Oreshnik Against Zelensky's Bunker [i]

Hypersonic missile against underground bunker

This article is about the damaging effects of ammunition with a particular analysis of what the Oreshnik warhead can do to a target. The whole subject of hypersonic impact on the ground is highly technical and often relies on empirical and simulation research. It can be the subject of many scientific research projects and theses. This article attempts to explain a very complex problem to non-technical readers and describe the characteristics of the hypersonic warhead and how it may affect a highly classified underground facility such as a top command post.

To better understand the overall problem, readers are advised to read the previous two articles discussing the first use of Oreshnik and attacks on underground objects:

Introduction to ammunition damaging effects

Before diving into this particular problem, two things need to be clarified: The effectiveness of the damaging effect on the target and combat effectiveness. The damaging effect is described as the ability of ammunition to damage or destroy a target with a direct impact, or if it produces sufficient damage to incapacitate the target if it is activated within a predetermined damaging distance from the target. The combat effectiveness of a munition depends not only on the effectiveness of the ammunition on or near a target but also on the accuracy of the ammunition delivery, the reliability of all its elements (the fuse in particular), the ability to withstand the enemy’s defensive actions, etc.

Most ammunition acts on a target either by the kinetic energy of the munition itself or by the chemical energy of the explosive contained in the munition.

There is also ammunition that does not damage targets but serves as a countermeasure to protect or reduce the damage from the enemy’s ammunition.

In general, the following is the effect of the munition:

• fragmentation,

• penetration,

• cumulative - shaped charges,

• blast - high explosive & volumetric explosion,

• incendiary,

• nuclear, and

• unified by type of action.

The degree of damage is the minimum time during which a particular target cannot function as intended. According to Prof. Balagansky, three main degrees of damage are used, depending on the time the object remains nonfunctioning:

A – time sufficient to solve the operation’s objectives;

B – time adequate to address the daily objectives;

C – when the object is suppressed for the duration of a battle.

For different targets and combat missions, the times mentioned in the previous paragraph corresponding to various degrees of damage may vary significantly, and, in some cases, additional degrees of damage are introduced (for example, for armored vehicles or hardened structures, an additional D degree may be used). Sometimes, the A degree is associated with the destruction of the target, B with its partial failure, and C with temporary suppression. The degree of damage is established and is determined by the duration of disruption of the combat function for military equipment and structures and by the minimum required hospitalization and treatment time for the personnel.

The A-degree will be elaborated in detail.

All ammunition can be divided into ammunition with an impact or contact effect that can only damage a target after a direct hit (shaped charges, armor-piercing, concrete-piercing) and those with a remote effect that can damage a target when exploded at some distance from it (fragmentation, high-explosive ammunition). In the case of the Oreshnik, a combination of sheer kinetic velocity and penetration causes damage due to both the impact and the shock waves induced by the magnitude of the explosion.

The conditional damage law G(m) for contact ammunition is a term that defines destructive effects on single small targets. According to work by Prof. Wentzel ("Introduction to Operations Research"), that is understood to be the probability of damaging a target that is hit by "m" projectiles. The conditional damage law simultaneously describes both the destructive power and the degree of vulnerability of the target of the projectile attack.

The average number of hits required to destroy a target designated as "ω" is a convenient numerical characteristic of the conditional damage law:

When a hypervelocity projectile perforates a target, what happens is that both the target and the projectile undergo tremendous stress, including fragmentation, spallation, melting, mixed flow, vaporization, and ionization. In the immediate impact zone, the target is completely pulverized. In this process, an “ejecta cloud” of fragments is formed that moves from the impact face of the target and expands in the direction opposite to the projectile motion, as well as a “debris cloud” of fragments that propagate and expand downrange from the rear face of the target. The researchers must analyze and understand the formation and evolution of the ejecta and debris clouds, including shape, fragment sizes, velocities, etc., to determine the extent of the target damages, damage radius, and energy absorption. For military planners, it is essential to see if the applied munition will serve its purpose and destroy the designated target. Practically, the knowledge of the size and the three-dimensional velocities of the individual fragments in the debris cloud can lead to the determination of their group kinetic energy, momentum, and the energy absorbed and dissipated by the target. Knowing these parameters can help the design of protection measures. Propagation of the shock waves from the zone of impact and their interactions with nearby structures and the particle field can provide an improved understanding of high-velocity impact phenomena.¹

What does this mean for the existing high-value objects and structures in Ukraine? While theoretical research is important, it is critical to know whether an underground bunker that houses Zelensky, other VIPs, and the command center can withstand the impact of a hypervelocity munition.

