Topic B-4-46: Homogeneous armor under heavy fire
128mm PAK 44
A brief clarification regarding the archival document, which is provided in full below. This report, top secret for its time (1946), reveals the nuances of the resistance of domestic and German armor to shells up to and including 152 mm in caliber. The work was conducted at the Central Order of Lenin Research Institute-48, better known as the "Armor Institute." The original declassified report is stored in the Russian State Archive of Economics. The document's contents are difficult to understand and require a certain level of preparation from the reader. The style and presentation of the material have been preserved in full. The editor has provided clarifications where possible.
Study of the interaction between projectile and armor and further study of the tactical properties of armor under artillery fire of up to 128 mm caliber
The work had the main goal:
1) obtaining data on the anti-projectile resistance of homogeneous armor against large-caliber armor-piercing anti-tank projectiles artillery, both domestic and German;
2) drawing up graphs of the tactical properties of armor necessary for calculating armor during design tanks and other armored objects.
Experimental firing, necessary to obtain data on the tactical properties of the armor, was carried out on homogeneous plates with a thickness of 90 to 230 mm, with armor-piercing projectiles from 88 to 152 mm caliber inclusive at different angles.
A total of 29 armor plates were tested at the testing ground, of which 10 large-sized experimental plates were made from a 12-ton sheet ingot and 19 small-sized plates (cards) cut from sheets made from 23-ton ingots.
In addition to the data on the experimental plates, this work also used materials from the Kubinka test site (in Kubinka near Moscow, editor's note) on the shelling of two experimental hulls of the "260" object and captured materials from the Hillersleben test site obtained in 1946 on the shell-proof resistance of German armor when shelled by German shells up to 170 mm in caliber.
The study found that for both large-caliber armor-piercing projectiles and smaller-caliber projectiles, their penetration ability also decreases sharply at high impact angles, which must be taken into account when designing armor protection for targets. Tests showed that reducing the hardness from 3,4-3,64 d to 3,6-3,8 d (referring to the Brinell hardness, editor's note) does not significantly affect the projectile resistance of thick armor, whether fired at normal or oblique angles. The reduction in armor's projectile resistance only becomes significant when the armor is softened to a hardness greater than 3,8 d. Softening the armor slightly improves the damage profile, but this is not the primary factor determining the resulting damage profile.
Based on the processing of the obtained materials, tactical diagrams of the projectile resistance of homogeneous armor under fire from domestic and German armor-piercing projectiles of calibers from 80 to 152 mm inclusive are provided, which are necessary for calculating the armor protection of objects from projectiles of these calibers.
Introduction
A characteristic feature of modern tank and anti-tank artillery is its exceptionally increased power, due both to larger calibers and higher muzzle velocities. A clear example of this is German artillery at the end of the war, which by that time possessed tank and anti-tank guns with a maximum caliber of up to 128 mm and maximum muzzle velocities of 1000 m/s. However, even such calibers and velocities are not the ultimate. There is evidence that, by the end of the war, Germany was intensively developing more advanced tank anti-tank artillery with a maximum caliber of up to 170 mm and a maximum muzzle velocity of 1400–1500 m/s.
Domestic anti-tank and tank artillery has undergone and is undergoing approximately the same changes.
Thus, as a result of the increase in initial velocities and calibers of shells, modern anti-tank and tank artillery has exceptionally high penetrating power.
The latter circumstance is clearly illustrated by the data in the table and the graph displaying the change in muzzle energy of guns of various calibers of German artillery depending on the initial velocity of the projectiles.
Changes in muzzle energy of German anti-tank and tank artillery depending on the initial velocity of the projectile (based on captured data from the Hillersleben firing range).
The data presented demonstrates that increasing caliber and, especially, muzzle velocity are significant factors in enhancing the weapon's power. For example, increasing muzzle velocity from 800 m/s to 1000 m/s, or by 25%, increases the projectile's muzzle energy by 56%. A 50% increase in velocity (V = 1200 m/s) more than doubles the muzzle energy. This clearly illustrates the difficulty in developing reliable protection against modern large-caliber tank and anti-tank artillery.
In light of this, the great practical significance of data on the tactical properties of armor under fire from modern anti-tank weapons is clear, in particular for the purpose of accumulating materials for the possibility of subsequently determining the probable tactical properties of armor against advanced artillery.
