rexford

The following web site has some penetration vs angle curves for German 380mm APCBC ammo, which brings up an interesting aspect of slope effect analysis. http://www.warships1.com/W-INRO/INRO_Hood_p2.htm Our base data for APCBC slope effects is limited to a range where the T/D ratio ranges from low to high figures, but does not really reach very low ratio's. I have read where thin plate gains added resistance from stretching, which suggests that our slope multiplier vs T/D ratio's for each angle may not work well at very low T/D. Here is an analysis of 380mm APCBC slope effects vs T/D ratio with comparison to estimates using our equations; 380mm APCBC at 250 m/s penetrates 200mm at vertical and 80mm at 57 degrees from vertical 2.50 slope multiplier when T/D = 0.211 (80mm/380mm) If U.S. 75mm APCBC hit 16mm at 57 degree armor (T/D = 0.211), the slope effect would be about 1.88 from our equations. 380mm APCBC at 170 m/s penetrates 120mm at vertical and 40mm at 67 degrees from vertical 3.00 slope multiplier when T/D = 0.105 (40mm/380mm) If U.S. 75mm APCBC hit 8mm plate at 67 degrees (T/D = 0.105), the slope effect would be 2.13 from our equations. 380mm APCBC at 120 m/s penetrates 80mm at vertical and 40mm at 57.5 degrees from vertical 2.00 slope multiplier when T/D = 0.105 (40mm/380mm) U.S. 75mm APCBC against 8mm at 57.5 (T/D = 0.105) would have a slope effect of 1.63 from our equations. It may be that our models don't consider hits on very thin armor where the stretching of the plate comes into play. Our base data may not go to really low T/D ratio's.

I went outside with my 4x laser rangefinder binoculars and tested the theory. A 30' high pole at 600' was found, which was measured at 15mm with a ruler held 305mm infront of my eyeball. When the 4x binoculars were used and a ruler was used to measure the perceived height, the measurement was 60mm, while theory predicted 61mm.

One aspect of aimed fire which places limits on successful targeting is the size of the perceived target on a gunsight. At 100m range with a 2.5x magnification gunsight, a 2.2m target would appear to be 0.66 inches high, or 16.8mm. Hold a ruler out 1 foot (30.5cm) infront of you and look at a height of 16.8mm or 0.66 inches. The target is fairly large and would allow for aimed fire. So Wittmann was able to aim at T34 turret rings in his StuG IIIA and hit them, but the range was, and had to be, very close to raise the success probability to the point where the time taken aiming at and hitting T34's was less than the T34 reaction time. At 1000m range, the perceived target height is one-tenth as high as the 100m case, 0.066 inches or 1.68mm for a 2.2m target. One is lucky if they can repeatedly place the crosshairs on the target center of mass at 1000m let alone aim at the center of the turret. Perceived height at 12 inches (or 305mm) from the eyeball equals: (actual height in meters x 12 inches (or 305mm) x gunsight magnification) divided by (range to target in meters). At 100m, a 2.2m high target with 2.5 magnification would be 2.2m x 305mm x 2.5/100m, or 16.8mm in perceived height. Having a 10x gunsight changes things for aimed fire at 1000m. 2.2m high target at 1000m appears to be 6.71mm high (0.26 inches) in 10x gunsight. A Jagdpanther with an educated and nerves-of-steel crew might be able to aim at the center of the IS-2 turret front if background contrast made the target stand out enough for aimed fire (which is another limit on high efficiency aimed fire, you have to be able to clearly make out the target outline). Aimed fire ability at range is limited by gunsight magnification and other factors, which answers the question as to why 75mm and 88mm guns were needed when 37mm guns could aim at turret rings and land a hit or two given a large number of shots (or an incredibly short range). With the 75mm L70 gun a hit on the front of a T34 at 1000m is a kill most of the time and the perceived target is fairly small, with a 37mm gun aimed fire probabilities are ridiculously low at 1000m. Perceived Height of 2.2m High Target with 2.5x Magnification Gunsight vs Range 25m, 67.1mm 50m range, 33.6mm 100m, 16.8mm 200m, 8.4mm 500m, 3.4mm 1000m, 1.7mm 1500m, 1.1mm 2000m, 0.84mm 3000m, 0.56mm Takes good eyes and a steady hand to repeatedly aim at center of mass at 3000m, let alone try to hit the gun mantlet center. =========================================================== To test the validity of the perceived height equation, measure the actual height of an object across the room, such as a 220mm high lampshade at 8.5' or 2.591m. Hold a ruler 1' or 305mm away from your eyes and measure the perceived height, which is about 25mm (my hand shakes early in the morning so greater accuracy in reading the scale is not possible). According to the equation, the perceived height at 305mm infront of the eye would be: 220mm x 305mm/2591mm, or 25.9mm. Aiming at the center of the lamp or a specific point on it at 2.6m distance is possible, place the lamp at 1000m and things change radically even with 2.5x gunsights.