When a ballistic missile like Oreshnik, with multiple re-entry vehicles, hits a target, it can cause cumulative damage, which is the phenomenon where the projectiles “help each other” to damage or destroy the target. One warhead may be sufficient to cause damage to some degree but not necessarily destruction; but the target can be destroyed by the combined action of two or more warheads.

Remote ammunition can affect a target with a direct hit but also when it explodes some distance from the target. The target is damaged by the products of the explosion and the shock wave (high-explosive ammunition) or by high-velocity fragments (fragmentation ammunition). If an Oreshnik warhead doesn't have an explosive charge, the sheer momentum and transfer of (kinetic) energy will cause an effect similar to an explosion-induced shockwave. To do that, the warhead must hit within the damage zone of the targeted object.

In this case, the main characteristic that determines the effectiveness is the coordinate law of damage G(x,y,z). It is a functional relationship between the probability of the target damage and the coordinates of the explosion point of the ammunition relative to the target. The simplest type of coordinate law is for high-explosive ammunition, the effect of which is estimated by the target destruction radius Rd. Hence, for high-explosive ammunition, the coordinate law is expressed as a simple stepwise dependence on the distance to the target R. If the projectile explodes at a distance R ≤ Rd from the target, then G(R) = 1, and at R > Rd, G(R) = 0. The area of space around the target, inside which G(R) = 1, is called the area of unconditional target damage. The boundaries of this area are lines or surfaces equidistant to the target contours². The zone of unconditional target damage by the blast/shock wave action is shown in the following picture:

Coordinate laws of damage vary depending on the nature of the target, ammunition capacity, and other conditions. For a deeply buried command bunker/post such as the ChZ 417 object in Kiev, that will be depth, wall composition, surrounding media composition, Oreshnik speed, angle of impact, payload, and weight, to name just a few. When considering these laws, three different areas can be identified around the center of the target. One of these areas (γd) is characterized by the fact that a round of ammunition bursting at any point within it always leads to the destruction of the target. This area is called a reliable damage area. This is followed by an area (γi) where it does not necessarily result in the target being damaged. This is referred to as the area of unreliable damage. The area (γs) in which ammunition does not damage the target at all is called the safe area.³⁴

Areas surrounding the center of the target. Source: From Fendrikov and Yakovlev [3].

Consider a single (small) target that provides certain functions (see illustration B in the picture below). This target might be a purposely built underground bunker used by field commanders (brigade level or higher). An efficiency indicator, W=P(A), is often used to estimate potential damage to the structure, where A is the damage inflicted on the target.

A group target consists of several single targets united by a common mission. When targeting it, it is necessary to damage the group as a whole and thus prevent it from continuing its mission.

An underground object located under one or more buildings (see illustration A in the picture below) can be considered a group target consisting of several single targets beneath each building. Examples are basements (or underground garages converted to command posts), warehouses, and workshops united by a common mission. When firing, it is necessary to damage the group as a whole and thus prevent it from fulfilling its mission. In Ukraine, there are underground locations beneath government buildings or factories.

An area target consists of a set of objects distributed within a specific area in an obscure way (see illustration C). A good example of an area target is the underground post ChZ-417 (see below). This complex consists of primary and secondary entrance shafts, tertiary entrance from the subway line, ventilation shafts, accommodation space, operational space, auxiliary units, etc. that can be connected with interlocking tunnels but can be isolated in the case of emergency. Typical for an area target is that it is not the individual objects that are targeted, even if they can be targeted independently, but the entire area. As an efficiency indicator, the expected value of the portion of the damaging area M=M[U] is used, where U = Sd/St (the ratio of the damaged area to the whole target area).

Typical Soviet bunkers (from D. Yurkov, Sovetskie Sekretni Bunkeri, Gorodskaya Sprcialnaya Fortifikaciya 1930-1960s)

Project ChZ-417

The well-known underground bunker that can house Zelensky, his team, the air defense and army command structures, together with foreign advisors is the underground premises located directly under the government building complex in the center of Kiev. This Soviet-era complex is known as Project ChZ-417.

This is also known as the "bunker on Arsenalnaya.” These are the underground premises located next to the Arsenalnaya subway station. This station holds the world record for depth - it is buried 105.5 m deep.

