast made concealing the vehicle virtually impossible after firing. It also blinded the crew, so following the shot and keeping track of the target was a challenge. Source: Weapons of Victory

In fact, ChKZ had started working on an SPG based on the Kirovets-1 at the beginning of 1945. It received the name Kirovets-2. The chief engineer and designer was L.S. Trojanov.

A letter from Engineer-Lieutenant Colonel Markin, a representative of the GABTU in ChKZ, was sent to GABTU chief Engineer-Lieutenant Colonel Blagonravov on this topic. It stated that the Kirov factory (SKB-2 to be precise) was working on a Kirovets-1 based SPG, stating its armor thickness level and other features, namely that it used the same transmission, running gear and engine as the Kirovets-1. Most interesting is that, according to the letter, work on the prototype started on the 1st of February, 1945. The letter was sent 10th of February, 1945.

The Kirovets-2, later named Object 704, was an attempt to fix the main issues with the ISU-152, yet created more problems and was plagued by bureaucratic wrangling. Source: Topwar.ru

ChKZ also announced S.P. Gurenko, chief designer of Factory No. 172, saying that SKB-2 was working on such a vehicle. This led to engineers from No. 172 coming over to Chelyabinsk between the 14th and 20th of February. During this time, SKB-2 had sent the blueprints of the Kirovets-2 over to Factory No. 200 as well. Also in mid-February, the hull of the SPG was ready in ChKZ.

On the 3rd of March, a meeting was held on the topic of improving the Kirovets-2. The main issue brought up was fitting the ML-20SM, originally built for the ISU-152, into the Kirovets-2. The gun had been sitting for quite a few months in a hall somewhere in ChKZ. Other points discussed were further increasing the armor and thickening it from 100 to 150 mm (3.9 – 5.9 inches) and replacing the panoramic sight with a Hertz sight from a 76 mm Mod. 1943 ZiS-3 gun, as it was smaller. The telescopic sight was also changed for a smaller TSh-17. The traverse mechanism was altered and, most importantly, it was decided to give the Kirovets-2 a co-axial DShK heavy machine gun, mounted on the right side of the main gun.

The hull of the Kirovets-2 was ready in spring, but the gun was not mounted until halfway through June 1945. This delay was caused by bureaucratic disputes regarding the serial production of the ML-20SM gun. The tank became the Object 704, yet the Kirovets-2 name stuck with factory workers.

Layout and Design

The design of the Kirovets-2 was unique, having little resemblance to previous Soviet heavy SPGs. It still had a frontal mounted casemate, where the turret and pike nose of the IS-3 used to be. Due to the aim to improve the armor protection to the same level as the IS-3, the armor plates were thickened and angled throughout the casemate. On the ISU-152, the gun mantlet was a large frontal weak spot, yet on the Object 704, it was the thickest part of the tank. Interesting to add is that the bottom of the side casemate angled inwards a lot more than it appears to. The almost flat triangle shape part of the side superstructure is actually just a thin sheet of metal.

Although the IS-3 chassis was used, there were still some changes made. Namely, the engine plate was different and the exhaust pipe layout was the same as on the Object 701. It is unclear if this was done to save pieces for the production of the IS-3 or it was intentionally designed as such. An additional small construction detail is the use of several track types, satisfactory for a prototype built in a short period of time. There were 86 tracks per side, each track was 650 mm wide and they were connected by a single pin. The engine was the same V-2-IS engine, producing 520 hp, and the running gear and transmission were kept the same. The transmission was a multi-disc dry friction clutch. The gearbox was a 4+1 dual stage (high/low) manual, for a total of 8 gears forwards and 2 in reverse. The brakes were still planetary rotation mechanisms.

The hull is often said to be identical to that of the IS-3, but the exhausts and engine plate design are different. Note the thinness of the triangular-shaped side plates on the hull can be discerned here. Source: Yuri Pasholok

Despite the external differences, inside, the Object 704 was very similar to the ISU-152. It still had a crew of five; driver, gunner, commander, loader, and breech operator. The heavily angled sidewalls caused major internal ergonomic problems, namely storage for the huge two-part ammunition, which weighed 48.78 kg (107 lb) for the AP and 43.56 kg (96 lb) for the HE, no easy task to load in a tight space. Sacrificing crew comfort and ergonomics for protection was quite common in the late war and post-war Soviet tank doctrine.

Object-704 during testing. The extreme angles of the fighting compartment can be seen. Source: Pinterest

The vehicle’s silhouette was much shorter than that of the ISU-152, now being only 2,240 mm (88 inches) tall, but kept the same width.

Main Armament

The modernized ML-20SM lacked a muzzle brake, which improved the visibility and kicked-up less dust after firing. However, the recoil grew considerably, namely by 900 mm, so a recoil brake was added. The gun had +18° of gun elevation and a shockingly poor -1.45° of depression. The horizontal traverse was not much better at a very limited total of just 11° (5.5° on each side). The new gun fired the same two-part HE weighing 43.56 kg (96 lb) and AP ammunition, weighing 48.78 kg (107 lb), and had very similar ballistics to the standard ML-20S. The HE rounds had a muzzle velocity of 655 m/s, while the AP had 600 m/s. The gun could hit a 2.5 to 3-meter tall target reliably from 800 to 1,000 meters (874 to 1,093 yards), but had a direct fire range of 3.8 km (2.36 miles) and an indirect fire range was 13 km (8 miles).

When conducting indirect firing, the Hertz panoramic scope was taken out through the gunner’s hatch. The practical rate of fire is contradicting and ranges from one to a bit under three rounds a minute. A quick reload was not necessary for such a self-propelled gun, especially considering the terrible ammunition count inside the Kirovets-2; just 20 (19 according to the trial report, although the extra round could be loaded to be 19 +1)) rounds. These were placed on both sidewalls of the fighting compartment, and the charges were placed on the right wall and underneath the breech.

View of the breech of the ML-20SM. Note part of the loader’s tray to the bottom left and the coaxial DShK machine gun to the right of the gun. The manual traverse can also be seen, which was to be operated by the breech operator. Source: Yuri Pasholok

Secondary Armament

The vehicle was equipped with two 12.7 mm DShK heavy machine guns, one coaxially mounted and one on the roof, with 300 spare rounds of ammunition inside (600 according to Kubinka). There was a chute for the ammunition belt to slide over the main gun and into the machine gun.

The roof-mounted DShK was for anti-aircraft use and was mounted on a rotating ring over the loader’s hatch. The ring could swivel over and next to the hatch. The machine gun itself could also pivot on its mount. A collimating K-10T sight was mounted on the gun for easier aiming against aircraft.

For the defense of the 5 crew members, they were equipped with PPSh or PPS submachine guns. Some F-1 grenades could also be mounted on the sidewall, between the commander and breech operator.

Crew

The Object 704 had a crew of 5; driver, commander, gunner, loader, and breech operator. They would communicate with each other with a TPU-4F intercom, having a headset and a microphone. This was essential, as the crew sat quite far away from each other and communication was key in coordinating aiming and directions. Every crew member had his own entry and exit hatch on the roof of the vehicle.

The driver was located higher up in the hull than in the ISU-152, by 600 to 700 mm. Consequently, he did not have his own hatch in the front plate, instead, his vision relied on the single movable MK-4 periscope in his hatch, on the roof. As could be anticipated by such an arrangement, this was not enough, giving the driver rather poor vision when buttoned up. He was, however, also able to open the hatch (by sliding it to the side) and stick his head out in non-lethal environments. To control the tank, he had two mechanical tillers. To his right was the gearshift and the shift for the high/low gear ranges. On a good note, the driver no longer sat next to a large fuel tank, like on the ISU-152, which was good for morale.

The gunner sat behind and to the right of the driver, on a seat attached directly to the gun. There, he had the elevation control hand crank, as well as the trigger, his Hertz panoramic sight, and the 2.5x (other sources claim 4x) magnification TSh-17 sights. This sight was adequate for firing up to 1500 meters (0.93 miles). As previously mentioned, for indirect firing, the gunner’s hatch had to be opened and the sight raised through it. Both sights were illuminated for conducting nocturnal firing. Directly under the breech block was a floor-mounted escape hatch, for a total of six hatches.

The commander was on the opposite side of the driver, also having just one MK-4 periscope for external vision. He was responsible for the radio, placed right in front of him, on the frontal armor plate. This radio was a 10PK-26 radio, connected to the 24 volts onboard power transmitter. The frequency was 3.75 Mhz to 6 Mhz, with a wavelength varying between 50 to 80 meters. While stationary, the range was between 20 to 25 km, and it decreased slightly while on the move. The radio also allowed for communication on two fixed frequencies, simultaneously. The coaxial machine gun was also his responsibility, most likely having to fire it as well. Yet the traverse of the main gun was controlled by the breech operator and elevation by the gunner, so aiming would have been a coordination challenge.

Handling the massive shells was done by the loader. The shells were stacked on the side walls. He was also assigned operation of the anti-air DShK on top of his hatch. To aid him in loading, he had a loading tray, attached to the gun. A round would be rested on it until it was ready to load again. This meant that the loader did not have to hold the round until the breech was open again, a little but crucial detail considering the round’s weight. There were 12 rounds on the wall next to him, while the other 7 were on the other side, by the breech operator, and were a challenge to extract.

Perhaps the most curious crew member position is the breech operator. It is important to note that the breech design was quite ancient and could not open automatically. The breech operator would open the breech while the loader was manhandling the rounds into the gun. Then he would close it. He could assist the loader with charge amounts as well. This was done to decrease the strain on the loader, as it was no easy feat.