In recent years, the institute had conducted a number of comprehensive studies on the tactical properties of homogeneous armor under fire from domestic and German artillery up to and including 85mm and 105mm calibers, respectively. However, its tactical properties against larger-caliber artillery had remained completely unexplored. Accordingly, in 1946, the institute was tasked with studying the behavior of homogeneous armor under fire from large-caliber tank and anti-tank artillery. This would provide insight into the performance of large-caliber armor-piercing shells and identify ways to provide more effective protection against shells of these calibers.
This report presents data on the tactical performance of domestic homogeneous armor under fire from both domestic and German large-caliber artillery, based on all available materials. In addition to this data, this report also includes interesting captured data from the Hillersleben Proving Ground on the armor-piercing performance of German shells of various calibers. Given that all of the data presented on the tactical performance of homogeneous armor is of considerable value as a reference for calculating the armor protection of designed objects, it is presented primarily graphically for ease of calculation.
Hillersleben training ground
The presented materials, although essentially covering all existing large calibers of domestic tank artillery, due to the small volume of tests carried out, must be further refined as data on firing accumulates, which is one of the objectives of the Institute's subsequent work in the field of studying the tactical properties of armor.
Testing tools
Projectile tests of the homogeneous armor were conducted at the KNIMAP naval artillery range, which has the appropriate facilities for testing armor with large-caliber projectiles. The plates were fired from 100, 122, and 152 mm caliber guns using armor-piercing projectiles in inert filler.
Brief characteristics of guns and armor-piercing shells and their ballistic data are given in the table.
Main characteristics of 100, 122 and 152 mm armor-piercing shells.
In addition to testing with domestic shells of the specified caliber, tests were also carried out with German armor-piercing shells of 88 and 105 mm caliber against homogeneous armor plates of large thicknesses (200-230 mm), which had not previously been tested with these shells.
152mm Canet gun. Photo from 1905.
122 mm A-19 gun
100-mm naval gun model 1940 (B-34)
Test objects
The tactical properties of the armor were determined using experimental homogeneous armor plates of medium hardness, manufactured at the Magnitogorsk Iron and Steel Works (MMK) using bulk technology, i.e., from metal smelted in the main open-hearth furnace and cast into sheet molds weighing 12 tons. Larger plates, rolled to the appropriate thickness, were subjected to heat treatment, consisting of water quenching and subsequent high-temperature tempering to a hardness of 3,4–3,6 d.
In addition to the medium-hardness plates used to measure tactical characteristics, homogeneous plates of the same melt and technology, processed to a hardness of 3,7–3,9 d, were also tested.
Due to the limited number of manufactured and tested plates of this hardness, the obtained test data on these plates could not be used for tactical properties and served only for comparative purposes.
In addition to the data obtained during testing of experimental armor plates manufactured by the Magnitogorsk Iron and Steel Works, this work used the results of testing control and experimental plates produced by the Izhora Plant, made from base metal cast in sheet molds of greater weight (23 tons).
Based on fracture characteristics, all armor plates produced by the MKK and Izhora Plant were of average quality for homogeneous armor and average hardness in general production, and were therefore considered acceptable. However, the 160 mm thick plates produced by the Izhora Plant, and especially the control plates, exhibited poor fracture quality, which will be discussed in more detail below.
test data
The results of field tests of experimental and control armor plates of different hardness and thickness allow us to note significant variations in the resistance of individual control plates with a thickness of 160 mm, which were observed when the armor was fired at with sharp-nosed armor-piercing projectiles.
This circumstance is likely a consequence not only of the uneven quality of the plates, but should be explained to a greater extent by the non-standard qualities of domestic sharp-nosed projectiles. Their non-standard quality is apparently caused by the way the projectile's nose reacts to the localizer at different points during its penetration of the plate; i.e., in one case, the projectile functions for a longer period as a sharp-nosed projectile, while in another, it functions as a blunt-nosed projectile.
It should also be noted that a similar phenomenon, to an even greater extent, was previously observed during large-scale armor testing with domestic 65mm caliber pointed-nosed shells. Experience has shown that more consistent results under fire are obtained when testing with blunt-nosed armor-piercing shells, which means that using this type of shell in some testing situations for a more objective assessment of armor resistance under fire may prove more appropriate.
