Two Tanks In One

A story of what a Main Battle Tank is and how it came to be.

Tanks evolved considerably over the course of over 100 years of service. The first tanks were built to break through enemy fortifications, but still ended up being much smaller than the landships that H.G. Wells dreamed of. Nevertheless, the effect they had was considerable. All armies of the world wanted to have their own tanks, but not all managed to create one. A tank only seems simple, but in reality is quite a complicated fighting machine that requires a powerful industry to produce. Far fewer nations managed to build their own tanks than their own aircraft. In addition, like any weapon individual tanks quickly became obsolete. It is only in the last few decades that tank development slowed down from its breakneck pace. Tanks remain one of the key types of vehicles on the battlefield. There have been many attempts to write them off as a relic of the past, but practice shows that this time has not yet come.

T-72, the most numerous Main Battle Tank. These tanks were developed in the late 1960s but continue to serve and will do so for decades to come.

KV-13 Trials

 "To the Chief of the 6th Department of the GABTU BTU, Engineer-Colonel comrade Kovalev

RE: the condition of the KV-13 as of October 19th, 1942

I report the following on the condition of the KV-13 as of October 19th, 1942:

1. The tank set out on its sixth trip on October 18thm 1942, during which it drove for 120 km. The following defects were discovered:
   
1. The 2nd gear is difficult to engage
2. The main clutch slips
3. The track slipped off, damaging the drive sprocket rim
4. The front road wheel assembly (axle, swing arm, torsion bar tube) was lost
5. The batteries were not charged
6. The steam valve of the radiator expansion tank releases water heated to 110-115 degrees instead of steam
7. Not a single gear could be engaged at the end of the run due to the main clutch adjustment slipping. The vehicle had to be towed to the workshop.
2. When the clutch was disassembled, it turned out that the driving clutch plates were badly deformed. The driven plates had deep scuffs on their working surfaces.
   The loss of the road wheel was caused by a bad attachment of the swing arm to the hull. This is a design defect.
3. The vehicle was disassembled for repairs.

The expected date for returning to trials is October 20th, 1942.

GABTU Military Representative, Engineer-Major Fedoseyev."

Via Yuri Pasholok

85 mm Gun Upgrade

 

"In order to make loading of the S-31 tank gun in the KV-1S and IS-1 tanks comfortable, the following must be done:

1. Increase the distance from the bore axis to the roof to 470 mm (280 mm on the IS-1) as ramming an 85 mm shell at face height is difficult and impossible if the gun is depressed.
   On most modern foreign heavy tanks and on our SPGs the space between the bore axis and the roof ranges from 400 to 500 mm.

An IS in the Hand

An experimental prototype of the IS-1 tank, formerly called KV-13, was sent to factory trials on March 9th, 1943. This was a fully fledged heavy tank, a little lighter than the KV-1S, but much more mobile and protected. However, during the government trials in the spring of 1943, it became clear that it needs a number of improvements, some of them quite serious. The German Tiger tank was the last nail in the coffin of the IS-1. It turned out that an 85 mm gun was necessary to combat this tank, which would not fit into the turret of the experimental Soviet vehicle. This was the start of the story of the Object 237, the last step towards the creation of the heavy IS tank.

Second to Last Step

The first prototype of the KV-13 heavy tank entered trials on September 26th, 1942. The vehicle was quite unusual. With the protection of a heavy tank, it had both the size and weight of a medium. This later caused many hypotheses about a "medium tank with heavy armour". In reality, the KV-13 was never a medium. It was developed as a heavy tank from the very beginning, and the small size and mass were a direct consequence of the requirements issued by the GABTU. For a number of reasons, work on the KV-13, which also earned the name IS-1 during its design, did not continue past a second prototype. However, it was an important milestone towards the creation of a next generation Soviet heavy tank.

