Thursday 31 October 2013

Now banned in a whole country!

At 5:32 pm EST today, one of my readers from Russia has informed me that my blog is no longer accessible in the country, due to the following laws:
  • 114-FZ "On counteracting extremist activity"
  • 436-FZ "On protecting children from information harming their health or development"
  • 149-FZ "On information, information technologies, and protecting information"
  • Government Decree #1101 "Single register of domain names, links to pages in the information-telecommunication network "Internet" and network addresses, allowing the identification of sites in the information-telecommunication network "Internet", containing information the distribution of which is forbidden inside of the Russian Federation"
As the overwhelming majority of the content of this website actually comes from Russia in the first place, the irony is palpable. Finally, now I am in the same leagues as famous people like Madonna!

Russia is currently #10 on my list of countries sorted by visitors, with 1753 overall, 544 over the last month, and 120 this week.

Edit: now with screenshot!

It would appear that this did not propagate to all ISPs, as I am getting some traffic from Russia. 

PzII in Kubinka Archives

Here's a dump of materials from Kubinka's archives, regarding the PzII. Sadly, none of the other tanks in that same document dump have this level of technical detail explored, so this is all you get for now.

Component layout of the PzII tank

Main friction clutch of the PzII tank

Gearbox of the PzII tank 

Gearbox of the PzII tank

"Bosch" company inertial starter

PzII transmission knee joint

More PzII drivetrain components

And now, for regular photos.

Wednesday 30 October 2013

World of Tanks History Section: VK 16.02 Leopard

The history of this “feline” tank, which, despite its long project cycle, was never built in metal, began before WWII, in the summer of 1938. That is when German companies MAN and Daimler-Benz started developing a scout tank, designated VK 9.01. Formally, it was considered a further development of the PzII, but was actually a brand new project. The prototype was built in 1939. After field tests, a “zeroth” series of 75 tanks was planned, designated PzII Ausf. G. However, between April 1941 and February 1942, only 12 tanks were produced. In 1940, the prototype, now designated VK 9.03. was modernized with a 200 hp Maybach HL 66p engine. The maximum speed of the tank reached 60 kph, which was considered enough for a scout tank. In April of 1942, MAN built a 12.9 ton VK 13.03 prototype, meant to replace the VK 9.01/9.03. It was tested at Kummersdorf along with other tanks (including the T-15 Skoda), and was then accepted by the army as the Pz II Ausf. L Luchs (Sd. Kfz. 123). An order was placed for 800 tanks of this type.

The VK 16.02 Leopard was going to be the only vehicle in the new “gefechsaufklarer” (combat scout) class, replacing the VK 16.01 (Pz II Ausf J). In the middle of 1942, MAN began work on the Leopard, to fulfil a contract of 5 pre-production samples. By the end of November, blueprints for a wooden mockup were ready. The hull had sloped armour and was reminiscent of a shorter version of the Panther tank, developed by the same company.

Daimler-Benz was developing a prototype as well. It had a rear transmission, as was typical for Soviet tanks, with a forward turret. However, Daimler-Benz lost the Panther project to MAN. The development of a shorter version of the VK 30.02 DB was also terminated.

New tank projects were controlled by Wa Prüf 6 (Waffenamt Prüfwesen 6 / Panzer- und Motorisierungsabteilung 6th department of Arms Directorate). In order to reduce the workload of MAN engineers, whose primary job was the Panther, Leopard's blueprints were given to MIAG in January of 1942. Two variants were proposed: a light scout, weighing 18 tons, and a heavy one, weighing 26 tons. On June 4th, 1942, both were presented to Hitler. He selected the 26 ton variant, as more appropriate for the realities of modern war. On July 27th, 1942, MIAG presented the blueprints for Fko 252 Gefechsaufklarer Leopard to Wa Pruf 6. These are the blueprints that would have been used if the Leopard was every built.