Without considering here the influence of differences in the qualitative and quantitative characteristics of armor fracture on the nature of damage during through-penetration, which should be addressed in a separate, dedicated study, we will limit ourselves to brief general comments on the nature of damage to homogeneous plates observed during shelling with large-caliber armor-piercing projectiles. First of all, it should be noted that all plates manufactured by both the Magnitogorsk Combine and the Izhora Plant exhibited, to varying degrees, defects that were revealed during field testing. Flaking is characteristic of MMK plates, while slate formation and delamination are characteristic of Izhora Plant plates. Flockens (German: Flocken, literally "flakes") are internal cracks (defects) in steel forgings and rolled products. Slate fracture is a layered (tree-like) fracture that manifests itself as small splits that barely extend deeper into the metal. Editor's note.
In terms of damage patterns during through-penetration by large-caliber projectiles, no other damage patterns were observed on homogeneous armor other than spalling. Variations in spall size were observed across the plates, likely due to differences in fracture quality. No clear correlation was found between the relative spall size (expressed in projectile calibers) and plate hardness, projectile caliber, or firing angle, with the exception of armor thickness. In the latter case, a clear correlation was established: spall size increased with increasing armor thickness. This was particularly evident on plates 150 mm thick and above, where spall size, even for experimental armor plates, in some cases exceeded 3 calibers. The lack of data on spalling of 230 mm armor plates is explained by the insufficient velocity of shells from domestic guns of 100, 122 and 152 mm calibers, as a result of which through penetration was not achieved for these thicknesses.
The deterioration in armor damage patterns with increasing armor thickness is likely due to a decrease in metal compression during hot machining. This suggests that, to improve the quality of thicker armor, it may be necessary to modify existing hot machining technology to ensure the required deformation, resulting in a more satisfactory armor damage pattern in the event of through-and-through penetrations.
Methods of processing experimental data
Usually in practice, when studying the tactical properties of armor against large-caliber projectiles, one has to be satisfied with experimental data obtained on a relatively limited number of plates of certain basic thicknesses at test angles no higher than 600, as a result of which the obtained experimental data usually require special processing in order to obtain the necessary additional data on untested thicknesses or angles.
In previous years' research on the tactical properties of armor, the Institute used the following graphical method for processing the results of direct experiments. Based on experimental data, projectile resistance curves were constructed for each armor type, caliber, and projectile type in the velocity-armor thickness coordinates when fired at angles of 0°.0, 300, 450 and 600, which were subsequently extrapolated toward higher and lower speeds. Moreover, when extrapolating the curve toward lower speeds, it was assumed that U = 0 and b = 0; when extrapolating the curve toward higher speeds, it was assumed that the projectile resistance curve retained its regularity.
Based on the obtained auxiliary graphs, tactical diagrams of projectile resistance in the coordinates of velocity and firing angle were subsequently constructed for each type of armor and projectile caliber.
Basically, the indicated method of processing experimental data, which, as experience has shown, gives results that are sufficiently reliable for practical purposes, was adopted in the present work.
It should be noted, however, that the specified method makes it possible to determine the projectile resistance of armor only against projectiles of the caliber for which there is specific experimental data, but this method cannot be used to calculate the armor resistance against projectiles of a different caliber, even in the case of its similarity, which is one of the disadvantages of this method.
In this regard, it's necessary to say a few words about the work of engineer G. I. Kapyrin and engineer V. V. Larchenko, in which they proposed a method for calculating the projectile resistance of armor against projectiles of any caliber, provided the projectiles are similar. Without dwelling on this method, which the authors thoroughly outline in their work, it's necessary to briefly touch on some of its characteristic features.
Using some provisions established by Cand. of Technical Sciences Aibinder in the analysis of the armor penetration process based on the theory of similarity, the authors, as a result of processing the experimental data of the field tests of armor with German armor-piercing projectiles of caliber 50, 75, 88 and 105 mm, came to the conclusion that for projectiles of similar design, the speed characterizing the anti-projectile resistance of armor depends only on the ratio of two coefficients Cb to Cq, where: Cb = b/d (b is the armor thickness and d is the caliber of the projectile) - the so-called relative thickness of the armor and Cq = q/d3 (q is the weight of the projectile and d is its caliber) - the so-called relative weight of the projectile.