Unlucky KV

Cases where vehicles that never reached mass production become milestones are common in tank building history. The Soviet KV-13 tank is one of those cases. This tank is often referred to as a "heavily armoured medium tank", which is incorrect. The KV-13 was designed as a heavy tank from the very beginning. The revolutionary vehicle satisfied the requirements of the Soviet military completely. This was the first maneuverable heavy tank that combined impressive armour with small mass, and, most importantly, high mobility.

The KV-13 appeared at a difficult time, which is a part of the reason why it did not enter production. Nevertheless, further Soviet tank development was influenced by the last design of the talented Nikolai Valentinovich Tseits.

KV-13, First Steps

"To Chief of the 6th Department of BTU, Engineer-Major Voroshilov

On the condition of the KV-13 as of September 30th, 1942, I report that:

1. On September 26th, the first factory trial began, a 20 km march. All components of the transmission and suspension worked well. Oil pressure dropped to 2 atm. as engine RPM increased due to a defect in the oil reductor valve. The defect was corrected after the trial.
2. On September 27th, a second trial was scheduled, a 25 km march. The following defects were discovered:
1. Worsening of the gearbox actuator on the 30th kilometer.
2. Three road wheel hubcaps were lost.
3. The water in the cooling system is hot, reaching 110-115 degrees with a temperature of 10-12 degrees outside.
4. Controlling the tank is difficult.
5. The engine does not increase RPM in 9th gear and works poorly.
6. All other tank mechanisms worked satisfactorily.
3. An M-1 car following the tank was used to gauge its speed. At 1800 RPM in 9th gear, the tank runs at 55 kph. This is almost the same as the estimated top speed (57.6 kph using a T-34 track).
4. Examinations after the trial showed the following:
1. The loss of hubcaps was caused by a design defect in the ball bearing in the wheel axle. The wheel could move along the axle relative to the ball bearings and hit against the hubcap. Not able to withstand the force, the hubcap bolts were torn off and the hubcap fell off and got lost. The design of the ball bearing in the wheel axle is being urgently reworked.
2. The gearbox actuator worsened due to a knocked off calibration of the main clutch. It was discovered that it is not possible to calibrate the main clutch without removing the radiator.
3. Difficulty in controlling the tank can be explained by necessary force of 60 kg on the levers and 90 kg on the main clutch pedal. The servo mechanism of the main clutch works poorly. The design of the controls is being urgently reworked.
4. The hand gas lever does not allow the third position of the multiplexor lever to be used.
5. The tachometer panel hits the driver's hand when the right lever is pulled to the maximum.
6. The air filter cannot be removed for cleaning without removing the oil radiators.
7. The turret travel lock disengages during movement.
8. The locks on the firing ports are unusable.
9. The track tightening mechanism travel is short and does not sufficiently tighten the tracks.
10. The balancer is attached weakly and can be turned.

Aside from the above, many small and easily correctable defects were discovered.

Most defects discovered during assembly, trials, and inspection after trials are corrected. Designers are making new blueprints with corrections to the tank's weaker points.

The tank should be disassembled for improvements and corrections of discovered defects.

GABTU Military Representative, Engineer-Major Fedoseev."

CAMD RF 38-11355-958

KV's Replacements

"Decree of the State Committee of Defense #1878
June 5th, 1942

On the improvements to KV-1 tanks

The State Committee of Defense decrees that experience in using the KV-1 tank in battle revealed the following drawbacks of the KV tank:

1. Its heavy weight at 47.5 tons reduces its combat value, and makes it more difficult to use.
2. The gearbox is insufficiently reliable due to insufficient robustness of the first and slow gears and gearbox case.
3. Insufficiently powerful cooling, as a result of which lower gears must often be used, which reduces the average speed and limits the full power of the diesel engine.
4. The visibility from the tank is insufficient, due to a lack of commander's cupola and inconvenient locations of observation devices.