While testing reports were quite satisfied with the positions of the crew, a few issues were brought up. The angled sidewalls made storage of ammunition complex and accessing them was cumbersome. Let alone moving them out and into the gun, considering their weight. The elevation of the driver’s position also brought drawbacks, namely, he would bounce around when the tank was moving on poor terrain. This was strenuous on the driver. To boost morale and improve living conditions, two fans were placed behind the gun, to ventilate and remove toxic fumes, as well as a couple of dome lights.

Engine

As aforementioned, the engine was a V-2-IS outputting 520 horsepower. An ST-700 electrical motor, outputting 15 hp (11 kW), was used for starting the main engine. In cold winters, two compressed air cylinders were used to start the engine. These were located by the driver’s feet. An NK-1 diesel fuel pump was used, with an RNA-1 regulator and carburetor. Air filtering was done by a multicyclone air filter. There was also a heater, used to heat the engine in cold winters, but also the fighting compartment. A total of three fuel tanks were in the vehicle, two in the fighting compartment and one in the engine bay, for a total of 540 liters (143 gallons). Two (90 liters each) external fuel tanks were on the engine deck. These were not connected to the fuel system and were meant to be dismounted when entering battle. The engine allowed the tank to reach a top speed of 37 to 40 km/h (23 to 25 mph). The fuel range was around 180 km (112 miles).

The rear of the Object 704, where differences in the engine plate compared to the IS-3 can be seen, such as the tow hook placement. Source: Warspot

Armor

Protection was one of the main focuses of the Object 704 project. All armored plates were welded with heavy sloping all around the casemate. The front plate was 120 mm thick, angled at 50°. The lower plate was 100 mm (or 120, sources are conflicting or might imply there might have been different thicknesses proposed) angled at -55°. The mantlet had two layers of rounded 100 mm cast armor. The side was 90 mm angled at 15° from the side. Even the rear casemate armor was 80 mm at 21°. The tank was immune from the front to the 88 mm PaK 43 L/71 gun of the Tiger II, which it never got to fight. Despite this thick armor, the vehicle still had an acceptable weight of 47.3 tonnes (52 US tons).

This was a very well protected vehicle. The thin (3 mm) sheets “hiding” the heavily sloped lower casemate armor can be seen. Source: Soviet Heavy SPGs, 1941-1945 page 38.

Test results

The SPG was finished by mid-June of 1945. It was sent to Moscow Factory No.37, from where it was taken to the state proving grounds at Kubinka. Originally, testers noted that the fighting compartment was cramped but later changed to praises for the commander’s and driver’s stations and their placement. The People’s Commissariat of Armaments asked to move the Object 704 to the Leningrad Artillery Research Experiment Range, to test the gun and artillery capabilities. Despite this, the vehicle was still sitting in Kubinka. A test program letter for the ML-20SM was also sent in July 1945. It was only in August when tests were approved but only began by September because Factory No.172 engineers did not arrive at the testing grounds. They finally arrived by the 24th of September, only to leave a few days later, leaving behind only an engineer which did not have authorization for any testing work! This outright comical timeline of bureaucracy delayed the testing of the Object 704 by six months. By the 13th of November, Kuznetsov and chief designer Nazarov finally arrived from plant No. 172. Testing was done from October until the 13th of November, through which 65 shots were fired for indirect fire and 244 shots for direct fire.

A letter summarising the results and opinions after tests was published.

  • Loading tray: No complaints other than the corners should be rounded, to make passing between the loader’s station and the breech operator easier.
  • Sights: The TSh-17 was comfortable and in a good position in relation to the gunner’s eye. The offset of the sight was negligible after 40 shots (it is safe to assume after more shots, the offset would be noticeable).

Fighting compartment notes

Several interesting remarks were made in relation to the superstructure and the design of the fighting compartment.
– The gun mantlet had no access port for the much-needed recoil brake. This meant that measuring the hydraulic fluid and releasing air was impossible.
– The hole below the gun mantlet (for depression of the gun) accumulated water.
– The sloping on the side walls made stowing ammunition difficult and complicated. Making the walls vertical was suggested.
– The headlight was mounted on a solid mount. Because of this, it shattered during firing trials. A movable spring stand was recommended.
– The commander’s position was praised, it was put facing forwards and the new hatch made battlefield observation easier and more effective.
– Both the gunner’s and driver’s stations were praised and deemed as an improvement over previous heavy SPGs.
– The loader’s position was actually considered spacious. The report stated that taking out the 12 rounds next to him could be done with ease. However, the 7 rounds on the opposite wall were noted to be hard to reach and load.
– In contrast, the breech operator’s station was noted to be cramped, especially when the gun was traversed to the left, bringing the breech to the right. Extracting the 16 propellant charges to the right side of the tank was not ideal due to the tight space. The other 4 charges beneath the gun were impossible to take out in combat conditions.

Other conclusions were:
– Wear on the barrel and muzzle velocity drop was typical, considering the caliber of the gun. After 309 rounds (244 of which with maximum charge), muzzle velocity dropped by 0.8%.
– The muzzle brake simplifies production and improves observation of the target after firing.
– Recoil brake performance is satisfactory, but the problems with access to it still stand.
– No unexpected wear or deformation occurred on the gun.
The gun had no malfunctions with the exception of failure to extract shell casings that had been used several times (as much as 10 shots).

Conclusion and fate

The Object 704 had clear advantages over the ISU-152. These included the lack of a muzzle brake, improved protection, and position of the driver and commander. The issues that were found, could, and most likely would have been addressed, if it would have entered production. The tank’s entry in service was hindered by bureaucracy and failure to get it to testing. The loss of time meant that the IS-4 was nearing serial production, making the IS-3 and a SPG based on it obsolete. With hindsight, the story of the IS-4 is, arguably, even worse. Another heavy self-propelled gun would not be built until the Object 268, based on the T-10, which had a similar fate to the Object 704.

The single prototype built survives today at Kubinka, where it was brought for testing in 1945. Source: World War II Wiki

You can also watch a walk around of the exterior and interior of the vehicle, made by “The Chieftain”, Nicholas Moran, here 

Illustration of the Object 704 by Pavel Alexe, based on work by David Bocquelet, funded through our Patreon campaign.

Sources:

Tankmuseum.ru
Heavy SPGs 1941-1945, Soliankin, Pavlov, Palov, Zheltov
Zveroboy, Mikhail Baryatinsky
Warspot.ru
Tankarchives.ca
Topwar.ru
Heavy SPG, A.V. Karpenko

Categories
WW2 Soviet Prototypes

Object 257

Illustration of the Object 257 by Pavel Alexe. The similarity to the suspension of the M4 Sherman can be seen.

USSR (1945) Heavy tank – none built

The IS-7 (Object 260) is one of the most well-known tanks developed by the USSR, in part due to its massive size and weight, placing it with the likes of Tiger II. However, few know about its lengthy and intricate development process, consisting of many years of work and prototypes, with a total of seven different prototypes sharing the name IS-7. One of these was the Object 257, the bridging in between the failed IS-6 and the renowned IS-7.

‘Baby’ IS-7

In February of 1945, a replacement program for the Object 701 (IS-4), which had just started development seven months earlier, was requested by the GABTU (Main Directorate of Armored Forces). The SKB-2 factory, which designed the Object 701, was too busy with it and was working on its production. This left a window of opportunity for Factory No.100 to take over and begin work on the IS-4 replacement. Factory No.100 had just lost to SKB-2, as the Object 252 and 253 (IS-6) were deemed inferior in many ways to the Object 701. An upgrade to the Object 252, known as the Object 252U, was made in November of 1944, using pike-shaped angled armor with help of engineers from NII-48 research institute. However, the changes were not able to revive the already canceled IS-6. Despite its failure, it served as a good basis for the upcoming heavy tank.

Illustration of Object 252U, on which Object 257 was largely based. Illustration by Pavel Alexe.

On 7th April 1945, requirements for a 122 mm tank gun with a muzzle velocity of 1,000 m/s (3,280 fps), two-part ammunition, and a rate of fire of four rounds per minute (15 seconds reload) were issued. Factory No.100 had already done work with OKB-172 on the BL-13 gun which was used on the late alterations of the Object 252 and 252U. Earlier prototypes of the IS-6 had the D-30. This new gun was called BL-13-1 and featured improvements over the BL-13, such as a mechanical gun rammer, increasing its rate of fire to a whopping 8-10 rpm. Even a mechanical autoloader was tested, but, despite its claimed solid reliability, it was sluggish and was not worth losing a crew member on. It also decreased the rate of fire to 7-8 rounds per minute at a higher price tag. Nonetheless, the idea was never fully dropped, as the final IS-7 prototype used a loading assistant, using a conveyor belt. The shells were however larger, as the gun had a 130 mm caliber.

Work started on the new heavy tank in May 1945 with P. P. Isakov, who had previously worked on the Object 252U and IS-2U projects, as chief designer. The turret was taken directly from the Object 252U, and so was the pike-nose design. The engine and transmission, rather interestingly, were taken from the Object 253, the IS-6 variant which used a mechanical-electrical transmission, which caught fire during trials, was expensive and unreliable. The biggest change was made to the lower hull and suspension. This project would get the designation Object 257 and was the first design to get the name IS-7.

Design

As mentioned earlier, many elements from the IS-6 program were used in Object 257. The turret and pike nose came from the Object 252U and the engine and transmission from the Object 253. However, one of the main focuses of the Object 257 project was sturdier protection. The same principle applied on the pike nose, which was implemented on the side of the hull as well. The previously flat hull sides were now angled inwards at an extreme angle, forming a diamond shape silhouette from the front and rear. On the downside, this caused huge internal problems. Primarily, torsion bars could no longer be used, since the hull was too narrow, meaning that the suspension had to be moved on the outside of the hull. For the suspension, four volute springs were mounted on each bogie, with two wheels per bogie, a very similar design to that of the American M4 Sherman. This made the Object 257 one of the most unique looking Soviet heavy tanks of the post-war era, as this was the first time a Soviet tank used volute spring suspensions.