In September of 1942, Arms Directorate decided that the first Leopard should be ready for April 1943, and in October 1943, 20 of these tanks should be produced monthly. These plans were not meant to be, again, by Hitler's will. On October 13th 1942, he met with Reichsminister Speer. During the meeting, it was established that combat scouting duties can be done by the Panther tank, which were of a higher priority. The situation changed, and the tank must be lightened in order to reach 60 kph. The first Leopard prototype never made it to metal. On January 3rd, 1943, the VK 16.02 was cancelled, as a tank that did not meet the requirements of 1943. The concept of combat scouting was continued with the VK 28.01 by Daimler-Benz, with a new engine and thicker armour, but this project also never left paper, and the program was shut down in May 1944. The turret developed for the Leopard was used in the Sd.Kfz.234/2 Puma. Rheinmetall tried to use the Leopard chassis and a 10.5 cm leFH howitzer to make a self propelled "Waffentrager Leopard" gun, but only a wooden model was built.

Currently, several plastic models are produced in small amounts by several companies. All of these models are based on blueprints in “Panzer Tracts No.20-2 Paper Panzers”, written in 2002 by American historians Thomas L. Jentz and Hillary Lois Doyle. Other blueprints, wooden models, or even their photographs, did not survive until present day.

Original article available here.

Tuesday 29 October 2013

Vickers' Legacy

The Vickers Mk. E (6-ton) was an excellent tank for its time, and spawned two tanks that will be around for a number of years: the Soviet T-26 and Polish 7TP. I already discussed T-26es being around in the late war, but at least the country producing them was still independent. The 7TP, on the other hand, had no such luxury, and yet, the Americans ran into some in 1944.

An American soldier poses in a twice captured 7TP. More photos here

That's pretty impressive, but not as impressive as the T-26.

T-26 tanks being loaded for transport by the Kuomintang in Shanghai. More photos here.

The photograph is not very unusual by itself, at least until you learn that it was taken in 1949. A full 18 years after the Soviets started building the T-26!

Sunday 27 October 2013

S-41 122 mm Howitzer Project

CAMD RF 38-11369-106:

"Explanatory note for the 122 mm self propelled S-41 howitzer project.

1. Overall view

The 122 mm self-propelled howitzer is designed as a weapon that accompanies infantry and tank units, destroys pillboxes and fortifications with direct or indirect fire, and fights enemy tanks and artillery. 

The main objective of this project is to produce a self propelled gun, with explosive and armour piercing power of the 122 mm shell, combined with mobility of the T-34 tank, by the method of the S-41 122 mm howitzer, which uses shells and ballistics of the model 1938 122 mm howitzer, mount, recoil mechanisms, and many other components from the ZiS-5 tank gun, the breech from the S-3 gun, and the SU-122 SPG, with minor changes.

The gun is composed of a new cannon on a mount from the 76.2 mm ZiS-5 gun. The S-31 85 mm tank gun and S-18 85 mm SPG gun are constructed in the same way. The S-41 122 mm howitzer and S-18 85 mm gun are interchangeable in their installation, and the same parts are used to install both at Uralmash (non-moving armoured components, frame, etc).

Changes to the SU-122 SPG that enable it to use the S-18 gun also enable it to use the S-41 howitzer.

Due to the semi-automatic sliding breech, there is no need for a breech operator.

The ammunition rack placement is the same as on the SU-122. 

The remaining 4 crew members, radio equipment, optics, PPSh, chairs, and other equipment does not change. The ammunition capacity is 50 shells. The mass of the SPG is 30 tons (SU-122 - 30 tons). The SPG with its S-41 howitzer allows for practical rates of fire of 8-10 shots per minute (with aim correction).

The vertical gun range is -5 degrees to +20 degrees (allowing for range of 8.4 kilometers), and the horizontal range is +/- 10 degrees, which allows for sufficient manoeuvrability of fire.

The semi-automatic vertical sliding breech, compared to the M-30 howitzer, results in a howitzer that is easier to service, and allows for installation of a coaxial machinegun or cannon. The roof is raised by 100 mm to aid the loader. The T-10 sight allows direct fire, and the S-3 sight allows indirect fire. 

The self propelled S-41 122 mm howitzer will have the same armoured hull and installation components as the S-18 85 mm self propelled gun. Overall, the S-41 project satisfies the technical-tactical requirements of the Red Army GAU for 122 mm self-propelled howitzers. 

2. Installation of the 122 mm S-41 howitzer in the KV-1S and IS-1 tanks

The design of the 122 mm S-41 howitzer and 85 mm S-31 gun allows for installation in the turrets of the KV-1S and IS-1 tanks using their existing turret rings, with the conversion specifics identical for both guns, as defined by the S-31 project.