In order to get rid of the aforementioned drawbacks, the State Committee of Defense decrees that:

1. The NKTP (comrade Malyshev), director of the Kirov factory comrade Zaltsmann, and chief designer, comrade Kotin, must ensure that as of August 1st, 1942, KV-1 tanks that weigh no more than 42.5 tons are being made.
2. Allow the following measures for the NKTP (Kirov factory), Uralmash factory, and factory #200 to reduce weight to 42.5 tons:
1. Reduce the thickness of side armour, LFP, and turret armour from 75 mm to 60 mm.
2. Remove the driver's plate armour screen.
3. Reduce the thickness of the floor to 30 mm.
4. Reduce the thickness of the cast turret walls and gun mantlet to 80-85 mm, as well as reducing the volume of the cast turret, keeping the turret ring diameter.
5. Reduce the track width to 650 mm.
   Until August 1st of this year, NKTP and Kirov factory are allowed to produce no more than 10 47.5 KV-1 tanks per day.
3. The NKTP, Kirov factory director comrade Zaltsmann, chief designer comrade Kotin, and GABTU must complete trials of the 8-speed gearbox KV tank by July 15th of this year and begin production of tanks with this gearbox on August 1st, 3 per day, starting on August 15th, 5 per day, and starting on September 1st, build only tanks with this gearbox.
4. Take into account the message from Kirov factory's chief designer about defects in the existing 5-speed gearbox being removed in the following ways:
1. A more robust design and stronger materials for the case.
2. Improved robustness of the first and slow gears due to the use of higher quality steel.
5. GABTU and comrade Fedorenko must finish replacing defective gearboxes by June 25th with improved gearboxes.
6. In order to improve cooling of KV-1 tanks in high temperatures, NKTP, comrade Malyshev, director of Kirov factory, comrade Zaltsmann, and chief designer of the Kirov factory, comrade Kotin must begin production of KV-1 tanks with new finned radiators, new fans with stamped blades, and machined fan cases by July 1st, 1942.
7. NKTP (director of the Kirov factory, comrade Zaltsmann) must provide GABTU with 50 finned radiators in July and 100 in August.
   GABTU chief comrade Fedorenko must ensure that old fans are replaced with new ones during major repairs.
8.  NKTP, comrade Malyshev, director of Kirov factory, comrade Zaltsmann, and chief designer of the Kirov factory, comrade Kotin must begin production of KV-1 tanks with commander's cupolas starting from September 1st of this year.
9. In order to ensure further weight reduction and increased speed of the KV-1, the NKTP (Kirov factory) is allowed to produce two KV-13 tanks according to the previous proposal:
1. Mass: no more than 35 tons
2. Armour
1. Sides: 60 mm rolled
2. Front (cast): 100 mm
3. Rear (cast): 80-85 mm
4. Turret platform (cast): 80-85 mm
3. Commander's cupola on the turret
4. Speed:
1. Highway: up to 50 kph
2. Off-road: 20-25 kph
5. Engine: 600 hp V2-K diesel
6. Armament: 76.2 mm F-34 gun and 2 coaxial DT machineguns
7. Ammunition: 60-70 76 mm shells, 2500-3000 DT rounds
8. Crew: 4 (commander and also radio operator, gunner, loader, driver)
9. Fuel range: 250-300 km on highway
   The rest of the requirements will be confirmed by NKTP and GABTU.
10. NKTP (comrade Malyshev) and Kirov factory (comrade Zaltsmann) must produce two experimental KV-13 prototypes by August 10th of this year, test them by September 10th of this year with GABTU and provide a report to GOKO regarding the trials and suggestions on producing the KV-13 at the Kirov factory by September 15th."

RGASPI 644-2-69

The rest of the decree isn't all that interesting (just shuffling around some industrial resources for the new armour), but Stalin's red pencil is at it again, and the KV-13 is crossed out for the time being. 