The turret was identical to that of the Object 252U, being heptagonal and of a low profile. Inside, the gunner was seated to the left of the gun, with the commander behind him. The loader was located to the right of the gun. A coaxial machine gun was also mounted to the right of the gun, and could be fired by the gunner. It is unclear if it was a 7.62 mm SGMT machine gun or a 12.7 mm DShk heavy machine gun. The loader was responsible for loading this weapon as well.

Cutout line drawing of the Object 257. The pike nose armor can be seen. The problems created by the armor layout and low profile are clear. The gun has little room to depress and the driver is very cramped. 5th June 1945. Source: Yuri Pasholok

Crew

As the Object 257 focused mainly on protection, crew comfort and overall ergonomics of the tank had to be sacrificed. The pike-like front end of the vehicle decreased the amount of space available for the driver. As shown in the drawing, the driver’s pedals would be located high up, his feet being on the same level as his torso. This would have been uncomfortable, especially when driving for longer periods of time. The driver had an entry and exit hatch on top of him, however, it was directly under the gun, meaning that entering and exiting would have been frustrating when the barrel was over the hatch. To add to his misery, he only had one periscope, relying more on the commander for command.

The gunner and commander could sit on chairs mounted to the floor through a long arm. Even for them, the conditions were not great. The low turret profile gave them very little headroom, not to mention it restricted the main gun from depressing more than a few degrees. The commander’s position lacked a cupola, and only had one periscope facing forwards and one backward. This further limited his visibility.

Cutout front and rear view of the Object 257. Many interesting details are made clear here, such as the Y-shaped seat support and interesting ammunition placement. Source: Yuri Pasholok

The loader was to the right of the gun, having to push the shells in with his left arm, a rather large inconvenience, considering the size and weight of a 122 mm shell. In addition, the ammunition was made out of two parts, the shell and the cartridge. In a turret bustle at the back, 30 rounds were stored, protected by an armored case. The cartridges were stored along the sides of the hull, diagonally, meaning that if one cartridge was taken out, another could possibly slide down. This, however, is only speculation. The average loader could load the gun in around 15 seconds. More warheads were stored in the hull, behind the driver. All this meant that the loader could easily load in the warheads, but had to bend down to grab a cartridge. As indicated earlier, an autoloader system was designed, however, despite its reliability, it was slow. If an autoloader was used, it is unknown if the loader would have been dropped or he would have had other tasks.

Armor

One of the most interesting aspects of this tank is the armor layout. The pike nose was an increasingly common feature in Soviet heavy tanks of the time. It was 150 mm (6 inches) thick, angled at 28° from the side. Yet the lower hull was completely new. Instead of flat plates, like on the IS-6, the plates were angled inwards, forming the same effect as a pike nose. This would have helped immensely against incoming rounds, deflecting them into the ground. The top parts were 150 mm (6 inches) thick and angled at 30°. The bottom plates were 85 mm (3.3 inches) thick angled at 23°. This thickness was not maintained all the way to the bottom of the hull. Halfway in, the armor was thinned down to only 20 mm (0.8 inches) yet kept at the same angle. This was most likely done to save weight, as the chances of enemy fire hitting this area were rather low, with the large suspensions being in front. The new side armor was impenetrable to the German 105 mm Flak 39 and the front was even strong enough that the BL-13-1 gun could not penetrate it at point-blank range. The turret armor was thick as well. The sides, although tinner in some areas, since they were curved, were 150 mm (6 inches) thick, angled at 45° degrees. Of course, this came at a cost. The weight of the hull increased to 23 tonnes (25.3 tonnes) over the IS-6’s 21 tonnes (23 tonnes).

Side armor comparison of various Soviet heavy tanks of the time. The newly introduced IS-3 was rather small compared to the Object 257. Consider that, at that stage, the Object 257 was still called IS-7 (ИC-7). To the right, the Object 701 (IS-4) hull can be seen, which was, at the time, the most heavily armored Soviet tank. The IS-6 (ИC-6), on which the Object 257 is based, is in the top right. Source: Yuri Pasholok

Suspension

If there is something that makes the Object 257 stand out, it is the suspension. As previously stated, the lack of room in the hull meant that the suspension had to be moved on the outside. Curiously, a bogie with four volute springs per wheel was used. These were very similar to the M4 Sherman medium tank, and it is entirely possible the design was derived from it. The wheels were mounted on opposite sides of the bogie and had arms on either side. These arms would then be attached to two volute springs that compressed when the wheel moved upwards.

M4 Sherman in Soviet service. The Russians used American equipment throughout the war. This was likely the inspiration source for the suspension on the 257.
Source: The Sherman Tank Site

Engine

As the weight had been increased up to 55 tonnes (60 US ton) on paper, a new engine was needed. Since 1944, Factory no.77 had been working on a new engine, based on the V-2, called V-16F. It was coupled to a similar (if not the same) electric transmission used on the Object 253. However, this engine was deemed very poor. Trials took place between March and May of 1945 and it was found to be unreliable. Even supercharging the engine to 600 or 750 hp that the IS-6 and IS-4 had would have put a huge strain on the engine, and failures occurred. Even at 520 hp, the engine was faulty. However, an engine this underpowered would have been disastrous if mounted on a 55 tonnes heavy tank, considering a 50 km/h (31 mph) speed was wanted. Further development was done on the V-16F, however, efforts were abandoned, and improved V-12 engines were used on the further IS-7 project.

The unreliable and weak V-16F engine initially proposed for the Object 257. Considering its many issues, it was left behind and V-12 engines were re-used in the IS-7 program.
Source: Yuri Pasholok

New German heavies and Conclusion

After the discovery of the Maus and Jagdtiger and their analysis, the armor on the Object 257 was deemed insufficient. The 128 mm KwK 44 guns of the Jagdtiger and Maus would have pierced the hull. Likewise, the armor on the Maus and Jagdtiger was too strong for the BL-13. All this meant that the Object 257 needed to be reworked significantly. In addition, on 11th June 1945, the requirements of a new heavy tank were set by the GABTU. The weight increased to 60 tonnes (66 US tonnes) and the new armament was to be an S-26 130 mm gun. Lastly, torsion bar suspension was required. The Object 257 clearly was not adequate, leaving factory No.100 to start work on a new heavy tank. Nonetheless, work was not in vain, as the experience gained and armor features of the Object 257 were passed on. Many other tanks were designed, until the final Object 260 was made, the IS-7 we know today.

Illustration of the Object 257 by Pavel Alexe. The similarity to the suspension of the M4 Sherman can be seen.

Sources

https://warspot.ru/2793-elektrostalin-6
https://warspot.net/9-object-257-the-first-is-7
http://www.tankarchives.ca/2019/03/modernization-on-paper.html

Object 257 specifications
Dimensions (L-W-H) 7.375 x 2.430 x 3.390 meters
(24 x 9 x 11 feet
Total Weight, Battle Ready 55 tonnes (60 US tons)
Crew 4 (Commander, Gunner, Loader and Driver)
Propulsion V-16F engine and electrical transmission
Speed 50 km/h (31 mph)
Armament 122 mm BL-13-1 2-part ammunition gun
co-axial 7.62 mm SGMT machine gun
Armor Hull armor
Front top plate: 150 mm at 28°
Front bottom plate: 150 mm at 40°
Side top plate: 150 mm at 30°
Side bottom plate: 85 mm & 20 mmTurret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
Total Production 0; blueprint only
Categories
WW2 French Prototypes

ARL 37 ‘Char de Rupture’

ARL 37 Variant V. The odd dome shaped casemate and the small unmanned turret are what made Variant V such an unusual design.

France(1937)
Heavy tank – none built

The 1930s was a period of rapid re-armament and tank development. Many European nations were focusing on developing and improving their own tank forces, leading to more and more specialized and advanced fighting vehicles. France was not to be left behind, reorganizing part of its defense industry and starting new tank projects. The need for a new French heavy tank was amplified with the start of the construction of the German Siegfried Line, a defensive wall running across the German border with France, vis-a-vis the Maginot line.

This prompted the French Conseil Consultatif de l’Armement (Armaments Advisory Council) on 4th May, 1936, to start a new heavy tank program. The technical requirements for the new tank, named “Char de Rupture 1937” (roughly translating to breakthrough tank), were released on 12th November 1936. The Conseil Consultatif de l’Armement stated the following:

“Char lourd, très protégé et très armé, propre en particulier à être utilisé défensivement et offensivement dans la guerre en région fortifiée”.
(Eng: “A heavy tank, well armored and well-armed, suitable for both defensive and offensive purposes in fortified battlefields.”)

The main focus was the armor and armament. In Char B1 fashion, there were two main armaments, one in the hull and one in a fully rotating turret. The armor was to be able to resist anti-tank cannon fire from as close as 200 meters (220 yards). In addition, the top speed was requested at 30 km/h (18 mph) and a range of 200 km (125 miles) or 10 hours. The total weight was to not exceed 45 tonnes (49.6 short tons)

In the spring of 1937, three French companies presented their designs: AMX, FCM and ARL.