Arsenalnaya subway station [7].

Scheme of lowering the intermediate vestibule of the Arsenalnaya station [7].

In Kiev’s Natalka Park, they have begun reconstruction of a concrete caisson, which is called the "Stalin’s metro". The concrete structure, was created before the Second World War for the construction of tunnels under the Dnieper [8]. Similar concrete profiles are used for Arsenalnaya and other subways stations.

In the early 1950s, the implementation of the ChZ-417 project began in Kiev - the construction of a complex of underground shelters for the air defense command, as well as for the leadership of the Ukrainian SSR.

At a depth of 93 m, there were to be protected premises for the work of the organs of the Central Committee of the Communist Party of Ukraine, the Supreme Council of the Ukrainian SSR and the Council of Ministers of the Ukrainian SSR. According to the project, the shafts were to withstand a direct hit from a high-explosive bomb weighing 2,500 kg.⁵ To a greater extent, the facility was conceived as a place where the leadership could survive a nuclear attack.

The "Bunker on Arsenalnaya" is located directly under the complex of government buildings of the Ukrainian capital. However, to what extent the project was implemented and what condition the facility is in today is not known for sure, at least to the public.

ChZ-417 has two blocks. Each is an 8.5-meter-diameter tunnel about 100 meters long. The tunnel is divided into two or three floors, where utility rooms are arranged. Block B is technical and contains the facility's life support systems. Block A is the operational premises block.

The following photos are from an unfinished tunnel close to the Arsenalnaya station and can be used as an example of how the Soviets built them. To some degree, the construction of the ChZ-417 can be considered very similar to this unfinished tunnel:

https://www.urbextour.com/ru/podzemelya-kieva/komandnyj-bunker-metro/

The available data for Block B can give an idea of ​​the total length of the facility. The pumping station and the filtration (filter-fan) chamber take up 30 meters of the block's length, and 17 meters are for drainage pumping (no matter how much of the waterproofing the underground premises, water will still come in and it will have to be pumped out into the city sewer). Another 15 meters are for the electrical distribution board, 17 meters are for the diesel power plant, and finally, 5 meters are for the fuel storage. In total, considering the areas for stairs and passages, the length will be from 80 to 100 meters.

Bloc B (support systems) for ChZ-417

Diesel generator power plant. The size of the bunker and the power consumption require at least 3 emergency generators (2-on, 1-off) for emergency power supply. The power supply during regular times comes from the grid, but that can be easily disabled.

In addition to the two shaft entrances, there is a passage from the bunker to the Svyatoshinsko-Brovarskaya metro line. It comes to the tunnel between picket marks 68 and 69. This is approximately 300-400 meters from the center of the Khreshchatyk station towards Arsenalnaya.

Besides the ChZ-417 completion, there were other plans for extension and access. In the Soviet Union, underground structures were often considered secret, so the work was carried out in three shifts: shafts and mines were built, and the earth was taken out of the city at night in trucks covered with tarpaulins. When the main work on the development of additions and the construction of a special block was completed, the Soviet Union collapsed, and the secret metro construction was stopped and forgotten. Even the workers who sometimes go there to change light bulbs do not know what they are servicing. A handful of masked structures on the surface in the form of an ordinary boiler room and an exit to the Khreshchatyk-Arsenalnaya section were welded shut with bars - that's all that remains from the construction of yet another bunker in case of a nuclear war.

Unfinished underground tunnel - remnants from the Soviet times in Kiev, close to the Arsenalnaya subway station (https://www.urbextour.com/ru/podzemelya-kieva/komandnyj-bunker-metro/).

Steel section used in the “lining” of the underground tunnels. D. Yurkov, Sovetskie Sekretni Bunkeri, Gorodskaya Sprcialnaya Fortifikaciya 1930-1960s

Similar design: Inside the ChZ-417. It is a concrete and steel structure with multiple levels, rooms and auxiliary spaces for equipment. It is located about 93 m underground and connected to Khreshchatyk-Arsenalnaya subway segment.

During the Soviet years, many underground structures were built in Kiev and the vicinity. For example, the underground control center of the Kiev metro was never completed. Local diggers also know about an abandoned underground air defense command post built at a relatively shallow depth of 18 meters before WWII.

In addition, the Kiеv Military District command built several facilities at a depth of about 35 meters in the post-war period.