IS, First Series

"Order of the People's Commissar of Tank Production of the USSR #104ss
Moscow
February 25th, 1943

On the construction of experimental IS tanks

To fulfil State Committee of Defense decree #2943ss, issued on February 24th, 1943, I order that:

1. The director of the Kirov factory, comrade Dlugach, director of factory #200, comrade Sherbakov, and chief engineer of the Kirov factory, comrade Kotin, produce two experimental IS tanks at the Kirov factory: one with the 122 mm gun (U-11), the other with a 76 mm gun (F-34), and provide them for proving grounds trials by March 10th, 1943.
2. The GOKO decree defines the following main characteristics of the IS tanks:
1. A maximum weight of 39.5 tons for the tank armed with the 122 mm U-11 gun, including ammunition, fuel, and crew.
2. A maximum weight of 38.5 tons for the tank armed with the 76 mm F-34 gun, including ammunition, fuel, and crew.
3. Armour:
1. Front: 120/100 mm (cast)
2. Side: 90 mm (rolled)
3. Top and floor: 20 mm 
4. Rear: 60 mm (sloped at 45 degrees)
5. Turret: 100 mm (sides)
4. Maximum speed: 55 kph.
5. Transmission: 8 speed gearbox, planetary turning mechanism, planetary final drives.
6. Engine: 600 hp V-2K
7. Ammunition:
1. No less than 30 shells for the IS tank with a 122 mm gun.
2. No less than 80 shells for the IS tank with a 76 mm gun.
8. Crew: 4
9. Machineguns:
1. With a 122 mm gun: 2 (coaxial and hull)
2. With a 76 mm gun: 3 (coaxial, turret rear, and hull)
10. Fuel capacity: 500 kg

..."

CAMD RF 38-11355-1485

Heavy Tanks and Lightening

"To the Deputy People's Commissar of Defense, Lieutenant-General of the Tank Forces, comrade Fedorenko

Report.

On the issue of design and production of experimental heavy tanks, I report that:

The current heavy KV tank fielded by the Red Army demonstrates superiority in battle over fascist tanks with its powerful armour and armament. It can be successfully used to destroy the enemy defences, crushing them with its tracks and gun. The Patriotic war, combining in its nature a positional war with a maneuver war requires much of a heavy tank, and the KV does not fully meet those requirements. The KV lacks mobility for the following reasons:

1. A low maximum speed limits its ability to move between flanks to counter-attack.
2. Insufficient visibility from the tank makes orienting on the battlefield difficult.
3. The tank's mobility is decreased by its number of gears: five forward gears is not enough for a heavy tank.
4. The force required to shift gears is large. Momentum acquired on lower gears is wasted, and the tank must slowly accelerate in a higher gear.
5. The brake ribbons are insufficiently reliable and lead to the tank stopping on the battlefield and requiring repairs.

The usage characteristics of the KV are limited by:

1. The requirement for robust bridges or other means of crossing ravines or water hazards.
2. The requirement for powerful tractors for rapid evacuation from the battlefield, dragging out of ravines, traps, etc, or the use of more of these expensive vehicles.
3. The requirement of units to have powerful repair tools.

Based on the above, the government must task the People's Commissariat of Tank Production to order the Kirov factory and factory #183 to produce two experimental prototypes of heavy tanks with the following characteristics"

1. Combat mass: 30 tons
2. Crew: 4 (3 in the turret)
3. Armour:
1. front and turret: 90 mm
2. side and rear: 75 mm
3. roof and bottom: 25 mm
4. Armament:
1. 76 mm gun: 1
2. DT machineguns: 2 (one coaxial and one in the hull)
3. SMGs: 2 (PPSh)
4. Flamethrower: 1 (attachable instead of the hull machinegun)
5. Gun range:
1. vertical: -5 to +25 degrees
2. horizontal: 360 degrees
6. Hull machinegun range:
1. vertical: -5 to +15 degrees
2. horizontal: +/- 10 degrees
7. Ammunition capacity:
1. Shells: 50
2. Machinegun rounds: 2520
3. PPSh rounds: 1000
4. Flamethrower fluid: 20 shots
8. Engine: V-2 or V-2K diesel, 500-600 hp
9. Maximum speed:
1. Highway: 60 kph
2. Off-road: 25 kph
10. Off-road range, non-stop: 10 hours
11. Transmission: planetary
12. View: 360 degrees, provided to the commander with an observation hatch in the turret roof, optical sights (with exit eyepiece 10-12 mm and field of vision no less than 60 degrees), and doubled observation devices (in the roof) for the driver.
13. Communications:
1. External: quartz radio station
2. Internal: TPU-3 with throat microphone
14. The side reductors must be protected by main armour.
15. The coolant system and air filters should provide 10 hours of uninterrupted movement off-road in 45 degree heat.
16. The engine must be able to start without external heating at a temperature of -45 degrees.