Ateliers des constructions de Rueil

ARL was the only company that had not designed tanks before. In 1935, the Docks de Rueil, originally part of APX (Ateliers des constructions Puteaux) were renamed to Ateliers des constructions de Rueil (abv. A.R.L.) after nationalization. It was also then that the design bureau was created. Located in the suburbs of Paris, the workshop became more famous post-war, with the construction of the ARL 44, yet participated in the design of many other French tanks.

Triplets

Unlike its competitors, which presented the AMX 37 and FCM F4, ARL presented three designs simultaneously, the Variant C, Variant S and Variant V. Every version had different turrets, armaments and layout. It is important to note that blueprints of the rear of the hull do not exist. It is unknown if they were ever made or potentially lost, however, all the existing blueprints are on the armament layout, showing that they were supposed to use the same hull. Ultimately, the engine used and similar details are unknown. All three variants were, speculatively, based on the same hexagonal-shaped hull, with large tracks running over side skirts, similar to the Char B1. In addition, all versions had a flamethrower mounted in the hull, on the right side, to compensate for potential blind spots.

75 mm APX howitzer model 1929

The gun used inside the hull was the 75 mm APX howitzer mle 1929. Originally made for the Maginot Line as a static defense, it was developed from the infamous Model 1897 75 mm howitzer. It was later adapted for use in armored fighting vehicles and used in the later ARL V39 prototype. This gun was also used by the other competitors, FCM and AMX.

Side view plans of the gun mount in the ARL 37 (in this case, Variant C). The driver was also the gunner, as he had to traverse the entire tank to aim the gun, since it only had 5° of traverse. This arrangement was also present on the Char B1. Elevation and depression were better, at +18°/-15°.

Variant C

The most simple (from a mechanical and design perspective) out of the three, Variant C, was very similar to a Char B1 Bis. Besides the hull-mounted gun, a 1-man turret was mounted on the left side of the hull roof. The turret was very similar to the APX-1 turret on the Somua S35 and Char B1 Bis, however, the armor was greatly improved, at approximately 100 mm (4 inches) all around. Inside the turret, a 47 mm SA35 gun was mounted, the same gun as on the Char B1 Bis and Somua S35. The ammunition used would have most likely been the same Obus de Rupture Mle 1935 (AP model 1935) weighing 1.62 kg (3.6 pounds). The entire shell was 325 mm long (13 inches) while the projectile was 145 mm long (5.7 inches) and the case was 193 mm long (7.6 inches). On the Char B1 Bis, the muzzle velocity of the SA35 was 660 to 680 m/s (22 feet per second) with a penetration of 40 mm angled at 30° at 400 m. Variant C carried 106 rounds of ammunition for the 47 mm, 98 in the hull, and 8 in the turret.

It had a crew of four, a driver, responsible for driving the tank, but also aiming and firing the 75 mm gun. Behind him in the hull was the loader of the 75 mm gun. In the turret was the commander, responsible for commanding the tank, spotting targets, loading, and firing the 47 mm gun. This was a common feature of French tanks of the period. At the end of the crew compartment, a mechanic was seated. Quite common on WWI tanks, this position was archaic by 1937 standards. In practice, he would have been in charge of passing ammo up to the commander and fulfilling other, smaller tasks. He would have also been in charge of the radio, of unknown type, yet it is likely to have been the ER-53, used on Char B1s.

Side views of a SA35 gun from a B1 Bis tank. Source: Warspot
Side view of the crew compartment of the ARL 37 Variant C. The thick armor and crew layout can be seen.
Source: Chars Francais
Top view of the ARL 37 Variant C. The similarity to the Char B1 Bis is discernible.
Source: Chars Francais

Variant S

The second design proposed was more complex than the previous, and the plans available are even more scarce. The small turret was replaced with a larger, three-man turret. However, this increased the crew to six men. The turret was cast into a large octagon, still with 100 mm thick sides. In contrast to Variant C, it was equipped with a 47 mm mle 1934 gun, which was also designed for use on the Maginot Line. It fired APX mle 1936 Obus de Rupture (Armor-Piercing High-Explosive, APHE) shells, with a muzzle velocity of 880 m/s and could penetrate 77 mm (3 inch) of armor angled at 30° at 500 m (547 yards) and 56 mm (2.2 inch) of armor at 1,000 m (1,094 yards). The shell weighed 1.670 kg (mock warhead, translation from the French “fausse ogive”) and the charge weighed 610 g. It is hard to tell why two different guns were chosen for different designs.

The main turret had a smaller, rotating pseudo-turret or cupola for the commander. This was equipped with two machine guns, most likely 7.5 mm MAC 31, however it lost the machine gun mounted parallel to the main gun, like in the Variant C. The commander would now stand in this cupola and be able to more effectively scan the environments and engage infantry.

As the crew expanded to six men, the layout changed. The turret now had a designated commander, gunner, and loader. Meanwhile, inside the tank, the driver, loader, and mechanic were the same. The designated gunner and loader would have vastly increased the efficiency of the tank. However, these changes would have made Variant S vastly more expensive compared to Variant C.

Side cutout view of the Variant S turret. While the majority of the turret was still 100 mm thick, the cupola was thinner.
Source: Chars Francais
Top view of the Variant S turret. The much larger size of the turret is obvious, most likely taking much of the space on the hull roof.
Source: Chars Francais

Variant V

The most complex and interesting of the three designs was Variant V. The turret was now unmanned and was equipped with a 47 mm SA35 (same as on Variant C) and two 7.5 mm MAC machine guns mounted coaxially, on each side of the gun. As it was unmanned, it was made much smaller. To aim and fire it, a device was created by Lorfeuvre, that would allow the commander to aim and fire the guns in the turret, and even the 75 mm in the hull, from a dome-like casemate to the right of the 47 mm turret. To cover up the blindspot that was created by the casemate, an additional 7.5 machine gun was added, facing the rear.

The crew was now five men. There was a driver (it is unclear if the 75 mm howitzer could be aimed and fired by both the driver and the commander) and two loaders, one of which was also designated as a mechanic. They shared the task of loading the 47 mm and 75 mm. Despite being unmanned, the turret did not have an autoloader, the technology did not exist in 1937. Rather, the loader was underneath the turret and loaded from there. The commander was located in the dome-shaped casemate and the radio operator was on the right of the tank, “inside” the side skirt in between the tracks.

Cutout side view of Version V. The small unmanned turret and large, dome shaped casemate can be seen. Note the gas canister for the flamethrower in the bottom right.
Source: Chars Francais
Top view of Version V. The crew positions are clear, however how the two loaders (the two men sitting in line behind the driver) operated is hard to tell. Most likely, one passed on the ammunition, while the other loaded. Yet the interior seems roomy, so they could move around more in combat. The location of the radio operator, inside the track side skirts, gives information on the mysterious hull design. Since there was enough space to fit a man inside, it means the suspension most likely used leaf springs. Coil springs would be too large, like in the AMX 37, where the coils took up the whole height of the sideskrit.
Source: Chars Francais

Version V was a very unorthodox design, clearly being expensive and more complex than the other variants. The ARL 37 would have been extremely expensive no matter what, its undoubtedly large size, thick armor, and need for a massive engine would have made this program very expensive, let alone the complex devices needed on the Version V.

Hull

The largest mystery with the ARL designs remains the hull. Since no complete blueprints exist, it is hard to tell how it looked. From the existing blueprints above, we do get a clear image of how the front looked, and that it had small, leaf spring suspension, like many other French tanks of the time. The rear of the hull was never designed, as it included the engine, transmission, and other parts that did not exist and would be subject to change. Nonetheless, the ARL V39, a tank destroyer built by ARL in 1939, is clearly based on the ARL 37 and is a good clue to how the ARL 37 may have looked like.

Yet the ARL V39 was 25 tonnes lighter, had only 50 mm of armor, and used 190/240 hp engines, completely different from the heavy tank. The ARL designs, and the FCM and AMX proposals all “used” non-existent engines. The FCM and AMX designs weighed over 50 tonnes and required two V12 engines of unknown power.

The ARL V39 self-propelled gun prototype. Despite being a good 25 tonnes lighter than the AMX 37, it was inspired from the designs of the AMX 37 and would be a good indicator of how the ARL 37 looked like.
Source: Pinterest

Conclusion

Each variant of the ARL proposal tried to fix larger, underlying issues. Variant C was the “standard” French design, akin to the Char B1 Bis. However, the overworked commander and gunner/driver would have been a huge drawback, as proven on the B1. Variant S tried to fix this, by having a larger, three-man turret. Yet the larger turret proved to be very wide and it did not fix the overworked driver issue. Variant V eased out the work for the driver, however, now the commander had to aim two guns, and still relied on the driver to traverse the tank when aiming the 75 mm howitzer. All in all, it proved that multi-gunned tanks were not a good idea.

Just like the other competitor’s designs, the ARL variants failed. The entire project was deemed too expensive and the tanks could only be produced in small numbers. Logistical and reliability issues might have appeared when building such a large vehicle with engines made from scrap. The weight and size of the ARL variants are unknown, however, they most certainly went over the 45 tonnes mark. A final blow came when the Conseil Supérieur de la Guerre (Eng: Superior War Council) decided on 26th March, 1937 that a much smaller, cheaper yet heavily armored tank would be designed instead. This in turn went south as well, when the Section de l’Armement et des Études Techniques (Eng: Section for Technical and Armaments Studies) made a study which showed that a tank fulfilling those criterias was already under development, and there would not be a need of a new program. This tank was the Char G1.

The ARL 37 would continue to influence the ARL V39 Self-propelled assault gun, and in February of 1938. the requirements of a heavy breakthrough tank changed. Most importantly, the weight restriction was removed. This led to the development of the ARL 39 and ARL Tracteur C super heavy tanks.