It is no secret that some of these structures have fallen into a rather deplorable state over the years of independence, but there are more than enough places in Kiev to hide Zelensky safely. Some industrial enterprises also have underground structures—for example, the Azovstal plant in Mariupol or bunkers under the Yuzhnoe plant in Dnepropetrovsk.

Lviv also has (had) its underground bunkers. During the Soviet years, the city housed the headquarters of the Carpathian Military District, which, of course, had classified protected facilities in case of a military situation. The "Apricot" facility, an underground communications bunker of the Carpathian Military District consisting of more than 50 rooms, has long been looted and is desolate.

Approximately the same fate befell other similar objects in the territory of the Lviv region. In addition, maintaining such systems in working order is a costly luxury, and independent Ukraine was chronically short of money. As for the party leadership of the Lviv region of the Soviet era, their status did not allow them luxurious underground apartments.

Oreshnik incoming? No worries! Thank you! ChZ-417

Let’s assume that ChZ-417 will be targeted with one Oreshnik missile containing six independent re-entry hypersonic vehicles moving at 10 Mach. Oreshnik may also have each of these independent warheads fitted with six smaller warheads (“6x6” configuration), or it may use just one. At the time of writing this article, these details are not known.

As previously mentioned, ChZ-417 may be treated as an area target because multiple entrances are located at a considerable distance. Two warheads may be designated to eliminate the entrances. Public information is scarce, but let's assume at least two possible surface entrances are disguised within the government complexes. These entrances are reinforced to survive the direct impact of at least 2500 kg bomb (the reason for this is that they were designed in the 50s, and consideration was taken for the heaviest ordinary bomb. At today's use, that would be the FAB-3000 bomb. The following illustration is an example and may not represent the existing entrance of the ChZ-417.

One typical example a concealed bunker entrance. It may be one of the CH-417 entrances.

So far, nobody outside of Russia's strictly military and political circles has seen an Oreshnik hypersonic projectile, so there is wide speculation.

Most theoretical analyses of the hypersonic penetration of rigid projectiles into thick concrete are based on laboratory-scale small-caliber projectile tests. Due to the size effect, evaluating their applicability for larger caliber projectiles is difficult. Ogive-nose projectiles are often used for hypersonic weapons rather than solid long-rod projectiles, limiting the availability of high-speed penetration test results.

As scientific analysis and corresponding mathematics are outside the scope of this article, only some basic information will be presented. The bibliography and further reading section list references for those interested.

According to source [3], after the penetration tests, the concrete targets were carefully cut along the penetration boreholes, presenting the sectional views of five targets. The tunnel diameter gradually decreased from the tunnel entrance to the end of the tunnel to equal the diameter of the projectile shank, indicating that the high-speed movement of the projectile/target interface at the initial stage of penetration caused the concrete to expand radially and independently move outward a certain distance based on the surface velocity of the cavity before stopping.⁶

A tiny (few millimeters thick) projectile moving at hypersonic speed (but much less than the Oreshnik warhead) penetration into the thick concrete target was tested in the lab with numerical simulation. The order of magnitude for the hypersonic warhead is at least 100x higher. (From “Hypervelocity Impact Cratering on Semi-Infinite Concrete Targets of Projectiles”) [3].

The experiment and photos shown above are used in this article to illustrate the penetration. However, during the Oreshnik hypersonic warhead penetration, this is magnified by 100x or more. The Russian source said that the surface temperature of the warhead is 4000 C, and to withstand this temperature, a special alloy, combination of alloys or ceramic based material is developed. The composition is top secret. It is known that Tantalum-Hafnium carbide or Hafnium carbonitride has a melting point of almost 4000 C but these materials are used only as an example. If the warhead can resist 4000 C without melting, maybe is something else added. Density is another unknown and can be easily higher than 16 g/cc. Depleted uranium would be the densest material available but it was definitely not used in Oreshnik. It may also be some alloy based on Wolfram (Tungsten) Vanadium base. In any case, it is a great unknown for now. One thing is sure: with a 4000-degree body temperature, which is moving 10 Mach (3.43 km/s), and with approximately 200 kg weight, the concrete around the shaft will partially evaporate, and the warhead will penetrate due to momentum and energy to a depth of 80-100 m. The following illustration presents what may happen with an almost perpendicular impact on the surface of the reinforced concrete above the shaft.

Shear stress and distribution on the tunnel exposed to the shock wave (cylindrical waves). The impact of the shock wave on any structure may break it. With this, the shaft will be rendered useless for a long time. The shock waves can also create a spall effect.