KV-1S with 122 mm S-41 howitzer

KV-1S with 85 mm S-31 gun

The installation of a 122 mm howitzer in a tank provides a powerful weapon, capable of destroying pillboxes, fortifications, and combat all types of tanks and self propelled guns of the enemy, his artillery, and personnel. 

This is achieved by the large explosive power of the shell, its weight (23 kg), and muzzle velocity (515 m/s). 

The dimensions of the turret, placement of crew members, fighting compartment layout, turret basket, equipment, communications, optics, radio, seats, hatches, and other components do not change between the S-41 and S-31. 

In this case, the tank can carry 60 shells, 12 of them in the rear compartment of the turret, 10 on the turret basket, and the rest immobile on the fighting compartment floor. 

With a semi-automatic breech and one loader, the practical rate of fire can be as high as 5-6 RPM. 

The mass of the KV-1S with a 122 mm S-41 howitzer will be ____ kg higher than the mass of the KV-1S with the 76.2 mm ZiS-5 gun (43.5 tons), and will be equal to ____ tons.

The specifications of installing the 85 mm gun in the KV-1S and IS-1, and the changes made to the turret and fighting compartment also apply to the 122 mm howitzer (see the TsAKB S-31 project).

In conclusion, the 122 mm howitzer installed in a tank will solve the problem of arming the tank forces with powerful howitzers.

Table of data for the 122 mm S-41 howitzer project


S-41 Project

Gun caliber, mm



Muzzle velocity, m/s



Shell mass, kg



Explosive filler, kg



Propellant density



Maximum pressure, kg/cm^2



Chamber volume, dm^3



Full barrel length


Length of the rifled barrel, m



Number of grooves



Length of grooves



Mass of the propellant with casing



Muzzle energy, t.m.



Mass of the recoil mechanism

1000 kg

Recoil mechanism


Return gear


Recoil length

520 +/- 50 mm

Recoil resistance, tons


Mass of the oscillating part, without armour

1800 kg

Maximum elevation


Minimum depression



Force for vertical aiming

7 kg

Bore axis height



Roof height



Maximum height






Fighting compartment height



Distance from breech to ceiling




Same as SU-122




Practical ROF with fire correction



Ammunition capacity



Same as SU-122

Armouring of the recoil mechanisms

Same as ZiS-5

Overall mass






Table of data for the 122 mm S-41 howitzer as installed in the KV-1S tank



Bore axis height


Maximum height




Same as KV-1S

Height of the fighting compartment


Height from bore axis to ceiling


Turret ring diameter (projected)


Same as KV-1S

Practical rate of fire

5-6 RPM

Size of ammunition rack


Turret armour

Same as KV-1S

Overall mass

Composition of the 122 mm S-41 howitzer
  1. Barrel
  2. Breech (from S-3)
  3. Recoil brake
  4. Return gear (from F-34)
  5. Mount (from ZiS-5)
  6. Firing mechanism (F-34)
  7. Shell catcher
  8. Sight elevation mechanism (S-18)
  9. Elevation mechanism (F-34)
1. Barrel

The barrel monoblock consists of the following main components: barrel, breech, breech ring, buffer tube, and muzzle brake. The overall assembly is similar to the F-34 monoblock, with the difference that instead of two buffer tubes, there is one and a muzzle brake. 

2. Breech

It is a vertical sliding breech of the semi-automatic type, analogous to the F-34 tank gun breech. The use of a sliding breech, compared to the M-30 screw breech, makes the operation of the gun in a turret much more convenient, increases the rate of fire to 8 RPM, and allows for a coaxial machine gun or cannon.

The improved breech removes the necessity of a special loading tray. The sliding breech is much cheaper and simpler to manufacture than a screw breech. 

3. Recoil brake

A spindle type hydraulic brake, same as the one used by the F-34, with the following components replaced: stem, spindle, regulator ring, stem head, stem head nut, and centralizing ring. The replacement of these parts is caused by the increased ballistics and recoil length, and improvement of the robustness of some parts due to the heavier load on the recoil brake.

4. Shell catcher

The shell catcher is a U-shaped bent pipe, filling the role of a recoil guard. A sack is hung up on the pipe to catch shells.

5. Elevation mechanism

The elevation mechanism is from the F-34, with the exception of the flywheel, which is increased in size from 65 mm to 105 mm, with the goal of easing the force applied to rotate it.

6. Return gear

Identical to the F-34.