A tank produced in accordance with the above requirements will be fully equipped for modern war and will be an even more deadly weapon against fascist tanks.

BTU Chief, Major-General of Tank Forces Korobkov

Representing the BTU Military Commissar, Engineer-Lieutenant-Colonel Kovalev

June 1st, 1942"

CAMD RF 38-11355-935

Seems that the "medium tank with heavy armour" concept surfaced again, two years later. If you look at the characteristics of the A-44, it matches these requirements exactly!

As for the products of Kirov factory and factory #183, those were, of course, the KV-13 and T-43. Neither vehicle ended up in production, but the KV-13 influenced the IS series and the T-43's turret migrated to the T-34-85. 

Soviet Air Filters

Many complaints are lodged against Soviet air filters (mostly based on the Americans mistreating a Pomon).

While the Pomon wasn't a perfect filter (it only cleaned the air to 80% purity at 1 gram per cubic centimeter), the Soviets already had a better filter in 1940: the "Vortex", planned for installation on the T-50. The Vortex, developed at factory # 174, could filter the air to 98% purity without being cleaned for 10 hours. However, the T-50 fate was rather unfortunate, and it was not made in large numbers. The filter was then successfully used on KV tanks, until it was replaced by the Cyclone filter. It was also used on early KV-1S tanks, SU-152 SPGs, and the KV-13.

Figure 44: "Vortex" type air filter, used on KV tanks. CAMD RF 38-11355-2543

The air is cleared by entering the filter at an angle, and forming a vortex, dropping the dust into the oil pan underneath. The Cyclone filter, Vortex's replacement, reverses the flow of air, dropping the dust out of it more effectively, like so:

I have previously mentioned the Multicyclone filter. Let's take a closer look.

CAMD RF 38-11355-1630

Multicyclone filters installed in the KV-1S (top) and IS tanks (bottom)

Even the Cyclone filter, which provided 99.4% air purity at air dustiness of 1 gram per cubic meter, was unsatisfactory to the Soviets. In May of 1943, a new filter was tested on the KV-13 (Object 233), which provided 100% air purity at dustiness of 3 grams per cubic meter, and could operate without cleaning for twice as long as Cyclone. 

The air filter was installed in all Soviet medium and heavy tanks from 1943 onward.

Birth of the IS Tanks Part 1: IS-85

Stalin's name started appearing on tanks long before the start of the war. In 1935, the first modernized T-28A tank was named "Stalin", but it was just the one tank. The BT-IS (Iosif Stalin) in 1936 and BT-SV (Stalin-Voroshilov) in 1937 were projects to increase the mobility and armour of the BT tank series, respectively. Neither project was accepted by the army.

Another project is seen in 1942, and it's certainly optimistic. It's definitely more like a KV-4 or KV-5 than anything associated with a production IS.

CAMD RF 38-11355-935

This tank has a mass of 100 tons, armour 120-150 mm thick, was armed with 3 machine guns (one was AA) and a 152 mm ML-20 gun-howitzer. A small secondary turret contained a 20 mm autocannon. The hull would hold two flamethrowers. The tank would be powered by two diesel motors, with a combined 1200-1500 hp, accelerating the tank to 24 kph, both forward and backward. The tank was crewed by 7-8 crewmen. This project was very much ridiculous, and was declined. 