The Oreshnik warhead can break through the 6 m diameter shaft and permanently disable or destroy it, so it can’t be used without a lengthy repair, if even possible. Directionally focused energy will create local extreme shockwaves (red lines with arrows) that can break any concrete structure, such as a staircase or elevator shaft.

Six independent warheads (MARV - Maneuverable Reentry Vehicles) may be used to hit entrances (one per entrance), while the remaining four can be used to strike after each other in the underground tunnels simultaneously.

The impact of just one Oreshnik missile on the decision-making center deep into the ground can cause significant damage and render it useless for a prolonged time. The effect is not only the physical destruction but also the disabling of auxiliary functions such as air filtration and power supply. Command centers can't function without this stuff, so even damage to these components can impair the functionality of the whole Command and Control system. D. Yurkov, Sovetskie Sekretni Bunkeri, Gorodskaya Sprcialnaya Fortifikaciya 1930-1960s

Let's now discuss the possibility that even one Oreshnik cannot reach the depth of the bunker. If it penetrates only 60 or 70 meters, it can still create a shockwave that may create a local micro-earthquake that may damage the bunker structure.

The previous article, “Oreshnik Enters the Chat,” explained how seismic action develops, so it will not be repeated here. For illustration, seismic waves are shown in the following:

The underground impact creates a micro-earthquake. Oscillations of the soil under the shockwave can hit the obstacle of the different densities, creating the effect that may break the concrete structure and create spall. This micro-scale earthquake can break the bunker structure, causing issues such as water flooding through the cracks, unbalancing, and damage to equipment such as filtration systems or drainage systems, etc. Source: Miropolsky, F.P., Sarkisian, R.S., Vishniakov, O.L. et al. (1996). Aircraft Warheads and Their Investigation.

The effect of the shockwave that Oreshnik can create includes overpressure, thermal effects, energized projectiles (fragments, debris, and missiles), ground shock, and caterings. The peak particle velocity (PPV) is the most representative parameter for describing the ground motion and tunnel response. Blast stress waves have limited duration, high vibration frequencies, and short wavelengths, which affect tunnels in the form of cylindrical waves. This can also create a spall effect.

During the hypersonic penetration, compressed products make a sharp impact on the adjacent layers of soil, compressing them and creating a shock wave in the ground. The warhead movement displaces the surrounding soil, driving it in radial directions. The initial pressure at the front of the generated shock wave depends on the properties of the soil.

There are several works addressing the tunnel behavior under the shock wave stress where simulation methods are applied taking into consideration specific boundaries. To some extent, the kinetic impact shock waves can be similar to those addressed in the works (referenced at the end).

Shear stress and distribution on the tunnel exposed to the shock wave. Dynamic damage and response characteristics of the tunnel by FEM modeling and field trials; Journal of Vibroengineering, May 2023, 25(3)

The attack

As Ukrainian attacks with the US supply weapons on Russian territory continue, President Putin repeatedly warned that Russia may strike decision-making centers. The action of the Ukrainian service in the assassination of the top Russian military commanders will likely further contribute to retaliatory measures.

Decision-making bunker ChZ-417 not only houses the Ukrainian leadership during the attacks on Kiev but also has a nerve center for the AD and communication on the highest levels that also includes foreign advisors. Let's be clear - ATACMS mission planning, selection of targets, intelligence, and programming are in the hands of NATO/US. Ukrainians in the field have an auxiliary role - loading missile containers and launching. This bunker in the center of Kiev is likely the top decision-making center.

What Russia can achieve with this is the elimination of the military leadership, maybe even political leadership, as well as key NATO personnel in Ukraine. If the center is only damaged or rendered unusable for the time being, it will require relocation to some less-protected locations that are easier to destroy.

How might Russia execute the attack? Similar to the Dnipro attack, it will likely be conducted at night to reduce the presence of civilians. Russia may also inform Ukraine about the attack simply because Ukraine has no means of intercepting missiles.

Disabling shafts leaves one or two auxiliary entrances through the Kyiv subway system, which is a bigger problem than the shafts. The exact location is not publicly known, but Russians understand where they are. Arsenalnaya station is one of the deepest in the world. It was built with the same circular concrete-steel structure, and itself has a safety factor higher than the one used in ordinary railroad tunnels. Hitting the subway station full of civilians is not an option, but the entrance may be hit to block access.