7. Sight elevation mechanism

The tank version of the mechanism is identical to the ZiS-5 mechanism, the SPG version of the mechanism is identical to the S-18 mechanism.

8. Mount

ZiS-5 mount with several changes.

Chief and Chief Engineer of the NKV TsaKB, Lieutenant-General of the Technical Forces, Grabin

May 27th, 1943"

76 mm AP

For fans of shells, blueprints, and very, very large images, I present blueprint #2-03545: "76 mm armour piercing shell (standard)".

Saturday 26 October 2013

German "Efficiency"

Lots of people attempt to use total casualties of the enemy as some kind of excuse for eliteness of SS divisions. They shouldn't, and this is why.

During the "Winter Magic" operation, between February 25th and March 5th 1943, these 3 German units managed to partisan. And captured a gas mask. In order to do this, they expended 2000 rounds of ammunition and suffered no casualties.

But what is a military operation without trophies and collateral damage? In order to accomplish their lofty goal of killing a single partisan, they also managed to kill 633 civilians and deport 234 (including 54 children). And steal 3.3 tons of grain, and 500 units of livestock. Also they burned down 31 villages, many singular buildings, and one brick factory.

For a partisan and a gas mask.

Friday 25 October 2013

Guns Guns Guns

My search of tank archive materials, unsurprisingly, has led me to accumulate a sizeable amount of firearms related materials are well. Since I hate to see good documents go to waste, I've been somewhat blurring the scope of "tank archives" recently, as well as translating documents for the military surplus thread at the Something Awful forums.

Over only 8 months, this blog has grown from a time waster to win arguments on the internet to a pretty serious resource with thousands of readers per day. Since I don't have nearly as many sources pertaining to firearms or an internet forum full of huge flame wars to generate traffic loyal audience, the other blog might not grow quite as much or update as often, but I hope it will be just as interesting.

Without further ado, Soviet Gun Archives!

Thursday 24 October 2013

Vickers 12 ton in the USSR

According to French intelligence, the Soviets ordered 60 British tanks in 1931.

"Our ambassador in Moscow informs us that the Soviet government just purchased 20 samples each of the 3 main types of tanks available to the British army: a light Vickers tank, 12 tons, a heavy Vickers tank, 35-45 tons, and a Carden-Loyd Mark VI, 1350 kg."

The intel wasn't particularly correct, as there was never a heavy Vickers tank (although the Soviets tried to get Vickers to design one). 12-ton Vickers tanks did exist, and the USSR bought a number of them (14-16, depending on the source). However, unlike the Vickers 6-ton, which birthed the successful Soviet T-26 tank, its fatter cousin was not met with much enthusiasm.

A plan existed to equip these tanks with Maxim machine guns and dig them in as bunkers. However, according to German photos, the Soviets never bothered. The tanks were left to rust out in the open until 1941.

Wednesday 23 October 2013


Remember those super-powerful 85 mm and 107 mm pre-war gun projects? The ones aimed at super-powerful tanks potential enemies of the USSR were allegedly developing? By 1942, the Soviets got tired of waiting for those tanks to show up, and scrapped the whole thing.

CAMD RF 81-12038-50

"By the order of SNK USSR and CC of the Communist Party #P32/116, dated May 14th, 1941, Molotov factory #174, Order of Lenin, produced a prototype of a 107 mm anti-tank gun (using the mount from a 152 mm model 1937 gun).

Trials of the gun and its ammunition were carried out on the Tagil proving grounds, from November 29th, 1941, to January 12th, 1942.

The ballistics requested in the tactical-technical specifications were reached (muzzle velocity of 1020 m/s), but the penetration of 160 mm was not, due to insufficient robustness of the armour piercing shell hull.

According to the conclusions of the Artillery Committee of the Red Army GAU, the 107 mm M-75 anti-tank gun, due to unsatisfactory performance and reliability of receiver and semi-automatic components, insufficient barrel life, and insufficient mount lifetime, the gun failed trials.

As the experience of the war did not confirm the need of this sort of guns in order to combat tanks, I deem it unnecessary to continue development of the M-75 gun or its ammunition in order to get rid of these defects.

As a result of the above, I ask for your permission to terminate work on all work on the 107 mm M-75 gun and analogous work of Stalin factory #92, Order of Lenin, on 85 mm and 107 mm ZiS-23 and ZiS-24 anti-tank guns.

