rexford

Zitadelle, Thanks for the great post. Russian penetration range figures, like those of other nations, should always be looked at with suspicion at first examination. The Russians sometimes compared the face-hardened penetration of their guns to homogeneous armor on German tanks and calculated a range which was not correct. Real firing test data has been found from Russian sources, the question is whether the Ferdinand figures are calculated or firing trial, and if calculated whether they used face-hardened penetration data. Many sources say the Ferdinand and Elefant carried homogeneous armor. At Kursk, a Ferdinand/Elefant was hit many times at close to medium range by 76.2mm rounds with only one non-damaging penetration.

There are reports and I've seen the accompanying pictures where Nashorns knocked out Stalin tanks at 2000m and greater ranges with penetrations of the turret front or mantlet. The turret front was 100mm rounded, the mantlet 110mm (or 100mm) and rounded, and the high hardness armor could lose some resistance due to brittleness. The IS-2 hull front could be 90mm rolled armor at 30 degrees, which could be penetrated by the Tiger II and Nashorn at a good range.

The following site has some info which indicates that Russian tungsten core ammo contained mercury compounds which could vaporize after penetration, injuring or killing crew members: http://www.geocities.com/Pentagon/Base/1852/57mm.html

rgriest1 on the Yahoo! Tankers site explained the different slope multipliers on the basis of APDS cores hitting the armor directly, whereas HVAP has a lightweight carrier which impedes the angled penetration and boosts the slope multiplier. [ March 30, 2004, 03:30 PM: Message edited by: rexford ]

The Russian Battlefield discussions indicate that the initial IS-1 tanks had a narrow mantlet cause it was designed for the 85mm gun. A vision slit close to the gun barrel would still allow acceptable viewing cause the 85mm is fairly narrow, was just the right length and did not have a muzzle brake. Whan the IS-1 tanks got 122mm guns, the same mantlet was used and it caused vision problems for the gunner (longer, thicker gun barrel with a giant muzzle brake on the end, compared to the 85mm gun). http://www.battlefield.ru/is2_1.html shows a picture of a production IS-1 tank with 85mm gun, and indicates when the last 85mm armed IS-1 tank was produced (January 1944). Only a small number of 85mm armed IS tanks were produced. While Mr. Zaloga states that 85mm armed IS tanks did not see combat, the Russian Battlefield info suggests otherwise. Perhaps the design team might wish to indicate what info swayed their decision (when did Zaloga's book statement come out?). That problem was cured by installing the wider mantlet where the gunner vision slit was moved further from the 122mm gun. There were IS-1 tanks with narrow mantlets and 30 degree from vertical driver plates. The Russian Battlefield discussions mention that the 85mm gun was found to be a failure against Panthers and Tigers and was replaced with the 122mm. [ March 30, 2004, 02:18 PM: Message edited by: rexford ]

U.S. and British data give differing views on the slope effects of APDS and HVAP, and the main projectile difference causing the differences would probably be nose shape. Were the nose shapes on the British 17 pdr APDS and U.S. 76mm HVAP rounds similar or different? Both rounds had 3.9 pound cores with 38.1mm diameter. The following is a comparison of slope multipliers that convert angled hits to an equivalent thickness of vertical armor: 76mm HVAP 1.35 at 30 degrees from vertical 2.26 at 45 degrees 4.24 at 60 degrees 17 pdr APDS 1.23 at 30 degrees from vertical 1.82 at 45 degrees 3.51 at 60 degrees For British 37mm APDS (an experimental round), the penetration vs angle curve results in the following slope multipliers: 37mm APDS 1.39 at 30 degrees from vertical 2.01 at 45 degrees 4.01 at 60 degrees For both sizes of British APDS, the slope effects at 45 and 60 degrees are lower than U.S. 76mm HVAP. This suggests that the 45 and 60 degree slope effects may have been a function of nose shape, but a comparison needs to be done. At Isigny, 17 pdr APDS made it through the Panther glacis with an impact angle of 57 degrees from vertical due to ground tilt. Applying the British slope multiplier for 17 pdr APDS to 82mm at 57 degrees results in about 2.9 x 82mm or 238mm vertical, while the 76mm HVAP slope effect would result in 82mm x 3.6 or 295mm vertical. Based on British data, 17 pdr APDS could penetrate 238mm vertical at about 900 meters and could not penetrate 295mm vertical at any range. With regard to 17 pdr APDS against Panther, it might be useful to halve or third the APDS that is given to British tanks and TD's with 17 pdr guns due to the following factors: 1. rounds were erratic in behavior and often failed to hit known targets at known ranges during firing trials 2. rounds were erratic in behavior and might fail against a given plate one time in a test and then succeed at a much lower velocity 3. Panther glacis quality is not 0.85 for all tanks but really was quite random.