The birth of the "real" IS tanks, the heavy breakthrough tanks that are very well known today, started in 1942. By then, the advantages of the once invincible KV-1 have diminished. New German long-barreled 75 mm guns and APCR ammunition for 50 mm guns were capable of penetrating its armour. Its mass, and thus sluggishness, became a great disadvantage. A smaller, faster KV was in development. Its armour was cast and angled. It was smaller than the KV-1, and not as long, with 5 road wheels instead of 6. With the same armour protection, this new vehicle was much faster than the old KV-1. Its projected speed was 55-60 kph. The tank was named KV-13 (Object 233). A prototype was finished by May of 1942, and started factory tests. The tank could reach a speed of 51.7 kph (still pretty good for a heavy tank). An interesting feature was that it could use a drive wheel and tracks from both the T-34 and KV-1, a lifesaver for repair crews that had to handle both types of tank.

This first prototype still carried the old Voroshilov name, but its direct successors did not. A report from the Chelyabinsk factories announced the decision to name the new tanks after Stalin.

The two new Stalin tanks were direct successors of the KV-13. Many internal components were reworked, but the hull and overall layout remained the same. The old friction clutches were replaced with planetary gear mechanisms. The cooling system was redesigned. The tracks (the new tanks used KV-1 tracks) were lightened. The two tanks were equipped with a ZiS-5-IS 76 mm gun and a U-11 122 mm howitzer, in a KV-9 turret. They were named IS-1 (Object 233IS) and IS-2 (Object 234IS). While being superior to the KV-1 in speed, reliability, and simplicity, these new tanks brought nothing new in terms of firepower.

IS-1 (right) and IS-2 (left)

In February of 1943, news of Tiger tanks on the Tihvin front percolated through the ranks. All those 107 mm guns that were made for hypothetical superheavy tanks suddenly became a lot more relevant. Stalin called Grabin, who was ready to resume the production of ZiS-6 guns at factory #92 in 15-20 days. In April of 1943, while the new IS tanks were still undergoing trials, an order was received by the ChKZ factory for two new heavy tanks. These tanks must be at most as heavy as a KV-1, have more armour (at least 100 mm), and possess an 85 mm high power gun (with a turret ring diameter of at least 1700 mm) and a 107 mm tank gun (with a turret ring diameter of 1850 mm).

On April 15th, 1943, order #3187ss demanded new tank guns capable of fighting new German tanks and SPGs. These guns, with a caliber of at least 85 mm, must penetrate 120 mm of armour at 600 meters, and with a caliber of at least 107 mm, 120 mm of armour at 1000-1200 meters. These guns already existed. The 85 mm ZiS-25 with a muzzle velocity of 1150 m/s and 107 mm ZiS-26 with a muzzle velocity of 1012 m/s were created, and even built, at factory #92, but never passed any trials. The design of tank mounts for these guns would take as much time as making new guns from scratch.

Using these requirements, two new tanks were developed: IS-3 (85 mm gun) and IS-4 (107 mm gun). The extra mass of these larger guns required a longer hull, and six road wheels. However, nobody made ammunition for the 107 mm gun since 1942. Factories lacked machinery to make new 107 mm shells, and the cost of one such shell would be enough to produce 2 85 mm shells or 3-4 76 mm shells. Existing stocks of 107 mm ammunition were mostly pre-revolutionary. The IS-4 was not an option.

Several 85 mm guns were developed to compensate. All guns were more or less equal ballistically, and competed in trials against each other. IS-1 was armed with a D-5T-85 gun. IS-2 was armed with an S-31 gun. Two KV-1Ses participated too: one with a D-5T-85 in an IS turret, one with an S-31 in the KV-1S turret. Despite the similarities between the ZiS-5 and S-31, which would have made production cheap and painless, the D-5T was selected as superior based on smaller size and weight. The tank carrying it was indexed IS-85, and accepted into production. The KV-1S with the same turret was indexed KV-85, and also accepted, to serve while production of new tanks gets off the ground.