Deputy People's Commissar of Defense of the USSR
General-Colonel of Artillery

April 4th, 1942"

Tuesday 22 October 2013

StuGs for Dummies

In March of 1944, the 311st Assault Gun Brigade, composed of thirty shiny new StuGs (including brand new StuG IVs) and StuHs. The unit was assigned as support for an infantry unit, meant to flank a Soviet counterattack and destroy it. Due to exceptionally poor handling of the tanks by infantry commanders, the entire brigade was lost. When the only thing left of his brigade was its title, Captain von Schoenau wrote some harsh words about how to use StuGs properly.

"In order to avoid further high losses of assault guns, I ask for permission to report my opinions to the corps commanders, which will then be included in instructions to subordinate infantry units.
  1. Any use of assault guns must be prepared and thought through, the area and its approaches scouted out. Considering the current state of the terrain, avoid off-road use to avoid wear of engines and suspensions.
  2. No long marches. The grenadiers should deal with Russian infantry themselves. Assault guns used as pillboxes indicate low morale of the associated infantry unit.
  3. The assault guns must be located where they can reach any point on the front in the shortest amount of time (spider in a web principle). Assault guns are not to be used to guard regimental headquarters.
  4. Assault guns should not be used to support night attacks. The sights do not support night shooting, and create the danger of undershooting. The driver, through his narrow vision slit, cannot see anything at night, and almost certainly will get stuck on terrain. For the same reason, night marches are unacceptable. 
  5. Assault guns are to be used in large groups, with infantry cover. An assault gun is not a tank, and is helpless against enemy infantry.
  6. An assault gun is not a tow truck. Assisting stuck trucks is strictly forbidden. 
  7. Time is needed to prepare the vehicles for battle. The engine has to warm up to 60 degrees, otherwise it will wear out and break.
  8. Due to these reasons, it is important to be economic with your armament, and carefully prepare its order.
The following mistakes were made by the corps when commanding assault guns:
  1. Used them during night operations, in scout groups.
  2. Used them as pillboxes on the front lines.
  3. Gave orders to attack without infantry support.
  4. Night marches for longer than 20 km.
  5. Used them for defence of the command posts.
  6. Attachment of commanders to certain command posts, separating them from repairs, supplies, and command structure for several days."

Sunday 20 October 2013

Soviet Infantry Protection

Popular history treats Soviet infantry as expendables that overwhelm quality with quantity, but examination of actual historical evidence suggests otherwise. Attempts to lengthen the life of the regular soldier (or, in this case, policeman) predate the USSR, beginning with the Russian Empire. "A catalogue of armour invented by Lieutenant-Colonel Chemerzin" describes his inventions, dating back to 1905:

"The armours vary in mass, the lightest are 1.5 pounds, the heaviest are 8 pounds. They are unnoticeable under clothing. Anti-rifle bullet plates weigh 8 pounds. The plates cover the heart, lungs, stomach, sides, as well as the spine and back over the heart and lungs. Each plate is tested for impenetrability in front of the customer."

A little more on trials:
"In the presence of HIS IMPERIAL MAJESTY, on June 11th, 1905, in the city of Orienbaum, a company of machine gunners performed tests. 8 machine guns fired at a plate made from an alloy created by Lieutenant-Colonel Chemerzin, from a distance of 300 paces. It was hit 36 times. The plates were not penetrated, and did not crack. All non-permanent personnel of the infantry school were present."

The Moscow Capital Police, who ordered the armour in the first place, tested it at 15 paces, from unspecified arms. The performance proved exemplary: "[the armour plates] are impenetrable, and do not produce fragments. The first batch is satisfactory."

The St. Petersburg Capital Police report was more thorough: "The results of the trials were as follows: after firing at the front and back plates, one that weighed 4 pounds and 75 zolotniks [a zolotnik is 4.26 grams] and the other 5 pounds 18 zolotniks, composed of steel and wrapped in thin silk fabric, with a Browning bullet, the bullet penetrates the silk, and makes a dent in the plate, but does not penetrate it, and remains in between the silk and steel. No fragments of the bullet fly out."

The Ust-Izhor training proving grounds achieved positive results when testing the plates with "3 line rifles of the infantry type, from 200, 150, 100, 50, and 8 paces."