ARL 37 Variant C. Note that the appearance of hull is mostly speculative.
ARL 37 Variant S. The significant difference between the SA35 and Model 1934 gun is clear. Observe the cupola with 7.5 mm MGs.
ARL 37 Variant V. The odd dome shaped casemate and the small unmanned turret are what made Variant V such an unusual design.

Sources:

Chars-francais.net
DGA Châtellerault
TNT number 11
Chars De France, Jean-Gabriel Jeudy
Memoiredeshommes.sga.defense.gouv.fr
Wikimaginot.eu
Modernfirearms.net

ARL 37 specifications
Variants C S V
Dimensions (L-H) 7.52 x 2.86 meters 7.52 x Unknown 7.52 x 3.12 meters
Total Weight, Battle Ready 45+ tonnes*

 
Crew 4 5 6
Propulsion Unknown; its competitors used 2x V12 engines
Speed 30 km/h*
Range 200 km*
Suspension Leaf Spring
Armament 1x 75mm model 1929 (11+ rounds)

1x 47mm CA-35 (106 rounds, 98 in hull and 8 in turret.

1x 7.5mm MAC

 1x 75mm model 1929 (11+ rounds)

1x 47mm Mle 1934

2x 7.5mm MAC

 1x 75mm model 1929 (136 rounds)

1x 47mm CA-35 (114 rounds)

3x 7.5mm MAC (5400 rounds)
Armor 100 mm (4 inch) all around
Total Production 0; partial blueprints only
Categories
WW2 Soviet Prototypes

Object 252 Improved, ‘Object 252U’

Illustration of Object 252U, on which Object 257 was largely based. Illustration by Pavel Alexe.

USSR (1944) Heavy tank – none built

The Last breath of the IS-6

In the later years of the Second World War (‘The Great Patriotic War’ to the Soviets), there was a quest to develop a replacement for the IS-2 heavy tank. The development process resulted in the IS-6 (Object 252/Object 253) and IS-4 (Object 701). This program was as secret as it was ambitious, with two rival factories working on their designs in absolute secrecy in fear of leaking information to one another.

On paper, the IS-6 seemed superior to any Panzer in Germany’s arsenal at the time. However, due to its mechanical issues and overall poor performance, it lost to its competitor, the IS-4, which would go on to enter service in 1946. Despite this, a last ditch effort to revamp the IS-6 was made, with limited success. This renewed vehicle would become known as the Object 252 November improvement – more commonly known as the Object 252U.

Name

The Object 252 upgrade from November 1944 might have never gotten an official designation. Yet modern historians and video game company Wargaming have called it Object 252U, with the ‘U’ probably coming from the romanized Russian word ‘улучшенный’ (uluchshennyy). For simplicity’s sake, we will refer to it as Object 252U for the rest of the article.

Development

After the battlefront experiences of 1943, with the appearance of the new German heavy tanks and tank destroyers such as the Ferdinand, the Soviet Union quickly realised that a new heavy tank was needed. Thus, in November of 1943, the GABTU (Main Directorate of the Armed Forces) requested the development of a 55 tonnes (61 tons) heavy tank.

Two factories of the same organization (ChKZ) and the same city, Chelyabinsk, were assigned this task.

1. SKB-2, which was headed by Nikolai Dukhov, who had taken part in the development of the IS tank, and would later become the assistant of the chief designer of the Soviet atomic bomb plan. SKB-2 designed the Object 701, which was a planned upgrade of the IS-2 and later became the IS-4.

2. Experimental Factory No. 100, which was headed by Josef Kotin, who previously had done work on countless Soviet tanks. In contrast to their ‘opponents’, they developed a completely new tank, the Object 252 and 253.

From June to October 1944, Factory No.100’s Object 252 and Object 253 (IS-6) failed in comparison to the SKB-2 design. The armor was much thinner than that of the Object 701, yet it was still heavy, weighing over 50 tonnes (55 tons). The mechanical problems in the suspension and mobility were worse compared to its heavier counterpart. Kotin managed to get the IS-6 to Moscow, where it got tested against the Object 701, but to no avail. In late November of the same year, an upgrade attempt was made with the help of the NII-48 institute using a heavily angled pike-nose design for the armor and a new turret. Despite it being a dead-end when it came to the development of the IS-6, it was a turning point for future heavy tank designs. This is now known as the Object 252U.

Outline of the November, 1944 Object 252 upgrade, commonly known as Object 252U. The U comes from the romanized Russian word улучшенный, meaning ‘improved’. It is hard to tell if this is an original name or a modern designation. Despite the improved armor effectiveness, the IS-6 boat had sailed, and the IS-4 was chosen for mass production.
Source: Warspot.ru
Object 252U frontal view. The low profile of the tank is even more clear from this view. Source: Stalin Supertanks IS-7

Design

Naturally, the design of the 252U was similar to that of the Object 252, as it was based on the same hull. Unmistakable are the large stamped steel wheels with a 750 mm (30 inches) diameter. These were first tested on the Object 244 (an IS-2 upgrade) to be used on the Object 252. The Object 253, although also an ‘IS-6’, used regular IS style wheels. The engine and the rear and side of the hull were untouched on the November improvement. The torsion bars suspension would remain the same too.

The engine would most likely have been the same as on the Object 252, a V12U diesel engine producing 750 hp at 2,100 rpm. The internal fuel tanks had a capacity of 650 liters (172 US gallons) but, in typical Soviet fashion, there would have been 4x 100 liter (26 US gallons) external fuel tanks on the sides.

Interesting to add is that the early designs for the IS-6 actually had a rounded frontal hull, similar to that of the much later Object 279, yet having a similar effectiveness to the Object 252U. The actual prototypes had a hull made of angled flat plates, probably because it was much easier and cheaper to produce compared to a large casting.

Early drawings of the IS-6 with a UFO-like shape, akin to the much later Object-279
Early drawings of the IS-6, by that time considered as an “IS-2 upgrade”. The curved hull that transpired onto the Object 252U is somewhat apparent.
Source: Stalin Supertanks IS-7
Factory No.100 IS-2 upgrade proposals. In the middle is the IS-2, while to the left is the rounded hull version and to the right is the flat plates version. This latter one would then become the IS-6.
Source: Warspot.ru
Object 252 with its larger road wheels. These large roadwheels, designed by N.F. Shashmurin proved to be faulty on the IS-6 – needing replacements every 200 to 300 km. In fact, 14 of these wheels were replaced during its 825 km testing. Note the BL-30T gun, which was to be replaced by the BL-13T. However, this idea never left the drawing board.
Source: Bron Pancerna, Flickr

The most notable changes appeared in the hull and turret. The NII-48 institute strongly suggested that, in order to improve the protection yet not increase the weight, a pike-nose design should be used. This meant two diagonal plates were welded in the front, creating a pike-like shape and greatly improving the effective armor on the front of the vehicle from threats directly in front of the vehicle. This was designed by engineers V. I. Takarov and G. N. Moskvin, which went on to later design the Object 257 as well.

Previously, the Object 252 and 253 used the D-30T 122 mm gun. This offered very little improvement over the standard D-25T from the IS-2, yet the price was almost doubled. As a result, a new gun was planned to be added to the Object 252, although it ended up never being fitted. The new gun was the BL-13 122 mm, developed in December of 1943 by OKB-172 and was a combination between the D-25T and the BL-9 gun barrel. Further work was done between Factory No.100 and OKB-172, with the gun being ready by July 1944. The capabilities of this weapon are unknown. A ready rack for the massive projectiles was located in the rear of the turret, covered by a thin protective casing, an overall design similar to modern MBTs. A total of 18 warheads were stored here. The casing with explosive material was stored within the hull, on the exact opposite side. This made loading the warheads relatively easy, however, the placement of the cases required the loader to bend down, and manhandle them up into the breech.

The new turret and BL-13T gun that was to be mounted on the IS-6. The tiny space between the top of the breech and the roof of the turret indicates extremely poor gun depression.
Source: Weaponsandwarfare.com

Crew

As the Object 252U was, for the most part, very similar to the IS-6, the crew compartment was mostly identical. It had a crew of four, a commander, gunner, loader and driver. The gunner sat to the left of the gun with the commander behind him. They seem to have shared the same entry and exit hatch, which could be fatal for the gunner in case of a need to evacuate quickly, as he would have to wait for the commander to exit first. The commander had no cupola to look out from, rather just two periscopes (one pointing forwards and the other backward) on top of his hatch. This would have made the commander almost blind when buttoned up. The commander was also in charge of the radio. The loader, as discussed above, had a tough time when loading the main gun. As the cases for the rounds were in the hull, he would have needed to get off his chair and lift them up. Since the turret had no basket, the crew members in the turret could either sit on seats attached to the turret or stand on the hull floor. The loader seems to also have been tasked with the operation of the 12.7 x 108 AA DhSK heavy machine gun. To operate it, the loader had to expose himself, by partially climbing out of his hatch. It is also entirely possible that he was also responsible for loading the co-axial machine gun, a 7.62 mm SGMT. The driver was located in the hull, with the hatch directly underneath the gun, potentially making it very difficult to exit, if the gun was pointing forward.

Since the Object 252U put such a large emphasis on protection, crew comfort and ergonomics were sacrificed. The angling of the hull armor plates made storing ammunition and overall life inside cramped and claustrophobic. An awful thought for many western tankers, Soviet tank design doctrine often sacrificed crew comfort for protection or a low silhouette.

If the IS-6 or Object 252U would have entered service, it would have most likely received a series of upgrades to fix the problems mentioned above, like the periscopes. The Object 701 had its periscopes altered and more added several times until full scale production. However, the armor profile and no turret basket were still features of future Soviet heavy tanks.