The following presents the latest research findings regarding the shatter failure of U.S. 76mm APCBC against heavy German armor (80mm and thicker): SHATTER GAP FAILURE OF U.S. 3” CHEVROLET APCBC Firing trials and combat reports from WW II suggest that the Chevrolet 3” APCBC round was susceptible to shatter gap failure, where hits which should have penetrated resulted in defeats. The following summarizes all of the research conducted by this writer on the subject of U.S. 76mm APCBC shatter gap and refines past estimates. 1. Report in Faint Praise book that U.S. 76mm penetrated front of Tiger at 50 yards in France but failed at further ranges 2. U.S. firing trials against captured Panthers in France (First U.S. Army, July 1944) where penetration range against Panther mantlet is limited to 200 yards (183m) 3. U.S. Navy firing tests against American 3.8” and 3” plate result in two distinct velocities for 50% success separated by a wide band of failure velocities with extensive projectile damage Analysis of the above information results in the following shatter gap characteristics: 3.82” at 20 deg, U.S. Navy, 1.124 shatter gap penetration ratio 3.84” at 30 deg, U.S. Navy, 1.125 3.00” at 20 deg, U.S. Navy, none (no shatter gap exhibited) 3.00” at 30 deg, U.S. Navy, 1.229 3.00” at 40 deg, U.S. Navy, 1.193 102mm at 10 deg, Faint Praise, 1.210 100mm cast at 0 deg, U.S. First Army, 1.323 100mm cast at 10 deg, U.S. First Army, 1.284 100mm cast at 20 deg, U.S. First Army, 1.160 Notes: 1. The Shatter Gap Penetration Ratio is the ratio of the higher penetration figure for 50% success divided by the lower limit (based on computed effective armor resistance), where the figures in between would result in a high failure probability due to projectile shatter 2. The First Army tests against the Panther mantlet did not indicate or suggest an impact angle, so three possible angles are analyzed where the lower angles may be more likely Applying the above results to the Tiger effective armor resistances results in the following ranges for potential shatter gap failure by Chevrolet 76mm APCBC (50% penetration probability at listed ranges, zero percentage in between and normal penetration probabilities outside the range): 102mm plate hit at 10 degrees, 46m to 1050m 102mm plate hit at 20 degrees, 100m to 750m 102mm plate hit at 30 degrees, 25m 84.5mm side armor resistance at 20 degrees, no shatter gap possibility 84.5mm side armor resistance at 30 degrees, 0m to 1100m 84.5mm side armor resistance at 40 degrees, no shatter gap possibility, no 50% intact penetration limit For the Panther mantlet, the upper and lower penetration ranges appear to occur at 183mm and 1500m. Research by Miles Krogfus has found that the Chevrolet M62 3” round was susceptible to a variety of problems due to a relatively rapid decrease in hardness from nose to main body, which could lead to bulging out of the projectile shoulder after impact. There were two other manufacturers of U.S. 76mm APCBC and the other makers used a slower variation than Chevrolet for the hardness from nose to main body.

The U.S. 76mm APCBC round was compared to the 85mm APBC during a Russian firing trial against a captured Tiger II, and the U.S. gun was significantly better at penetrating the Tiger II. The report is published on the Russian Battlefield site. Comparing Russian 85mm HVAP to 85mm APBC against vertical targets results in: 100m: 165mm for HVAP, 139mm for APBC 500m: 137mm for HVAP, 123mm for APBC 1000m: 107mm for HVAP, 105mm for APBC 1500m: 81mm for HVAP, 91mm for APBC Inside 500m, 85mm HVAP has a higher probability to defeat the Tiger mantlet than 85mm APBC. For U.S. 76mm APCBC: 100m: 239mm for HVAP, 125mm for APCBC 500m: 208mm for HVAP, 116mm for APCBC 1000m: 175mm for HVAP, 106mm for APCBC 1500m: 147mm for HVAP, 97mm for APCBC