The archive file further mentions 4791 sets of body armour, 340 shields, and 200 helmets made of this alloy sent to the Warsaw fortress over the period of 3 months.

The invention made a mark on media. The "Rus" newspaper (#69, 1907) wrote: "I saw a miracle yesterday. A young man, thirty years of age, in a military uniform, stood still in a room. A Browning was pointed at him from half a pace, a frightening Browning, aimed right for the chest, for the heart. The young man waited, smiling. A shot struck, the bullet bounced off.
"See," said the military man. "I barely felt anything.""

"Novoye Vremya" wrote on February 28th, 1908: "The invincible armour and new breastplates are wonderful inventions of our century, and surpass the knight's armour of the past. The scale layers remain the same, but the alloy is different. It is the inventor's secret. A. A. Chemerzin only explained the main idea behind his discovery. A. A. Chemerzin is a Lieutenant-Colonel of engineering forces. He finished a degree in mathematics, then an engineering school. He taught mathematics, while studying chemistry, and a series of experiments led him to exploration of nickel-chromed steel. The alloy was created under high temperature and pressure. Precious metals like platinum, silver, iridium, vanadium, and many others were added to the mix. This led to a very ductile and strong metal, that is 3.5 times tougher than steel. As a result, at three paces, the Mauser bullet could not penetrate a half-millimeter plate. Armour and breastplates were made that were impenetrable for revolver and rifle bullets, which deformed without giving off fragments. The danger of concussions and ricochets was solved.
The armour is expensive, but life is costs more. Putting on the 5 pound armour that covers the front and back, I did not consider it heavy. It is entirely unnoticeable underneath a suit. 7000 breastplates, helmets, and shields were sent to the army in the Far East, but sadly, too late..."

Indeed, the invention did not come cheap. 1500-1900 rubles would buy you a standard set of armour. 5000-8000 could buy you a custom-made set, tailored to your body. Chemerzin also offered the armouring of a carriage (20,000 rubles) and a car's engine compartment (15,000).

In 1916, Chemerzin's armour was tested for pilots. While it performed admirably, a cheaper armour was chosen, manufactured at the Petrograd mechanical and metalworking factories.

I don't have anything about the interbellum period, but the question of protecting infantry was explored during the Winter War.

CAMD RF 81-12040-69

"In 1939, NKV NII-13 manufactured trial batches of steel SN-39 (150 units) breastplates and SNSh-39 (100 units ) breastplate-shields, which were then tested in combat (on Karelia). 

As is stated in our previous report for 1940 (report T-06-77), the breastplate received good reviews from the commanders of the 7th army, but the issue of increasing the strength of the armour in order to ensure bullet protection in close combat was raised. 

To resolve this issue, we have created a new (thickened) breastplate, SN-40A. According to the orders from GAU KA, a decision was made to mass produce the SN-40A, with the following goals in mind:
  1. Manufacture 100-150 SN-40A breastplates, providing protection from model 1908 bullets fired from a rifle or machine gun from 150 meters at 0 degrees and from any distance at 30 degrees.
  2. Manufacture the breastplates in three sizes. Previously, breastplates were produces in one size (small).
  3. Explore the requirements for production of the breastplates and develop blueprints for equipment to mass produce the breastplates.
  4. Conduct proving ground and battlefield trials to determine if the breastplates can be accepted by the Red Army.
The aforementioned mass production of the SN-40A is the topic of this report."

SN stands for Stalnoy Nagrudnik (steel breastplate). 

CAMD RF 81-12040-69

"The manufacturing of the SN-40A was done at the "Industria" factory in Lysva. The breastplates were produced in 3 sizes, and in two thicknesses and weights. The blueprints of the the breastplate are shown in figure 2."

Trials of the SN-40A were performed in the fall of 1941. The results were unsatisfactory. At 5.2 mm (one batch was 4.2 mm), the breastplates were too heavy. Even the air force did not want to use them. One would not immediately expect a heavy breastplate to matter in an airplane, but it does. "Uniform of the Russian Air Force 1935-1955" writes "The medical corps frequently equipped pilots with army type steel helmets. For example, in 1943, elements of the 4th Air Army made it mandatory for Il-2 and Pe-2 gunners to wear "a metallic helmet and special breast shields". However, in practice, when breaking away from a steep dive, the rear gunner was subjected to unacceptable forces, which lowered his capacity of defending the plane from enemy fighters." However, the specific breastplate in question was almost certainly not the SN-40A, but its successor, the SN-42.