Armor

It was regarding armor that the IS-6 struggled the most in comparison with the IS-4. The front was one 100 mm (4 inches) thick flat plate angled at 65°. The lower front plate was 120 mm (4.7 inches) thick, yet only angled at 52°. The side armor at the thickest, was 100 mm. Testing was done in Kubinka, Moscow with captured German 88 mm and 105 mm guns, which could not penetrate the upper frontal plate from 50 m (55 yards). The 120 mm lower plate, being less angled, was penetrated from a “shorter distance”. These results, while being better than the IS-2 and IS-3, fell short of the protection offered by the IS-4. In this regard, the new pike nose design of the Object 252U came into play, as the lower plate was still 120 mm thick, but more sharply angled at 28°. The two upper plates forming the pike nose were 100 mm thick, yet angled at 16° from the side. This increased the effectiveness of the armor significantly. The rest of the hull remained the same as that of the regular IS-6.

Testbed of an IS-6 hull after firing tests possibly using German guns. Despite being well angled, the protection was not deemed strong enough, considering its weight. Note the heavy interlocking plates. It might come apparent that there is no access hatch for the driver. This, however, was a simplified and shorter mockup, purely designed to test the effectiveness of the angled armor. Having a full-size hull, with hatches and other components would have been too costly and time consuming for this purpose.
Source: Stalin Supertanks IS-7
Testbed of the IS-6 hull after firing tests, view from the side.
Source: Stalin Supertanks IS-7

IS-2U

With the help of NII-48, Factory No.100 also designed the IS-2U simultaneously with the Object 252U, making an IS-2 with a pike-like front hull. An improved version of the IS-2, it featured a new gun, and the pike-nose frontal armor. Like the Object 252, it was rejected, in favor of SKB-2’s Kirovets-1, which later became the IS-3.

Blueprints of the IS-2U, sometimes erroneously used to show Chinese heavy tanks. Although the program itself was different to the Object 252U, the pike-nose armor was designed by the same engineers, Tarotko and Moskvin.
Source: Warspot.ru

Fate and Conclusion

The Object 252 November upgrade never went past the blueprint stage, as the fate of the IS-6 had already been sealed. Yet, despite being unsuccessful, the design was not in vain. Instead, it served as a basis for the Object 257, which in turn led to the IS-7 heavy tank, the heaviest Soviet tank ever built. More importantly, it was one the first Soviet designs to implement the pike-nose design, which became famous with the IS-3, and was implemented in the majority of Soviet heavy tanks until their discontinuation.

Illustration of Object 252U by Pavel Alexe, funded through our Patreon campaign.

Sources

Supetanki Stalina IS-7
https://warspot.ru/2793-elektrostalin-6
https://warspot.net/9-object-257-the-first-is-7
http://www.tankarchives.ca/2019/03/modernization-on-paper.html

Object 252U specifications
Dimensions (L-W-H) 7.50 x 2.4 x 3.3 meters
(25 x 7.8 x 10.8 feet)
Total Weight, Battle Ready 50+ tonnes
(55 tons)
Crew 4 (Commander, Gunner, Driver & Loader)
Propulsion V12U diesel engine, 750 hp at 2,100 rpm
Speed 35 – 50 km/h (hypothetical)
(21 – 31 mph)
Range 400km
(249 miles)
Armament 122 mm D-13 2-part ammunition gun
12.7 x 108 mm DShK heavy machine gun on roof
co-axial 7.62 mm SGMT machine gun
Armor Hull armor
Frontal plates: 100 mm forming pike nose at 16°
Lower plate: 120 mm angled at 38°
Upper side plates: 100 mm angled at 45°
Lower side plates: 100 mm at 90°
Upper rear armor: 60 mm at 60°
Lower rear armor: 60 mm at 30°
Upper hull armor: 30 mm
Floor armor: 20 mmTurret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
Total Production Blueprint only
Categories
WW2 French Prototypes

FCM F4

France (1937)
Heavy Tank – None Built

Back in the 1930s, the tank was still a relatively new weapon. The masterminds of the world’s most powerful tank forces were still debating about its role on the battlefield. Fits of paper fantasy showed engineers and designers putting on as much armor and as big of a gun onto a tank as their imagination could manage. The inventions’ power and potential seemed limitless to the minds of many, leading to the emergence of a type of heavy tank more akin to a land battleship. Most countries capable of building tanks were experimenting with their own models, from the British A1E1, Soviet T-35, to the German Neubaufahrzeug, to name the more “practical” designs.

During the same time period, the Germans were building the infamous Siegfried Line or ‘Westwall’, a fortified defensive line consisting of bunkers, tank traps, and much more arrayed along the western German frontier. Nothing in the French tank arsenal was able to challenge these potent defenses. Combining the multi-turret tank designs – in fashion at the time – and this new threat from the east, the French quickly realized they needed a new powerful breakthrough heavy tank able to withstand anti-tank fire and destroy static defenses.

Breakthrough Heavy Tank

With the doctrine of breaching the Siegfried Line in mind, a heavy tank program was requested by the Conseil Consultatif de l’Armement (Armaments Advisory Council) on 4th May 1936. The specifications for this new program, named “Char de Rupture 1937” (literally breakthrough tank), were released on 12th November 1936. The Conseil Consultatif de l’Armement requested:

“Char lourd, très protégé et très armé, propre en particulier à être utilisé défensivement et offensivement dans la guerre en région fortifiée”.

“A heavy tank, well armored and well armed, suitable for both defensive and offensive purposes in fortified battlefields.”

The tank was to have a maximum weight of 45 tonnes (49.6 short tons) and dual armament, with a main gun in the hull and a secondary gun in a rotating turret. The vehicle would need thick armor, capable of resisting incoming fire from anti-tank field guns at a distance of at least 200 m (220 yards). Requirements for the mobility and speed of the design were tight, with a top speed of 30 km/h (18 mph) and a range of 200 km (125 miles) or 10 hours.

A few months later, in 1937, three French companies presented designs, AMX, ARL, and FCM.

Forges et Chantiers de la Méditerranée

The Forges et Chantiers de la Méditerranée (Eng: Foundries and Shipyards of the Mediteranean), better known as just ‘FCM’, was a naval shipyard that specialized in heavy vehicles founded by the British engineer Philip Taylor in 1853. Besides building large warships, like the Paris battleship, they had produced tanks and armored vehicles before, such as the FCM 36 and Char 2C.

One of the FCM shipyards at Seyne-sur-Mer. Source: Wikimaginot.eu

In May 1937 , FCM presented their first design for this competition (FCM was last of the three to present a design), the FCM F4 Variant A. The company already had plenty of experience in building large heavy tanks, as 10 years earlier it had designed the FCM 2C, one of the largest tanks ever made. The company also proposed designs for the program that would eventually become the Char B1, in the form of the FCM 21.

Design

Variant A of the FCM proposal was based on their previous heavy tanks. It had a large, frusto-conical turret located on the front of a long hull, with large idlers and drive sprockets beneath. Its suspension was typical of French heavy tanks of the time. On each side, there were eight bogies with one leaf spring each. To each spring, two road wheels were mounted. In addition, on each end of the track, there were two road wheels connected to bump stops for driving over rough terrain, such as trenches. They did not touch the ground, however, they helped minimize the impact when the tank first came in contact with an obstacle.

The turret housed a 75 mm gun, while a 47 mm gun was mounted in the hull. This allowed for more effective usage of the 75 mm, as it could cover an area of 360° around the tank rather than being restricted by the limited traverse of a hull-mounted weapon. This, however, meant that a larger turret had to be made, pushing the height of the tank to over 3 meters. This turret was frusto-conical, typical of FCM turret designs of the era and had a rotating cupola with a rangefinder on top. The 75 mm gun had a designated gunner and loader in the turret, while the driver was in charge of aiming, shooting and loading the 47 mm. The commander was located in the center of the hull, so it might have been possible for him to assist the driver with loading the 47 mm gun, but this is uncertain as no plans of the crew layout exist. The overall weight would have been around 55 tonnes – far above the requirements.

Armament

While ARL and AMX went with a ‘traditional’ Char B1 layout of a 75 mm howitzer in the hull and a 47 mm gun in the turret, FCM went on its own path. Just like on the Char 2C, they mounted the required 75 mm gun in the turret. It is unclear what 75 mm gun this was supposed to be. Some sources claim it was the same as on the Char 2C, the Model 1897 75 mm howitzer, while others state the 75 mm Model 1929 would have been used. The APX 75 mm model 1929 howitzer was a modified version of the Model 1897 75 gun, with many components, such as the barrel, being the same. It was originally built for the Maginot Line as a static defense, but later modifications allowed it to be mounted on combat vehicles. The later tank destroyer projects ARL-V39 and Somua SAu 40 were also equipped with this gun. Likewise, the designs of FCM’s competitors, ARL and AMX, also mounted the newer howitzer in the hull.

The ammunition used is unknown, however, the same guns in the Maginot Line used HE model 1917 rounds with a muzzle velocity of 577 m/s. Ammunition stowage for all the weapons is unfortunately also unknown.

Tank gun mount of the 75mm mle 1929 howitzer, the same was used on the later Somua SAu 40 and ARL V39 tank destroyer projects. Source: Wargaming

As secondary armament, FCM used the 47 mm model 1934 gun, firing APX mle 1936 Obus de Rupture (Armour-Piercing High-Explosive, APHE) shells. Originally, just like the APX mle 1929, this gun was intended for the Maginot Line. These shells had a muzzle velocity of 880 m/s (2890 fps) and could penetrate 77 mm (3 inch) of armor angled at 30° at 500 m (547 yards) and 56 mm (2.2 inch) of armor at 1000 m (1094 yards). The shell weighed 1.670 kg (mock warhead, translation from the French “fausse ogive”) and the charge weighed 610 g. This gun would have been aimed and loaded by the driver. This was common in French tanks and was done to reduce the number of crewmen needed per vehicle. However, naturally, this put the crew under a lot of strain and required more training. In addition, maintaining the tank with a smaller crew was more strenuous.