If Russia wants to destroy the complex without leaving any potential functionality, considerations may be given of disabling the two nearest stations, Khreshchatyk and Dnipro. These stations are not so deep. Dnipro station is interesting because it is almost by the river, so a hit may be sufficient to cause flooding, and the water will flood the Arsenalnaya, which is at the lower level. This will probably destroy the auxiliary access to ChZ-417 but also can cause significant civilian casualties, so it is highly likely not an option for the Russians.

Conclusion

The Russian leadership has considered multiple options regarding this attack, and it is up to President Putin to give the order. Tools are available. He already said that Oreshnik would not be used against small targets, but the Ukrainian national command center is definitely not a small target. Several Oreshnik missiles increase the probability of disabling/destroying the target. Will this happen? Time will tell.

President Zelensky is a useful tool for NATO and the EU. His actions resulted in enormous Ukrainian casualties (with 8-10:1 compared with Russian). He is dismantling the Ukrainian military and that works for Russia. The question is if he is eliminated, who will replace him? Some want peace and some are psychopaths and want to drag the world into WWIII. If Russia can somehow get those psychos that will save a lot of lives down the road.

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[i] Edited by Piquet (EditPiquet@gmail.com)

References

1. I.V. Balagansky: Damaging Effects of Weapons and Ammunition, Willey

2. .M. Mansoor, J.D. Trolinger, J. George International Journal of Impact Engineering Volume 172, February 2023, 104421)

3. Hypervelocity Impact Cratering on Semi-Infinite Concrete Targets of Projectiles, Cheng Shang, Wenjin Liu, Siyuan Ren and Renrong Long State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China

4. High-speed penetration of ogive-nose projectiles into thick concrete targets: Tests and a projectile nose evolution model, Xu Li,  Yan Liu,  Junbo Yan,  Zhenqing Shi, Hongfu Wang, Yingliang Xu, Fenglei Huang 

5. Dynamic Response of Curved Tunnels under Vertical Incidence of Transversal SV Waves; Huiling Zhao, Yuheng Ma, Xupeng Yao

6. Numerical study on tunnel damage subject to blast-induced shock wave in jointed rock masses, X.F. Deng, J.B. Zhu, S.G. Chen, Z.Y. Zhao, Y.X. Zhou, J. Zhao

7. Analysis of the dynamic response and damage characteristic for the tunnel under near-field blasts and far-field earthquakes, Hao Luo, Ming Tao, Zhixian Hong, Gongliang Xiang, Chengqing Wu

8. Kievski Metropoliten, Golovko G.V., Kolomiec N.S.

9. D. Yurkov, Sovetskie Sekretni Bunkeri, Gorodskaya Sprcialnaya Fortifikaciya 1930-1960s (Советские Секретные бункеры. Городская специальная фортификация 1930-1960-х годов (Юрков Дмитрий)

10. Dynamic damage and response characteristics of the tunnel by FEM modeling and field trials; Journal of Vibroengineering, May 2023, 25(3)

11. Design of Underground Structures (Cui, Z.-D., Zhang, Z.-L., Yuan, L., Zhan, Z.-X.

12. Miropolsky, F.P., Sarkisian, R.S., Vishniakov, O.L. et al. (1996). Aircraft Warheads

    and Their Investigation. Moscow: Zhukovsky Academyetc.)

13. https://cfts.org.ua/news/2021/04/30/v_kieve_tonnel_stalinskogo_metro_prevratyat_v_restoran_foto_64650

14. https://www.urbextour.com/ru/podzemelya-kieva/komandnyj-bunker-metro/

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1. M.M. Mansoor, J.D. Trolinger, J. George International Journal of Impact Engineering Volume 172, February 2023, 104421

2. Balagansky, I.V.: Damaging Effects of Weapons and Ammunition, Willey

3. Balagansky I.V. : Damaging Effects of Weapons and Ammunition, Willey

4. Fendrikov, N.M. and Yakovlev, V.I. (1971). Methods of Calculation of Combat Efficiency of Armament. Moscow: Voyenizdat [in Russian].

5. 2500 kg was likely related to the German WWII SC 2500. Current Russian bomb, by weight is FAB-3000.

6. High-speed penetration of ogive-nose projectiles into thick concrete targets: Tests and a projectile nose evolution model, Xu Li, Yan Liu, Junbo Yan, Zhenqing Shi, Hongfu Wang, Yingliang Xu, Fenglei Huang