The U.S. 76mm HVAP and British APDS rounds (combat and experimental) used tungsten cores which were half the diameter of the carrier (76.2mm 17 pdr APDS fired a 38.1mm tungsten core). Russian tungsten core diameters appear to assume a lower percentage of the carrier diameter as the gun size increases: 45mm: 19.1mm core and 45mm carrier, 42.4% core-to-carrier percentage 57mm: 24.1mm core and 57mm carrier, 42.3% 76.2mm: 27.94mm core and 76.2mm carrier, 36.7% 85mm: 27.77mm core and 85mm carrier, 32.7% The relationship between core and carrier diameter may have been related to tungsten conservation, although other factors are possible. The Russian 76.2mm tungsten core round used a 0.484 kg tungsten core with a 0.149 kg steel follow-up plug which would add its full weight to the penetration of vertical plates as if it were tungsten, and which may have been a conservation effort. It is also noted that the Russians stayed with the arrowhead type of tungsten core HVAP round after the Germans switched.

The following data pertains to WW II Russian 85mm and American 76mm HVAP rounds: Russian 85mm HVAP ================= Fired at 1040 m/s 0.65 kg tungsten core 27.94mm core diameter in American analysis, 27.77mm from Russian data. 100m, 1009 m/s, 165mm vertical target penetration 300m, 947 m/s, 150mm 500m, 887 m/s, 137mm 1000m, 744 m/s, 107mm 1500m, 614 m/s, 81mm American 76mm HVAP ================== Fired at 1037 m/s 1.765 kg tungsten core 38.1mm core diameter 100m, 1018 m/s, 240mm vertical target penetration 300m, 981 m/s, 226mm 500m, 939 m/s, 211mm 1000m, 848 m/s, 179mm 1500m, 756 m/s 149mm Comparing the two HVAP rounds the American 76mm ammunition holds a greater percentage of its muzzle velocity at range and also outpenetrates 85mm HVAP by a significant amount. The American HVAP tungsten core is larger and heavier than the Russian core. The British 17 pdr APDS tungsten core had similar dimensions and weight when compared to the American 76mm HVAP. The above data shows that larger guns did not always fire more effective tungsten core ammo during WW II. The American HVAP penetration velocity and penetration data is from TM9-1907, the Russian 85mm HVAP figures were provided by Miles Krogfus. If the Russian tungsten core data and velocity is used for penetration estimates based on the U.S. 76mm HVAP at 0m and 0 degrees (247mm penetration at 1037 m/s), the resulting DeMarre equation estimates are: 100m, 163mm predicted (165mm actual) 300m, 149mm predicted (150mm actual) 500m, 136mm predicted (137mm actual) 1000m, 106mm predicted (107mm actual) 1500m, 80mm predicted (81mm actual) The Russian 85mm HVAP tungsten core was expected to perform with the same ballistic characteristics as the American 76mm HVAP, which suggests a similarity of material quality. Previous posts on this forum regarding Russian 45mm and 76.2mm HAVP (or APCR) showed that the ammunition performed with the same ballistic penetration characteristics as American 76mm HVAP beyond close range, but the Russian tungsten cores appeared to perform in an inferior manner once the impact velocity exceeded about 700 m/s.

Thanks for the great drawing that brings several points into focus. What is the source for the PzKpfw III drawing?