Based on the established pattern, a series of graphs were proposed, constructed in the coordinates: speed - Cb/Cq and Cв/Cq - angle of fire, which were recommended for practical use in determining the projectile resistance of homogeneous armor of medium and high hardness against German artillery shells of any caliber at an initial velocity of up to 1200 m/sec.
It should be noted, however, that the proposed method for calculating projectile resistance could not be used in this work, since when processing experimental data on domestic projectiles of 122 and 152 mm caliber using this method, such a scatter of experimental points was discovered (apparently due to the lack of similarity between these projectiles) that it was not possible to establish any specific pattern at all.
Thus, as indicated above, the previous graphical method of processing experimental data was used in this work.
For the tactical diagrams, the results obtained during the firing of experimental homogeneous armor plates of medium hardness, which were tested at various angles, were mainly used.
In this case, due to the very limited number of slabs tested, the data from firing all slabs were used if they met the requirements of the old technical specifications, which allowed spalling of up to 4 calibers.
This circumstance, in our opinion, may be acceptable when processing data for the tactical properties of armor, as no effect of spall size on the speed of antitank penetration (which is typically used to calculate armor) has been established and, apparently, may have a very minor impact on another, less important characteristic—the speed of the antitank penetration. However, despite this, when processing data for drafting technical specifications for firing at control plates, it is necessary, in addition to armor resistance, to examine the nature of damage during overpenetration, which is necessarily regulated in the technical specifications.
PTP – rear armor strength limit, PSP – armor penetration limit. Editor's note.
The test data from the control plates, tested primarily in the normal direction, served only to confirm and slightly adjust the test data for the tactical properties.
The question of the effect of reducing the hardness of the armor on the tactical properties also could not yet be finally resolved, since the tests conducted on low-hardness armor were insufficient for this.
Tactical diagrams of armor projectile resistance
As a result of processing the available experimental data on the resistance of medium-hard armor, auxiliary graphs were obtained for different calibers of domestic shells, which are shown in the figures.
It should be noted that in constructing these graphs, significant difficulties were encountered due to the scatter of the few experimental data that were available for these calibers.
In addition to these auxiliary graphs, which make it possible to determine the resistance for any thickness, but for certain firing angles (specifically not higher than 600), graphs of the type proposed by engineer Kapyrin and engineer Larchenko were also constructed, based on the fact that for the resistance curves constructed in the coordinates "firing angle - armor thickness", for any initial projectile velocity, the angle of attack from the normal of 90° is the zero point.
Based on these auxiliary graphs, the main tactical diagrams of the armor's projectile resistance against 100, 122, and 152 mm projectiles were constructed.
Thus, the final diagrams reflect the corrected tactical properties of the armor after mutually linking and harmonizing data for adjacent thicknesses and firing angles (smoothing the curves of the auxiliary graphs). For this reason, the armor's projectile resistance as shown in these diagrams may differ from that determined directly at the firing range by firing at specific armor plates.
From the data presented, with the exception of the thickness of 200 mm, which is clearly excluded from consideration, it is clear that, although there are individual cases of significant discrepancies between the data in the diagrams and the experimental data (which are planned to be verified in the future), nevertheless, for the majority of cases, there is a fairly good agreement between them.
Thus, it can be assumed that the presented graphic materials on the projectile resistance of homogeneous armor within the real velocities of domestic guns of calibers 100–152 mm reflect the tactical properties of homogeneous armor under various test conditions with sufficient accuracy for practice and therefore, for these projectile velocities, can be recommended as the main material when calculating armor protection against projectiles of these calibers.
The influence of hardness on the projectile resistance of homogeneous armor
In domestic armor production, homogeneous tank armor with a Brinell hardness of 3,3-3,6 has found widespread use only for thicknesses no greater than 120 mm. For thicker homogeneous armor, achieving a hardness within these limits is, for a number of specific reasons, challenging. Therefore, the current hardness limit for armor of these thicknesses is tentatively set at 3,5-3,8.
Due to the very limited amount of experimental data on field tests of homogeneous tank armor with a hardness below 3,6, in this work we are, unfortunately, unable to provide sufficiently detailed data on the influence of the hardness of homogeneous armor on the tactical characteristics of the latter.