Version A was equipped with 2 machine guns (later versions would have up to 6) and these were the 7.5 mm MAC (Manufacture d’Armes de Châtellerault) model 1931. Originally built for use in static defences on the Maginot Line, it could also be mounted on tanks and other Armored Fighting Vehicles (AFVs). It was gas operated and fired the 7.5 mm MAS cartridge from a 150-round drum magazine. These rounds had a muzzle velocity of 830 m/s (2,700 ft/s). Its weight of nearly 12 kg (26,45 lb) meant that it had to be mounted on a heavy steel mount.


The 7.5 mm MAC 31 with a tank mount. The large 150-round side-mounted drum magazine meant that storage inside of vehicles (in this case tank) was simple and allowed for continuous fire, without the crew having to reload very often. This was crucial in French tanks as the crew already had a lot of tasks to fulfill. Source: Wikipedia

Engine

There is very little information on the mechanical parts of the FCM design. It is known that it was to be equipped with two V12 diesel engines. It is unclear what engine this would have been, but may be assumed this engine was being purpose-designed for this tank project and got canceled simultaneously. Each engine drove an electric generator that was connected to the final drive, similar to the later British TOG 1 and 2, and the German Elephant tank destroyer and Maus super-heavy tank. These engines were supposed to have allowed the 55 tonne tank to reach 30 km/h.

Armor

Like many other statistics about this vehicle, the armor thickness is mostly unknown. However, considering that the AMX design had 100 mm (3.94 in) at the front around the turret, it is relatively safe to assume that the FCM F4 would have had similar armor thickness. French tanks also tended to have the same armor thickness all around the turret. The frontal hull plate was well angled, and so was the turret, which increased its effectiveness.

Other Variants

After presenting the first version, FCM showed a second one, the FCM F4 Variant B. It was identical but had the transmission and exhaust moved centrally and an FCM 36 turret equipped with 2 machine guns was added, facing the rear. This increased the weight to 57 tonnes and the crew to 5. There are no images of this design.

In August 1937, FCM proposed 2 new designs. Version C had a new turret, also armed with a 75 mm gun. Version D had the 47 mm gun in the hull moved into the little turret in the back. In October, Version E was designed with 5 additional machine guns. Finally, in December, Version F was shown mounting a flamethrower and the total weight was pushed to 59 tonnes.

From Heavy to Super Heavy

All 3 companies – ARL, AMX and FCM – had their designs rejected because the tanks would have been too expensive and could only be produced in small numbers, therefore they would not have any large effect on the battlefield. To solve this, the Conseil Supérieur de la Guerre (Eng: Superior War Council) decided on 26th March 1937 to build a smaller and cheaper yet heavily armored tank. However, after testing, the Section de l’Armement et des Études Techniques (Eng: Section for technical and armaments studies) claimed that this would be redundant, as there was already such a tank under development – the Char G1.

Due to this evolution, the requirements were changed in February 1938. There was to be no weight limit and a 75 mm gun had to be mounted in the turret. The same companies presented designs once again, however, these new specifications were very close to those of the original FCM design, so the Supreme Command gave FCM a contract to build the tank. This would eventually lead to the FCM F1, a 140 tonne monster with 2 massive turrets and a 90 mm gun. However, by the time a mockup was ready in 1940, France had been occupied by Germany and, consequently, all super-heavy tank designs were halted, meaning no French Char Lourd (heavy tank) would ever get the chance to batter the Siegfried Line.

FCM F4 Version A. The large turret and the rangefinder can be seen. Note the 4 holes in the sideskirts acting as mud shoots, to release mud from under the sideskirt.
Source: Pinterest


Illustration of the FCM F4 produced by the Author, Pavel Alexe, and funded by our Patreon campaign.

Specifications
Dimensions 7.5 x 2.94 meters
(24.6 x 9.65 ft)
Weight 55+ tonnes
(60.63 tons)
Crew 4 (commander, driver, loader, radio operator)
Propulsion 2 x V12 diesel engines connected to electrical generators
Maximum speed 30 km/h* (18 mph)
Suspension Leaf springs
Range 200 km* (125 miles)
Armament 75 mm model 1929
47 mm SA35
7.5 mm MAC

*These numbers are what was requested by the Conseil Consultatif de l’Armement . Actual numbers are unknown.

Sources

Chars-francais.net
DGA Châtellerault
TNT number 11
Chars De France, Jean-Gabriel Jeudy
Memoiredeshommes.sga.defense.gouv.fr
Wikimaginot.eu
Modernfirearms.net

Categories
WW2 French Prototypes

AMX 37 ‘Char de Rupture’

France (1937)
Heavy Tank – None Built

During the mid-1930s, Germany started construction of the Westwall, otherwise known as the Siegfried Line. This fortification spanned across the German border with France up until their border with Denmark and was equipped with numerous bunkers and cannons. The French authorities were alarmed by this and figured that they would have to overcome this defensive line. However, no tank in the French arsenal at the time was able to combat such an obstacle. Therefore, they quickly started a heavy breakthrough tank program, named ‘Char de Rupture 1937’.

Specifications

On the 4th of May, 1936, the Conseil Consultatif de l’Armement (Armaments Advisory Council) requested plans for a new heavy breakthrough tank that would be able to charge the Siegfried Line while being able to knock out static defenses and enemy tanks. A quote from the Council:

“Char lourd, très protégé et très armé, propre en particulier à être utilisé défensivement et offensivement dans la guerre en région fortifiée”.

“A heavy tank, well armored and well armed, suitable for both defensive and offensive purposes in fortified battlefields.”

The exact specifications were released on the 12th of November 1936. The tank was to have a maximum weight of 45 tonnes (49.6 short tons) and be equipped with two main armaments, a 75 mm gun and a 47 mm one. As it was supposed to lead the charge against bunkers and fortifications, it was to have thick armor, namely to withstand anti-tank fire from 200 m (220 yards). The mobility aspect was optimistic for a tank of the time, as it was supposed to reach 30 km/h (18 mph) while having a range of 200 km (125 miles) or 10 hours of operation.

By May 1937, 3 companies presented their designs, ARL, FCM, and AMX.

Construction d’Issy-les-Moulineaux

Construction d’Issy-les-Moulineaux (AMX) was created when the French government took over the Renault factories in 1936, ultimately meaning that the Char de Rupture AMX was one of their very first tank projects. AMX went on to design and build some of the most famous post-war French tanks, like the AMX-13, AMX-50 and AMX-30.

Production line of AMC-34 on the left and Renault D1 on the right, in the Ateliers de construction d’Issy-les-Moulineaux (Renault) before nationalization, 1935. Source: Wikipedia Commons

Design

In March of 1937, AMX presented its preliminary concept for the program. This was essentially an enlarged Char B1 Bis. Their design was elongated, with a 75 mm gun mounted in the hull to the right of the driver. On the roof, a small turret with a 47 mm gun and a machine gun were placed. There were two turret designs, the first one having the gun mounted on the right side and an unusual polygonal shape. The second turret was much more similar to that of the Char B1 bis and Somua S35, the APX-1, however, the armor on it had been increased considerably. As a matter of fact, the entire tank was covered in thick armor and, in typical French fashion, long side skirts were hiding the suspension, leaving only the massive tracks exposed. It had a crew of 4, driver, tank commander (located in the turret, manning the 47 mm gun) a loader and a radio operator. To reach the desired top speed, two V12 engines were to be used, each engine being coupled to an electrical transmission which, in turn, drove four electric engines, two per sprocket.

Artist’s impression of the AMX 37, most likely made to promote the design. Like many images of the kind, the proportions and details are off. The turret is of the late-type. Source: aviarmor.net

Original blueprints of the AMX 37. The resemblance to the Char B1 can be seen, with the large sprocket, side skirts and weapon placement. Note that the turret seen is the early type. Source: memoiredeshommes.sga.defense.gouv.fr
Front view of the tank. The mounting of the 75 mm model 1929 howitzer and the turret’s location can be seen. Source: memoiredeshommes.sga.defense.gouv.fr

Top view. Note the large, exposed tracks and odd polygonal turret shape. Source: memoiredeshommes.sga.defense.gouv.fr

Armaments

Just like in the Char B1, AMX mounted a 75 mm howitzer in the hull and a 47 mm gun in the turret. The 75 mm gun was the APX 75 mm model 1929 howitzer, a modified version of the famous Model 1897 75 mm gun, with many components, such as the barrel, being the same. It was originally built for the Maginot line as a static defense gun, but later modifications allowed it to be mounted on combat vehicles. The later tank destroyer projects ARL-V39 and Somua SAu 40 were also equipped with this gun. It was mounted to the right-hand side of the driver who was also the gunner. The main drawback was the poor gun traverse, only 6° to the left and right.

The APX 75 mm Mle 1929 on the mount designed for tanks and other AFVs. Source: Wargaming.net

The gun mounted in the turret was most likely the 47 mm SA35, the same gun used in the turret of the Char B1 Bis. It would have shot the same type of ammunition, the Obus de Rupture Mle 1935 (AP model 1935) weighing 1.620/1.625 kg (3.6 pounds). The entire shell was 325 mm long (13 inches) while the projectile was 145 mm long (5.7 inches) and the case was 193 mm long (7.6 inches). On the Char B1 Bis, the muzzle velocity of the SA35 was 660 to 680 m/s (22 feet per second) with a penetration of 40 mm angled at 30° at 400 m.