The World War II penetration data figures presented in the CM games appear to represent the 50% success thickness that can be defeated. If a gun with 82mm penetration hits an 82mm plate flat on, half the hits get completely through and half don't. The 50% success criteria averages the highest velocity that results in a failure with the lowest success velocity. The penetration probability curve is a bell shaped normal distribution, and actual "standard deviations" for the curve against good armor range from 4% during U.S. trials with 37mm APCBC to 7% for Russian 76.2mm APBC ammo. Firing tests against Tiger resulted in a "standard deviation" of 5.65%. The "standard deviation" indicates the spread of the curve, where 68% of the results are within one "standard deviation" (plus or minus) from average. If half the hits succeed when the penetration equals the armor effective resistance (after quality multipliers and slope effects), then the following table applies: penetration equals armor resistance, 50% success penetration -0.5 std deviations less than resistance, 31% success penetration -1 std deviations less, 16% success penetration -1.5 std deviations less, 7% success penetration -2 std deviations less, 2% success penetration -2.5 std deviations less, 0.6% success penetration -3 std deviations less, 0.1% penetration 0.5 std deviations over resistance, 69% success penetration 1 std deviation over resistance, 84% success penetration 1.5 std deviations over, 93% success penetration 2 std deviations over, 98% success penetration 2.5 std deviations over, 99.4% success penetration 3 std deviations over, 99.9% success Actual firing tests against the Tiger side armor by the Americans, British and Russians show an average resistance of 84.5mm with a standard deviation of 5.65%. The 84.5mm takes into account thickness variations above the 80mm design spec and ballistic advantages. If the Sherman 75mm hits the Tiger side armor at 750m range with APCBC and no side angle, the penetration is 77mm and the armor resistance is 84.5mm. The penetration is 8.88% less than the resistance. With a standard deviation of 5.65%, the Sherman penetration is 8.88/5.65 or 1.57 standard deviations below the resistance. The penetration probability works out to 5.8%. Reports on the combat where Michael Wittmann's Tiger was knocked out suggest that Sherman 75mm APCBC rounds were bouncing harmlessly off the Tiger side armor at 700 to 800 yards, which could be a function of inadequate penetration at range, side angles to the shots and "unlucky rolls". If the standard deviation for the 750m hit on the Tiger side armor was 4% or 7%, the corresponding penetration probabilities would be 1.3% and 10.2%. Poor or flawed armor not only reduces the effective resistance of armor, but the standard deviation appears to be about 60% greater than the figure which would apply to good armor (quality = 1.00). When rounds do defeat armor despite less penetration than the resistance and the penetration probability is very low, chances are good the round will have little remaining energy when it passes through the armor, and the shell structure may be sufficiently damaged to prevent the HE burster from going off. At Kursk, one of several 76.2mm hits on the side of a Ferdinand made it into the vehicle but did little damage.

The World War II penetration data figures presented in the CM games appear to represent the 50% success thickness that can be defeated. If a gun with 82mm penetration hits an 82mm plate flat on, half the hits get completely through and half don't. The 50% success criteria averages the highest velocity that results in a failure with the lowest success velocity. The penetration probability curve is a bell shaped normal distribution, and actual "standard deviations" for the curve against good armor range from 4% during U.S. trials with 37mm APCBC to 7% for Russian 76.2mm APBC ammo. Firing tests against Tiger resulted in a "standard deviation" of 5.65%. The "standard deviation" indicates the spread of the curve, where 68% of the results are within one "standard deviation" (plus or minus) from average. If half the hits succeed when the penetration equals the armor effective resistance (after quality multipliers and slope effects), then the following table applies: penetration equals armor resistance, 50% success penetration -0.5 std deviations less than resistance, 31% success penetration -1 std deviations less, 16% success penetration -1.5 std deviations less, 7% success penetration -2 std deviations less, 2% success penetration -2.5 std deviations less, 0.6% success penetration -3 std deviations less, 0.1% penetration 0.5 std deviations over resistance, 69% success penetration 1 std deviation over resistance, 84% success penetration 1.5 std deviations over, 93% success penetration 2 std deviations over, 98% success penetration 2.5 std deviations over, 99.4% success penetration 3 std deviations over, 99.9% success Actual firing tests against the Tiger side armor by the Americans, British and Russians show an average resistance of 84.5mm with a standard deviation of 5.65%. The 84.5mm takes into account thickness variations above the 80mm design spec and ballistic advantages. If the Sherman 75mm hits the Tiger side armor at 750m range with APCBC and no side angle, the penetration is 77mm and the armor resistance is 84.5mm. The penetration is 8.88% less than the resistance. With a standard deviation of 5.65%, the Sherman penetration is 8.88/5.65 or 1.57 standard deviations below the resistance. The penetration probability works out to 5.8%. Reports on the combat where Michael Wittmann's Tiger was knocked out suggest that Sherman 75mm APCBC rounds were bouncing harmlessly off the Tiger side armor at 700 to 800 yards, which could be a function of inadequate penetration at range, side angles to the shots and "unlucky rolls". If the standard deviation for the 750m hit on the Tiger side armor was 4% or 7%, the corresponding penetration probabilities would be 1.3% and 10.2%. Poor or flawed armor not only reduces the effective resistance of armor, but the standard deviation appears to be about 60% greater than the figure which would apply to good armor (quality = 1.00). When rounds do defeat armor despite less penetration than the resistance and the penetration probability is very low, chances are good the round will have little remaining energy when it passes through the armor, and the shell structure may be sufficiently damaged to prevent the HE burster from going off. At Kursk, one of several 76.2mm hits on the side of a Ferdinand made it into the vehicle but did little damage.