A noticeable reduction in the projectile resistance of homogeneous armor 150 mm thick or greater is observed only when the hardness drops below 3,8 at angles close to the normal. When fired at higher angles, the projectile resistance of such armor will be either equal to or only slightly lower than that of armor of medium hardness.
As for the armor's projectile resistance at projectile velocities higher than those actually tested, i.e. in the range from 800 to 1000 m/sec, the latter are more approximate data that require immediate experimental clarification, since in this case they were obtained purely by calculation.
Anti-projectile resistance of homogeneous armor plates with a thickness of 160 mm
Given the widespread use of 160mm-thick homogeneous armor as the primary armor for new heavy tanks, it is appropriate to examine in more detail the results of field tests of armor plates of this thickness produced by the Izhora Plant. These plates are distinguished by the use of heavier ingots (23 tons), a characteristic feature.
The table below shows the projectile resistance data for homogeneous plates of different hardness.
Projectile resistance of 160 mm thick homogeneous plates from the Izhora plant when fired at normal angles by 122 mm projectiles, drawing 209519
From the data provided it is evident that, with significant variations in the resistance of individual slabs, the average values of the PTP and PSP of homogeneous slabs with a hardness of 3,45-3,65 d and 3,65-3,80 d are approximately the same.
The influence of the hardness of homogeneous armor on the nature of damage during through penetration in this case, although it shows a certain tendency to improve the nature of damage with a decrease in the hardness of the armor, however, the presence of individual plates with good spalling quality with higher hardness and, conversely, substandard spalling on plates with lower hardness indicate that the decisive factor determining the nature of damage to the armor is not the hardness, but the quality of the armor in terms of fracture.
Tactical properties of domestic homogeneous armor under German artillery fire
In addition to studying the tactical properties of homogeneous armor against domestic armor-piercing projectiles, in this work, tests were carried out on homogeneous armor plates with a thickness of 150-230 mm with German armor-piercing projectiles of caliber 88 and 105 mm to clarify the previously obtained diagrams of the tactical properties of armor against these calibers.
The obtained data were processed using a similar methodology to the above data from tests with domestic shells.
Despite the inevitable adjustment of individual experimental data when processing experimental material, the projectile resistance determined from tactical diagrams agrees with the actual data with sufficient accuracy for practice.
The influence of hardness on the projectile resistance of homogeneous armor when fired at by German 88 mm caliber armor-piercing shells is presented in the table.
The influence of hardness on the resistance of homogeneous armor against German armor-piercing shells.
The table shows that a noticeable effect of hardness on the projectile resistance of homogeneous armor is observed only when the armor hardness is significantly reduced—below 3,6 d. In this case, armor resistance is significantly reduced both when fired at a normal angle and at an angle of 300.
88mm PAK 43
The projectile resistance of domestic homogeneous armor under fire from German 128mm caliber armor-piercing shells, unfortunately, could not be studied in sufficient detail in 1946 due to the absence of a German gun of this caliber at the Leningrad proving grounds.
However, using captured materials from the Hillersleben proving ground, which will be discussed in detail below, data from the Kubinka proving ground on testing the experimental object "260" with German 128-mm shells and available data on the shelling of domestic armor with German shells of smaller calibers, tactical diagrams of the projectile resistance of domestic homogeneous armor against shells of this caliber were obtained by calculation.
260 object
Calculations of armor's shell resistance against German shells of this caliber, although conducted in two slightly different ways, were both based on the principle of similarity of German shells. This assumption, as will be shown below, is acceptable for rough calculations of shell resistance, at least up to shell velocities of 800 m/s.
In one case, the projectile resistance calculation was based on the conversion of the "K" coefficient, calculated using the Jacob-de-Marr formula for the German 105mm shell, to the 128mm shell. In the other case, the German armor's resistance curve against 128mm armor-piercing shells was adjusted for the domestic armor by comparing the resistance curves of domestic and German armor under fire from the same German shells and establishing a general pattern in the curves' patterns. It should be noted that the calculated projectile resistance values for the through-penetration limit, when compared in both cases, showed fairly good agreement.