The SN-42 was developed in the spring of 1942 and tested in August of the same year by airborne troops. It was composed of 36 SGN type steel, and was 2 mm thick. 500 units were manufactured, and sent to be tested in the army.

Overall view of the breastplate

Breastplate used as a shield

Breastplate used as a shield while prone

The results were as follows:

CAMD RF 81-12040-109

"In 1942, according to the orders from the GAU of the Red Army, the Scientific-Investigative Institute #13 of the USSR NKV, developed a steel breastplate 3.3 kg in mass, 2 mm thick, that protects the main organs of the human body against German submachineguns at all distances, and rifles and machineguns at 300 meters. 
According to GOKO order #2160ss from August 8th, 1942, the steel breastplates were sent to the army, and received positive reviews. The reviews mention the following:
  1. The steel breastplates provide reliable protection from German submachineguns, as well as fragments of mines and hand grenades.
  2. The maneuverability of soldiers with breastplates is almost unimpaired.
  3. Aside from providing protection for the soldier, the breastplate also increases the soldier's morale when performing his duties.
The technical documentation on the steel breastplate was accepted by the GAU of the Red Army on August 7th, 1942, after which the breastplate was mass produced at factory #700 (city of Lysva). At this time, 85,000 breastplates have been produced, distributed as follows:
  1. South-Western Front: 5,000
  2. Stalingrad Front: 3,000
  3. Leningrad Front: 1,000
  4. Volhov Front: 1,000
  5. Don Front: 5,000
70,000 units remain at the warehouse. "

The benefits of the SN-42 breastplate are outlined in more detail in a letter from the deputy commander of the artillery of the 68th Army to the head of the GAU KA, Major-General Hohlov.

CAMD RF 81-12040-109

"In November of 1942, the 57th army received 5000 steel breastplates to test. After the army established the reliability of the breastplates by shooting them from 100 meters with rifles, they issued a small amount (500 units) on a trial basis.
The breastplates were met with distrust, but commanders requested the breastplates in maximum available numbers after testing them in battle. All breastplates available in the warehouses were given out. In battles for Stalingrad, they were exhaustively tested.
Comments by unit commanders and soldiers say that the breastplate, in addition to the steel helmet, is a good and reliable method of protection from bayonets, bullets, and shrapnel.
It is also necessary to point out the morale value of the breastplate. Soldiers equipped with the breastplates that have experienced their reliability go into battle calmly and assuredly.
The artillery supply units are constantly receiving orders for additional breastplates. All these factors combined lead me to believe that the breastplates live up to expectations and are a worthwhile investment.
Please issue 15000 units to the 68th army."

Popular history dictates that only specially formed assault groups were equipped with SN-42 breastplates, but you may already be suspecting that it was not so. The breastplates were not meant for any one kind of soldier, as their instruction memorandum reveals:

CAMD RF 81-12040-69

"A memo on the use of SN-42 steel breastplates
  1. The steel breastplate safeguards the chest and stomach of the soldier in combat from 1) bullets of a German submachinegun at any distance 2) bullets of rifles and machineguns at 300 meters 3) fragments of mines and grenades.
  2. The steel breastplate, thanks to its construction, does not stifle the soldier's movement while walking, running, or crawling.
  3. The breastplate weighs 3.3 kg. To maintain the soldier's endurance and maneuverability, the soldier must be lightened at the cost of his backpack load.
  4. The breastplate can be used by:
    1. scouts, out on a mission.
    2. sappers, while out scouting, making breaches in barbed wire, defusing explosives under enemy fire, etc.
    3. infantry teams during scouting by combat.
    4. submachinegunners, sneaking through the enemy lines, riding as tank infantry, and laying in ambush.
    5. assault teams, attacking a pillbox.
    6. soldiers fighting in city streets.
    7. communications personnel, checking and fixing telephone lines under enemy fire.
    8. any other situation where the commander deems that the breastplates can be usefully applied.
  5. The breastplate can be used in 3 ways.
    1. The breastplate is attached using straps and covers the chest and stomach during movement.
    2. When crawling, the breastplate can be used as a shield.
    3. When removed, the breastplate can be used to cover other parts of the body (right side, left side, head).
  6. The breastplate consists of:
    1. a hull, with the upper and lower plates.
    2. soft lining, attached to the hull with a snap pin.
    3. belts for attaching the breastplate: one on the waist and two on the shoulder
  7. The breastplates are made in three sizes. The breastplate is 2 mm thick.
The breastplates are handed out by the Front Commanders, and are to be used by those armies where they can be usefully applied. Army and Front Commanders should send their feedback on using the breastplates and suggestions to the General Staff of the Red Army, and send a copy to the GAU of the Red Army.