The World War II penetration data figures presented in the CM games appear to represent the 50% success thickness that can be defeated. If a gun with 82mm penetration hits an 82mm plate flat on, half the hits get completely through and half don't. The 50% success criteria averages the highest velocity that results in a failure with the lowest success velocity. The penetration probability curve is a bell shaped normal distribution, and actual "standard deviations" for the curve against good armor range from 4% during U.S. trials with 37mm APCBC to 7% for Russian 76.2mm APBC ammo. Firing tests against Tiger resulted in a "standard deviation" of 5.65%. The "standard deviation" indicates the spread of the curve, where 68% of the results are within one "standard deviation" (plus or minus) from average. If half the hits succeed when the penetration equals the armor effective resistance (after quality multipliers and slope effects), then the following table applies: penetration equals armor resistance, 50% success penetration -0.5 std deviations less than resistance, 31% success penetration -1 std deviations less, 16% success penetration -1.5 std deviations less, 7% success penetration -2 std deviations less, 2% success penetration -2.5 std deviations less, 0.6% success penetration -3 std deviations less, 0.1% penetration 0.5 std deviations over resistance, 69% success penetration 1 std deviation over resistance, 84% success penetration 1.5 std deviations over, 93% success penetration 2 std deviations over, 98% success penetration 2.5 std deviations over, 99.4% success penetration 3 std deviations over, 99.9% success Actual firing tests against the Tiger side armor by the Americans, British and Russians show an average resistance of 84.5mm with a standard deviation of 5.65%. The 84.5mm takes into account thickness variations above the 80mm design spec and ballistic advantages. If the Sherman 75mm hits the Tiger side armor at 750m range with APCBC and no side angle, the penetration is 77mm and the armor resistance is 84.5mm. The penetration is 8.88% less than the resistance. With a standard deviation of 5.65%, the Sherman penetration is 8.88/5.65 or 1.57 standard deviations below the resistance. The penetration probability works out to 5.8%. Reports on the combat where Michael Wittmann's Tiger was knocked out suggest that Sherman 75mm APCBC rounds were bouncing harmlessly off the Tiger side armor at 700 to 800 yards, which could be a function of inadequate penetration at range, side angles to the shots and "unlucky rolls". If the standard deviation for the 750m hit on the Tiger side armor was 4% or 7%, the corresponding penetration probabilities would be 1.3% and 10.2%. Poor or flawed armor not only reduces the effective resistance of armor, but the standard deviation appears to be about 60% greater than the figure which would apply to good armor (quality = 1.00). When rounds do defeat armor despite less penetration than the resistance and the penetration probability is very low, chances are good the round will have little remaining energy when it passes through the armor, and the shell structure may be sufficiently damaged to prevent the HE burster from going off. At Kursk, one of several 76.2mm hits on the side of a Ferdinand made it into the vehicle but did little damage. [ March 19, 2004, 04:38 PM: Message edited by: rexford ]

CMAK tends to give the turret front armor thickness for tanks, cause all tanks have a turret front but a few don't have a big mantlet I guess, and the usen the mantlet thickness for the actual penetration calculations. Tiger is one example, 100mm turret front "reinforced". The mantlet is much thicker than 100mm on almost all areas when backing plates are cranked in, and the CM games appear to use the mantlet armor when the "turret front" is hit.. With regard to turret armor in general, weight is a big limit and many turret fronts are significantly more vulnerable than the hull front due to weight limits: Panther, T34, T34/85, IS-2, Tiger II. Tiger is an oddity because the mantlet is better protected than the hull front. The exact calculations for 37mm/40 degrees are: 37mm armor at 40 degrees resists a 2 pdr AP hit like 59mm vertical, and 2 pdr AP penetrates 59mm of vertical face-hardened armor at 190m or 208 yards. Close to Jentz information. Various discussions of PzKpfw III mantlets state that the 37mm armed models had an internal mantlet, and the 50mm armed tanks had an external mantlet. There may well be a splash guard between the external mantlet on PzKpfw IIIH and the turret interior to reduce the chance that HE shell fragments and bullets and mantlet flaking will injure the crew. British records on PzKpfw III show a 37mm mantlet on the PzKpfw IIIH and 50mm mantlet on PzKpfw IIIJ-M, with a 57mm turret front on PzKpfw IIIL,M. The turret front on PzKpfw IIIJ is listed as 30mm. Our book uses 35mm for PzKpfw IIIE-H mantlet but the British records show 37mm.