128mm PAK 44
It should also be noted that the verification of the obtained calculated resistance diagrams with the actual data from the Cuban test site for testing the “260” object with German shells of this caliber at thicknesses of 100 and 150 mm also showed good agreement between the calculated and actual data, which is illustrated by the diagram, which shows the calculated curves for armor thicknesses of 100 and 150 mm and the actual data on the resistance of armor of these thicknesses when fired from a German 128 mm caliber gun.
Tactical properties of German homogeneous armor
Until now, the materials available to the Institute for the Effects of German Tank Artillery on domestic tank armor were mainly limited to a caliber no higher than 105 mm, which, however, is not the limit for German anti-tank artillery, the actual calibers of which by the end of the war reached 128 mm and higher.
In light of these circumstances, the information obtained by the Institute in 1946 on captured materials from the Hillersleben test site (Germany) turned out to be very interesting.
Before examining this data, it should be noted that the materials from the Hillersleben proving ground, obtained from the Artillery Committee of the Main Artillery Directorate of the Armed Forces, are presented exclusively in the form of graphic material, reflecting only the projectile resistance of German armor under fire from their own anti-tank artillery, without any explanatory text, on the basis of which it would be possible to establish some information about the properties of German armor, etc.
However, despite the lack of this data, indirectly, by comparing and analyzing captured and domestic data on the same calibers of shells and based on the results of numerous studies of German armor conducted during the Second Patriotic War, it was possible to roughly establish not only some of the qualitative characteristics of German armor, but also to some extent evaluate the reliability of captured German data.
The projectile resistance (according to PSP) of German homogeneous armor at various testing angles with German armor-piercing projectiles of different calibers, according to data from the Hillersleben proving ground, is presented in the diagrams.
From the data provided, it is clear, first of all, that they cover the entire range of calibers of German tank and anti-tank artillery.
The high muzzle velocities of German shells, which for some calibers significantly exceed the maximum velocities of German guns known to us (such as 75 and 88 mm), lead us to assume that these data are mainly the results of firing experimental guns with high muzzle velocities, which, apparently, the Germans intensively developed in the last stage of the war (which can be assumed from the large volume of tests carried out).
When analyzing the armor penetration curves of German armor, one crucial factor must first be noted: armor penetration increases consistently with increasing thickness only up to a specific projectile velocity. This pattern then reverses, and at very high velocities, further increases in projectile velocity do not increase penetrating power. It also turns out that the "critical" projectile velocity at which this phenomenon is observed depends quite significantly on the projectile caliber; as projectile caliber increases, the "critical" velocity shifts toward higher velocities. Specifically, for a 75mm projectile at a 30° firing angle, the "critical" velocity is approximately 1300 m/sec, and for 88mm projectiles, it is approximately 1400 m/sec.
It should be noted that a similar phenomenon is also observed at large firing angles, at approximately the same or slightly higher speeds.
The sharp drop in armor-piercing shell penetration at high velocities is likely due solely to shell fracture at high muzzle velocities, which even highly durable armor-piercing shells like the German ones experience. Therefore, one might expect that for less durable armor-piercing shells, this phenomenon would occur at even lower velocities. However, we were unable to detect this phenomenon due to the lack of guns with high muzzle velocities at which this phenomenon could be clearly observed.
The cited data from the Hillersleben Proving Grounds suggest that increasing the muzzle velocity of an armor-piercing projectile is only practical up to a specific velocity, dependent on the projectile type and its caliber. For example, for projectiles with an armor-piercing tip, the muzzle velocity limit for a 75mm caliber projectile is likely to be no higher than 1200 m/s, and for an 88mm caliber projectile, no higher than 1300 m/s.
Comparing the data on the projectile resistance of German armor based on the Hillersleben Proving Grounds and available data on testing domestic armor with German shells of the same caliber, it can be seen that, in terms of the through-penetration limit, German projectile-resistant armor at small b/d ratios (b is the armor thickness and d is the shell caliber) is slightly more resistant than domestic armor; at a b/d ratio of approximately one, it is equally resistant to domestic armor; and at a b/d ratio significantly greater than one, German armor is inferior to domestic medium-hardness armor. The observed difference in the resistance of German and domestic armor at various ratios is apparently due to the reduced hardness of German homogeneous armor compared to domestic armor.
Thus, the German data from the Hillersleben Proving Ground reflects the resistance of German homogeneous armor, which is lower in hardness than domestic homogeneous armor. The likelihood of this assumption is supported to a certain extent by the relatively good agreement between domestic testing data on low-hardness armor (3,7–3,9 d) and the German data.