Side views of the SA35 from a B1 Bis. The mantlet mounted at the base of the barrel would be different on the AMX 37. Source: Warspot

The machine guns used on the tank were the 7.5 mm MAC (Manufacture d’Armes de Châtellerault) model 1931. Like many other French weapons of the time, it was developed to be mounted on the Maginot line, but was later adapted to be mounted on armored fighting vehicles and tanks. It was gas-operated and fired the 7.5 mm MAS cartridge from a 150-round drum magazine mounted on the left side of the gun. This large magazine meant that the crew did not have to reload as often compared to other machine guns (the German MG-34, when mounted on tanks and AFVs, had a 50 to 75 round magazine). Such a large magazine was crucial in the already overworked French tank crews, of which the AMX 37 certainly was not an exception. These machine guns were attached independently, next to the 75 mm and the 47 mm. Two more MAC machine guns were placed in ball mounts, next to the entrance doors on the sides of the tank, to better protect from infantry sneaking up on the tank. Due to the large suspension of the tank, the side machine guns had restricted traverse.

The 7.5 mm MAC Mle 1931 with a tank mount. The large 150-round magazine can be seen. Source: Wikipedia

Crew

Despite a large number of weapons, the tank only had a crew of four; driver, commander, loader and radio operator. In a similar fashion to the Char B1, the driver was also the gunner for the 75 mm howitzer. Since the gun only had 6° of traverse, the driver had to turn the entire tank to better aim the gun. The loader was loading the 75 mm and was located in the hull. He was also responsible for loading and firing the MAC machine guns to the right of the tank and the one coaxial to the 75 mm. Behind the driver was the turret and that was where the commander sat. He was responsible for searching for targets, firing and loading the 47 mm and, to top it all off, fire and load the co-axial MAC machine gun. The radio operator, located behind the commander, was in charge of the radio of unknown type, and the machine gun to the left of the tank. He could have also assisted the commander, giving him ammunition from the hull up and into the turret.

It was typical for French tanks to have one-man turrets, or to have overworked crews. The sheer amount of work that the commander had to do in the AMX 37, and many other French tanks of the time, was huge. He did not only have to command the tank and spot targets for the 75 mm gunner through his cupola, but he also had to aim, load and fire his 47 mm and, when necessary, the machine gun as well. This lead to an overworked soldier, having to complete so many tasks at once and doing neither very well. The reasoning behind this design was to decrease the amount of manpower needed to operate tanks. The fewer men you need per tank, the more tanks you can have. The shortage of men was deemed an issue in France during the 30s, as the population still had not recovered from the First World War. In practice, the French had overworked crews, and too few tanks, getting the worst out of both.

Top view of the crew compartment. The four crewmen’s position can be clearly seen with the driver, commander and radio operator sitting in a row with the loader on the far right. Note the two hull MGs overlooking the sides. Another interesting detail is the floor escape door most likely used by the driver or when another door was damaged, as the other three crewmen have their own doors. Separating the crew compartment and the engines is a pneumatic, waterproof, firewall door, which could be used to access the engine from within the tank. Source: memoiredeshommes.sga.defense.gouv.fr

Turret

The tank had two different turrets during its development process. The early version had an octagonal faced, frustoconical shape, with the SA35 47 mm gun mounted on the right side and the 7.5 mm MAC on the left. Its armor values are unknown, however, they are probably similar to those of the second design turret. This second design was much more similar to that of the Char B1 Bis, a nonagon with the 47 mm mounted more centrally and the machine gun mounted slightly to the left. The armor was 100 mm all around and 43 mm on the roof. While it can be hard to distinguish the two turrets from one another, the second design has large bulb-like protrusions on the sides for periscopes, which are not shown in many contemporary line-drawings and illustrations. The periscopes were surrounded by thick armor, doubled around the holes, as seen in the blueprints. This turret was designed in August, after AMX had submitted the first design. The reasoning behind why a new turret was made is unknown, and why it was re-done after the tank had been presented.

Several angles of the second version turret. Note the rear hatch for the tank commander. Source: memoiredeshommes.sga.defense.gouv.fr

Armor

The armor on the AMX design was very impressive. To be able to withstand AT fire, the frontal plate was angled at 50° and was 100 mm thick. It is a well-known fact that French tanks had thick armor, but this was another level for 1937. The turret was just as impressive, 100 mm thick angled at 85° all around. The top of the turret and hull were 43 mm thick. To put this in perspective, the Somua S35 had 47 mm of armor at the thickest, while the Char B1 Bis had 60 mm and the Tiger tank – yet to even be conceptualized – was ‘just’ 80 mm all around the turret and not sloped! However, all of this armor came with additional weight and made the 7.25-meter long tank weigh above 45 tonnes, the maximum weight allowed.

Original blueprints of the late turret. Besides the gun, traverse mechanism and more, the extremely thick armored walls of the turret can be seen. Source: memoiredeshommes.sga.defense.gouv.fr

Propulsion

When the tank was designed, there were no engines in production in France powerful enough to move such a heavy vehicle at the required 30 km/h. This meant that completely new engines had to be designed. The tank was to be equipped with two V12 engines with a horsepower of 550 hp (600 hp according to other sources). As per the blueprints, two companies were taken into consideration in the production of these engines; Aster and CLM (Compagnie Lilloise des Moteurs). These engines were to be mounted horizontally along the length of the tank, right behind the ammunition storage. Each engine was coupled to an unknown type of electrical generator connected to two electric engines (total 4, 2 per side) that drove the sprockets. For traverse, each sprocket had a diagonally mounted traverse motor. Neither CLM nor Aster produced such large engines at any point.

Cutout view of AMX 37 showing the V12 Aster motors, however, only one can be seen as they are mounted parallel one to the other. In this image, the crew compartment and other details can be seen. Note the traverse motor mounted diagonally by the final drive. The armor thickness can also be seen.
Front view of the V12 Aster motors. Note the gigantic coil springs from the suspension.
The in-line CLM engines. It was a much shorter alternative compared to the Aster engine however, it was much taller. It is unclear if these engines had fewer pistons, usually in-line engines need to be significantly longer than V shape engines to have the same number of pistons.
Front view of in-line CLM engines. Due to the narrow, tall shape, it is safe to assume these were in-line piston engines. The large plate-like shape over the engines is the radiator, of which this tank had 3. Source for these 4 images: memoiredeshommes.sga.defense.gouv.fr

Suspension

The suspension was very similar to that of the Char B1, with 16 small steel road wheels per track. Two wheels in the front (in between the idler and road wheels) and one in the back (in between the sprocket and road wheels) were not touching the ground and, when tensioned, moved diagonally. This was done to decrease the shock when the tank crossed over large obstacles. On each side, there were 4 large springs connected to a bogie. Each bogie then had two smaller bogies in turn connected to two wheels. In addition, every single wheel had its own spring. This was a very complex system, however, it allowed for a lot of motion from the wheel to the hull itself, meaning that the ride quality would have been rather smooth. At the top of the tracks, 10 return rollers were mounted. This was rather unusual for French tanks, as the Char B1, for example, still used skids.

Cutout showing the suspension layout. This system was very similar to the British Matilda Mk.II tank. The track tensioning system can also be seen.

Aftermath

Despite all the efforts, the Conseil Consultatif de l’Armement rejected all the designs presented by FCM, ARL, and AMX. All three companies presented very complex and expensive tanks, thus limiting their production output to a very small number; making them insignificant on the battlefield. To add insult to injury, every company exceeded the 45-tonne mark, even on paper. The AMX 37 weighed around 50 tonnes on paper, however, a battle-ready tank would have even exceeded this already high number. In response to this issue, the Conseil Supérieur de la Guerre (Eng: Superior War Council) decided on the 26th March 1937 that a much smaller, cheaper yet heavily armored tank be designed. This in turn went south as well, when the Section de l’Armement et des Études Techniques (Eng: Section for technical and armaments studies) made a study which showed that a tank fulfilling those criteria was already under development, and there would not be a need of a new program. This tank was the Char G1.

This was not the end of the road for AMX designed heavy tanks. In February of 1938, the requirements changed. Amongst others, the weight limits were removed. This would eventually lead to the AMX Tracteur C super heavy tanks, but like its predecessor, it remained on paper only.


Illustration of the AMX 37 ‘Char de Rupture’ (Breakthrough Tank), produced by the author, Pavel Alexe, and funded by our Patreon campaign.

Specifications
Dimensions 7.25 x 2.70 x 2.94 meters
(24.6 x 8.9 x 9.65 ft)
Weight 50+ tonnes
(55 tons)
Crew 4 (commander, driver, loader, radio operator)
Propulsion 2 x V12 or in-line diesel engines connected to electrical generators connected to electrical motors
Maximum speed 30 km/h* (18 mph)
Suspension Coil springs
Range 200 km* (125 miles)
Armament 75 mm model 1929
47 mm SA35
4 x 7.5 mm MAC
Armor 100 mm in front hull (3.9 inches)
100 mm side skirts
100 mm all around the turret
43 mm top of the hull and turret (1.7 inches)

*These numbers are what was requested by the Conseil Consultatif de l’Armement . Actual numbers are unknown.

Sources

Chars-francais.net
DGA Châtellerault
TNT number 11
Chars De France, Jean-Gabriel Jeudy
Memoiredeshommes.sga.defense.gouv.fr
Wikimaginot.eu
Modernfirearms.net
Tbof.us