American armor started out very poor, the chemical compositions could result in a crystalline brittle structure at design hardnesses. The quality control and quench procedures were also not conducive to good quality plate. Starting October 1943, American armor makers HAD to apply improved quality control procedures and greatly improved quench processes, which is why Shermans with 47 degree glacis armor are much better than the Shermans with 56 degree glacis plates. In addition, the 56 degree Shermans often used multi-piece glacis armor with lots of weld lines that provided weak areas for hits, and the pieces often included cast armor which would be quite inferior to rolled when 50.8mm castings were hit by German 75mm APCBC. American armor got better as the war progressed, German armor may have had an increased probability of being less than optimum.

I would add that American tests show that U.S. 90mm APCBC and British 17 pdr APCBC would not penetrate a Panther glacis that was not cracked, even at extremely short range. So the penetration resistance of the plate was good against 90mm and 76.2mm hits, but if it cracked a follow up hit near or on the crack could result in a penetration. And the tremendous impact from a 122mm or 152mm hit on a brittle glacis plate could result in a complete penetration of previously uncracked Panther glacis armor.

The BIOS report indicates that alloy shortages in Germany lead to an alternative timed quench system. Alloys allow one to get away with small mistakes without compromising the quality of the armor, but the timed quench system was supposed to make up for alloys with precisely timed dunk and dry procedures. A plate would be dunked for so many seconds, then pulled out for so many seconds, then the whole thing again. A few seconds too long or too short and something may go wrong. BIOS indicates that with timed quench the Germans were able to retain the penetration resistance of their plates with reduced alloys, and in most cases the impact toughness would be good. According to BIOS: German testing of 80mm plates took place with uncapped 50mm rounds, which may have shattered. Anyway, an 80mm plate would be taken out and fired upon with 50mm uncapped Pzgr 39, and if it failed (allowed for a crack to go completely through the plate) another plate was tested. If that plate passed the lot passed the first stage. Then a plate was hit with 75mm rounds that completely penetrated and the hole had to be free of signs of brittleness. Could bad plates pass such a testing process? At Isigny, two of three Panther glacis cracked after a few hits. British and American firing tests against other captured Panthers show signs of weld failures (alloys in welds were reduced during early 1944), and glacis plate cracking. Interestingly enough, the lower front hull nose plate on the Panther almost never cracks after all sorts of hits. Our theory is that the size of the Panther glacis plates made it extremely sensitive to small errors in the timed quench process, which could occur due to bombing, inexperienced workers, etc. And the Panther front nose armor was smaller and less susceptible to boo-boo's. It should be noted that some JagdPanther glacis plates were measured at 220 Brinell Hardness, which may have been an attempt to reduce cracking tendencies through reduced hardness. There aren't many firing tests against the Jagdpanther glacis so one cannot really say much about the cracking tendency. During British firing tests a glancing hit on the Panther turret side that rebounded away caused a large square area to crack. Now, American metallurgical tests of Panther and Tiger armor show very low Charpy V-Notch impact test results. According to post-WW II American armor acceptance curves many Panther and Tiger armor plates would have been rejected. But Tiger armor was not really mass-produced, and probably had more alloys than the mass production Panther glacis armor, and combat in Russia showed that Tigers could take all sorts of punishment from Russian tanks and guns without having the armor break up. So I would guess that Tigers tended to have good quality armor, and the British say that an occasional Tiger plate was bad but most was good stuff. And the Panther glacis tended to be brittle on a certain percentage of tanks which increased as the alloy situation got worse.