November 11th, 1942"

At the same time as the SN-42, the SShN-42 (steel shield-breastplate) was developed. 

CAMD RF 81-12040-69

The SShN-42 was thicker than the SN-42, at 4.9 mm. Only 25 SShN-42s were produced. The design passed trials, but their subsequent fate is unknown. Is is probable that they joined their regular breastplate cousins in the 5th Army for testing. 

CAMD RF 81-12040-69

In 1942, NII-48 developed its own batch of a spin on breastplates: bulletproof vests. The armour was composed of four plates: two in the front, and two in the back. The vest tied in the front with two bows, like a lifejacket. 

From minutes #215 section 40 of the Sverdlovsk Regional Committee, on August 30th, 1942 (TsDOOSO 4-18-15): 

"On the manufacturing of a trial batch of personal methods of protection for riflemen and machinegunners

The Regional Committee of the All-Union Communist Party of Bolsheviks approves of the initiative of the NII-48 in developing a design of personal armour protection and its mass production, and decrees that:
  1. The director of the Uralmash factory comrade Muzrukov and director of NII-48 comrade Zavyalov must ensure the production of 200 units of personal armour and 50 units for personal armour for Maxim machinegunners by September 20th, 1942.
  2. The VIZ director, comrade Radkevich, must provide to the Uralmash factory 3 tons of rolled 30 HGS steel for production of trial personal armour sets.
  3. NII-48 director comrade Zavyalov is urged to manufacture a trial batch of armour sets and send them to the Red Army for practical tests. In the event that the tests pass and the armour is accepted for mass production, send the proposal to the Regional Committee.
  4.  The General Secretary of the Sverdlovsk All-Union Communist Party of Bolsheviks must provide all necessary resources to factories in order to produce the personal amour sets for riflemen and machinegunners.
Regional committee secretary Andrianov"

500 vests were produced in total. They all were sent to the 5th Army, but did not saw very limited combat. It did, however, see enough that the Germans captured one unit.

"The picture was attached to a message from an intelligence officer in the headquarters of the German 35th Panzer division, informing the command of the 9th Army Corps that the enemy is using new defensive gear on October 2nd, 1942 called an "armoured vest", drawn based on an inspection of the unit captured during a battle."

The picture on the right is also of interest to us.

"Another picture from an intelligence officer in the 35th Panzer division, composed based on the statements of POWs from the 1158th regiment, which revealed that the regiment assault group used this second model of defensive gear on October 2nd, 1942, obtained with the purpose of evaluating its usefulness in battle. Based on the sketch, it was probably a prototype of the SN-42."

Based on reports from the front lines, NII-48 gave their bulleproof vest another try.

CAMD RF 81-12040-69

The change is pretty self-evident: two more plates were added to the front to protect more of the soldier's body. 

CAMD RF 81-12040-109

Here is another breastplate design, this one is a little different. Instead of one lower plate, there are three. The upper plate is composed of two pieces. The back also has a full shirt, not just straps. Its index was PZ-ZiF-20. As its name suggests, it was produced at the Frunze factory (#7). It did not perform as well as the SN-42, but was produced in large numbers anyway, as the army needed all the breastplates it could get. These breastplates were first issued in 1943. 

While the SN-42 was, no doubt, the best Soviet breastplate of the war, work did not stop with it. The financial plan for the second quarter of 1945 of the 6th Department of the Tank Directorate of GBTU KA (CAMD RF 38-11355-2756) mentions the following: 

"An experimental batch of bulletproof vests is being manufactured by the NKTP and NKLP factories. The vests are a new type of protection for Red Army soldiers. The contract is still being processed. The approximate cost is 500,000 rubles."

It is hard to judge how much 500,000 rubles is worth in today's money, but it is no small cost. For example, in 1941, developing the SPG-212 (more commonly known as Object 212) cost only 100,000 rubles.