The comparative penetrating action of German and domestic shells of similar calibers on domestic armor is presented in the diagram.
The diagram shows the high penetrating effectiveness of German 105mm armor-piercing shells compared to domestic 100mm blunt-nosed armor-piercing shells, especially at relatively shallow firing angles. At higher firing angles, the opposite is true, with the German shells' penetrating effectiveness being inferior to their domestic counterparts.
It should be noted that a similar phenomenon was previously discovered by the author also for domestic and German shells of smaller caliber (85 and 88 mm), which, apparently, is characteristic of these types of shells.
In conclusion of the review of the Hillersleben test site data, it is necessary to briefly discuss the results of processing the German data using the method proposed by engineer Kapyrin and engineer Larchenko.
The choice of German data for this purpose is quite obvious, as these materials cover all calibers of German tank artillery, with a fairly extensive amount of data for each caliber. The Hillersleben Proving Ground data for the case of oblique fire are presented in the diagram.
Looking at this diagram, one can see that the distribution of points for each specific shell caliber is quite consistent, distinct from other calibers. It's impossible to tell, especially at shell velocities above 800 m/s, where the different nature of the resistance change even for shells of similar calibers (75 and 88 mm) is undeniably obvious. As for lower velocities, although a greater concentration of points is observed for almost all German shell calibers (except 50 mm), the distribution of the points does not at all indicate a strict similarity between German shells even at lower velocities.
In light of the above, the possibility of practical application of this method, especially for calculating the resistance of armor against projectiles with a high initial velocity (above 800 m/sec), may prove to be appropriate only in the case of an approximate calculation against the same calibers of projectiles for which there is no direct test data.
In conclusion, it must be said that, despite the shortcomings noted above, the proposed calculation method must be recognized as a very valuable attempt to establish the general dependencies of projectile resistance on the main parameters of the projectile and armor, and further research in the direction of its improvement must be recognized as highly advisable.
Conclusions on the work performed
Based on the materials presented and reviewed in this report, the following main conclusions can be drawn:
1) The armor-piercing action of German and domestic large-caliber shells (88–152 mm) against homogeneous armor of medium hardness is highly effective only when fired at normal or at small impact angles. Under these test conditions, armor-piercing shells, at impact velocities of approximately 1000 m/s, are capable of penetrating armor more than twice the thickness of the shell's caliber.
2) At large angles of impact of the projectile with the armor, the penetrating effectiveness of armor-piercing domestic and especially German projectiles decreases sharply, which can be used when designing armor protection for structures.
3) The superior armor-piercing effectiveness of German armor-piercing shells compared to domestic ones is observed at low impact angles and relatively small angles of attack. When fired at high angles, the armor-piercing effectiveness of German shells is inferior to that of domestic shells. This again confirms similar conclusions made in 1945 regarding the different penetrating effects of German and domestic shells at high impact angles.
4) Reducing the hardness of homogeneous armor 150 mm thick and above from 3,4–3,6 d to 3,6–3,8 d causes virtually no noticeable reduction in projectile resistance against domestic and German shells, either when fired at normal or at angles. When armor hardness decreases below 3,8 d and when fired at angles close to normal, a noticeable reduction in projectile resistance of homogeneous armor is observed, approximately 10% of the resistance of armor with a hardness of up to 3,6. Regarding shell impacts at high angles, there is reason to expect that reducing the hardness of homogeneous armor to these limits will not significantly affect the projectile resistance of armor of these thicknesses, which requires more detailed experimental confirmation.
Conclusion
As a result of the work carried out in 1946, the tactical characteristics of homogeneous armor under fire from domestic and German anti-tank artillery were studied, on the basis of which tactical diagrams of the projectile resistance of domestic homogeneous armor with a hardness of up to 3,6 d against projectiles from 88 to 152 mm caliber were determined, which are recommended for use as the main material for armor resistance against projectiles of this caliber when calculating the armor protection of structures.
The presented materials, although essentially covering the majority of large-caliber domestic and German artillery, nevertheless require supplementation and clarification, especially depending on the change in armor hardness, which is one of the tasks of the Institute’s subsequent work in the field of further study of the tactical properties of armor.
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