The British data I posted was based on the Critical Velocity for 50% success with German production ammo, where half the hits meet the penetration criteria and half don't. Plate hardness differences would not amount to much. There have been many discussions on the web regarding what it means when one penetration test requires that 80% of a round make it fully through the plate, another uses 100%, and still another uses 51%. There is, according to our readings of American discussions on penetration success criteria, very little difference between requiring that 51%, 80% or 100% of a round make it completely through. The criteria which requires that a certain percentage make it through the plate is put into the guidelines to eliminate the result where the round sticks in the plate but the nose breaks off and goes completely through. By requiring that a certain percentage of the ammo make it through you rule out partial penetrations where only a small bit of the round (nose) passes the plate. If at least 51% of a round makes it through the plate chances are a much higher percentage succeeds in most cases. German test data actually required that the best quality round penetrate the plate five times in a row in a condition where the HE was capable of detonating properly. When you see that the Tiger 88mm Pzgr 39 penetrates 120mm at 30 degrees and 100m, that means that the best quality 88mm ammo penetrates 120mm/30 degree five times in a row at the velocity associated with 100m. To convert the 120mm/30 degrees for Tiger best quality 88mm apcbc to 50% success with production ammo, one decreases the penetration to convert to production ammo and then increases the result because five consecutive successes would be against less armor than a 1-in-2 success rate.

The PzKpfw IIIH frontal protection has been discussed quite a bit in the bat-a-rounds between JasonC and myself. British firing tests in Cairo during May 1942 showed that the 2 pdr AP round would not penetrate the PzKpfw IIIH hull front at 200 yards. The same firing tests with 37mm APCBC, 75mm AP and APCBC from a Grant, a Grant 75mm firing the German 75mm APC round (75L24 ammo) and 6 pdr AP from the early shorter barreled gun (2700 fps muzzle velocity) showed that 32mm/30mm on the PzKpfw IIIH drive plate resisted like a single 69mm face-hardened plate. Since the 2 pdr AP would only penetrate 67mm or so of face-hardened armor at 0 yards, don't expect many defeats of the IIIH hull front. The PzKPfw IIIH mantlet and hull front don't really overlap much. The mantlet is 37mm face-hardened and has a 40 degree slope from vertical in one area (it isn't really rounded at the upper and lower areas, just near the middle), which would resist 2 pdr AP hits like close to 60mm face-hardened, and which may account for the 200 yard penetration range Jentz mentions. But half of the IIIH mantlet was not very well sloped, and would be much more vulnerable. The data Jentz refers to probably didn't include many hits on the less sloped areas of the IIIH mantlet. The hull front of a PzKpfw IIIH makes up the majority of the frontal target aspect, so most hits would land on either the hull front or the highly sloped mantlet area. At close range the 2 pdr would tend to hit what it aimed at, namely the driver plate, due to the high muzzle velocity (for North Akrika during early to mid 1942).

Combining penetration data at 30 degrees from jentz' Dreaded Threat and the Encyclopedia of German Tanks of World War II: Early War Flak firing 9.54 kg Pzgr round 97mm at 100m, 93mm at 500m, 87mm at 1000m Later war Flak firing 10.2 kg Pzgr 39 round 127mm at 100m, 117mm at 500m, 106mm at 1000m Tiger 88mm firing 10.2 kg Pzgr 39 round 120mm at 100m, 110mm at 500m, 100mm at 1000m The above statistics suggest that the early war Flak gun fired an inferior round compared to the later war Flak, and the later war Flak was firing at about 810 m/s muzzle velocity compared to 780 m/s for the Tiger.

Combining penetration data at 30 degrees from jentz' Dreaded Threat and the Encyclopedia of German Tanks of World War II: Early War Flak firing 9.54 kg Pzgr round 97mm at 100m, 93mm at 500m, 87mm at 1000m Later war Flak firing 10.2 kg Pzgr 39 round 127mm at 100m, 117mm at 500m, 106mm at 1000m Tiger 88mm firing 10.2 kg Pzgr 39 round 120mm at 100m, 110mm at 500m, 100mm at 1000m The above statistics suggest that the early war Flak gun fired an inferior round compared to the later war Flak, and the later war Flak was firing at about 810 m/s muzzle velocity compared to 780 m/s for the Tiger.

QUALITY OF RUSSIAN TUNGSTEN CORE AMMO While Russian AP and APBC ammunition during WW II was much softer than Allied projectiles and penetrated less, the tungsten core rounds appear to been similar with some notable drawbacks at higher impact velocities. Using the DeMarre equation for vertical penetration and base data for U.S. 76mm HVAP, we estimated the Russian 45mm and 76.2mm APCR penetration at various ranges and compared to published Russian figures and our previous estimates. 45mm L46 M37 APCR: 19.1mm core diameter, 0.2534 kg core weight, 970 m/s muzzle velocity. ===================================================================== 1. DeMarre Equation Estimates 118mm at 0m, 105mm at 100m, 93mm at 200m, 82mm at 300m, 73mm at 400m, 66mm at 491m 2. Published Russian Figures (30 degrees converted to vertical using 1.4 slope multiplier) 104mm at 0m, 99mm at 100m, 92mm at 200m, 84mm at 300m, 76mm at 400m, 66mm at 491m Note: DeMarre estimate close to Russian figures at 200m+ with reductions to estimates at close range (less effective than material used in U.S. 76mm HVAP) 3. Our Estimates (based on firing tests vs Tiger and Russian penetration figures) 96mm at 0m, 89mm at 100m, 82mm at 200m, 75mm at 300m, 72mm at 400m, 66mm at 491m Note: penetration reduced at ranges below 491m compared to DeMarre estimate (less effective than material used in U.S. 76mm HVAP) Summary: Russian 45mm APCR performance appears to be similar in quality to U.S. 76mm HVAP when impact velocity is sufficiently low (below 700 m/s) but loses penetration at closer ranges. 45mm APCR used against Tiger seems to be lower quality than ammo used for published Russian figures unless Tiger side armor was resisting 45mm APCR like 92mm due to hardness of plates. In U.S. tests with 90mm HVAP against 203mm of vertical plate, 339 Brinell Hardness armor resisted with about 11% more effective thickness than 240 Brinell. Early Tigers carried side armor with above 300 Brinell Hardness which could have added to the resistance against small brittle projectiles such as 45mm tungsten core. 76.2mm APCR: 27.94mm core diameter, 0.484 kg tungsten core/ 0.15 kg follow-up plug, 965 m/s velocity. ============================================================================ 1. DeMarre Equation Estimates 150mm at 0m, 136mm at 100m, 124mm at 200m, 113mm at 300m, 103mm at 400m, 94mm at 500m, 59mm at 1000m 2. Russian Figures 104mm at 0m, 102mm at 100m, 100mm at 200m, 98mm at 300m, 97mm at 400m, 92mm at 500m, 60mm at 1000m Summary: 76.2mm APCR suffers a penetration reduction relative to DeMarre estimate at ranges below about 500m, suggesting about same tungsten core quality as U.S. 76mm HVAP material as long as impact velocity is less than 700 m/s. Interesting aspect of 76.2mm APCR round is the combination of a 0.484 kg tungsten core and 0.15 kg follow-up steel plug, where the steel plug would help conserve tungsten and add its weight to vertical penetration. It is not clear to what degree the steel plug would assist the tungsten core on angled hits, where stress on joint might cause separation of the two parts and decrease the effectiveness. Impacts on 57mm APCR Effectiveness ============================ The 57mm APCR round was fired at 1200 fps, which is far above the 700 m/s threshold where 45mm and 76.2mm APCR rounds appeared to lose penetration relative to the DeMarre estimates. 57mm APCR would reach 700 m/s velocity at about 1150m range. Published Russian penetration figures for 57mm APCR show 140mm at vertical and 500m, while the expected frontal penetration range for the ammo presented in the instructions for combating Tiger tanks is 500m (which suggests close to 100mm penetration at 500m). It should be noted that American, German and British tungsten core rounds do not appear to vary too far from the DeMarre equation estimates as the impact velocity approaches the muzzle velocity, which suggests that the observed penetration variations with Russian 45mm and 76.2mm APCR may have been limited to that country’s projectiles.

The driver viewing glass was often backed up by an armor plate a short distance behind the opening and glass, and the driver didn't see straight through the port but looked indirectly. The viewing port on the hull front would be a weak point for penetrations. On early Tiger tanks the area around the gun sight openings in the mantlet was scooped out, and presented about 75mm thickness minus edge effects.

The German penetration estimates in our book for vertical plate are between the two sets presented in the previous post for some guns and above both sets for 88mm APCBC: 75L43 APCBC 100m 133mm 500m 121mm 1000m 107mm 75L48 APCBC 100m 135mm 500m 123mm 1000m 109mm 75L46 APCBC 100m 146mm 500m 133mm 1000m 118mm 75L70 APCBC 100m 185mm 500m 168mm 1000m 149mm 88L56 APCBC (tank gun) 100m 162mm 500m 151mm 1000m 138mm 88L71 APCBC 100m 232mm 500m 219mm 1000m 204mm We compared our figures to estimates made by the German penetration equations and the results seemed close to our estimates.