Thanks for looking into 37mm cap question.

Did German 37mm AP have a ballistic windscreen cap to reduce air resistance? Thanks.

Paul Lakowski posted the following on the Yahoo! Tankers forum for a thread regarding whether the Germans trained crews to use aimed fire. I am attempting to obtain a reference: "I was reading an account of a squadron of Pz-35t encountering a troop of KV heavy tanks..the CO orders them to concentrate fire on the turret ring and sure enough two tanks get there turrets jammed while the other runs away!Not one of the puny Cz tanks are hit....it did happen! Although for obvious reasons it would be preferable to penetrate the target."

During early 1942, the Germans produced T34 like armor with same composition, and hardened to same level (about 450 Brinell). 37mm and 50mm anti-tank guns were fired at an assumed range of 100m, which was the standard for penetration tests. Following results were obtained for 37mm AP and indicate the angle at which complete penetration is not likely ("sicher" criteria): 40.6mm plate, 40.0 degrees from vertical 40.9mm plate, 40.5 degrees 42.1mm plate, 40.0 degrees 43.2mm plate, 34.5 degrees 45.8mm plate, 21.0 degrees 47.1mm plate, 19.0 degrees 47.2mm plate, 20.0 degrees 51.9mm plate, 10.5 degrees 53.0mm plate, 09.0 degrees 53.3mm plate, 09.0 degrees Complete penetration would occur a few degrees below the "sicher" angle presented above. Against T34 high hardness 45mm plates, 37mm AP will not penetrate armor sloped at 30 or 40 degrees at 100m, will penetrate 45mm of vertical plate. If 37mm AP is uncapped (no ballistic windscreen), a trajectory spreadsheet estimates velocity vs range profile as: 745 m/s at 0m 708 m/s at 100m 651 m/s at 250m 561 m/s at 500m This suggests that the thicknesses needed for protection against complete penetration ("sicher" criteria) would decrease by following factors relative to 100m figure: 100m, 100% 250m, 88% 500m, 72% At 100m, 250m and 500m range, 21 degree impacts by 37mm AP would be defeated by 45.8mm, 40.4mm and 33.0mm. The maximum penetration of 45.8mm plate by 37mm AP occurred at an angle of 16 degrees from vertical during tests, with failure at 21 degrees. This suggests that 100m successes against 45mm would be restricted to a small angle range, 0 to 18 degrees from armor perpendicular, and the range would shrink very quickly as distance to armor increased. If 45.8mm can be penetrated at an angle of 16 degrees at 100m, penetration at 0 degrees would be expected at a maximum range of about 200m. So 37mm AP might not be expected to penetrate a 45mm high hardness plate above 200m, if the round is uncapped. Miles Krogfus provided the report which contained the data used in this post. [ February 01, 2003, 03:36 AM: Message edited by: rexford ]

Some of the T34-vs-PzKpfw IIIg controversey can be traced back to playtest comments provided by this writer. U.S. tests with high hardness armor (450 Brinell), such as carried by T34, indicated that if the projectile diameter was greater than the armor thickness, the armor lost resistance compared to good quality medium hardness material. Equations based on the U.S. tests suggest that when 50mm AP hits 45mm at 450 Brinell Hardness, the armor should lose 17% of the resistance. During 1942, the Germans prepared armor plates in the 42mm to 53mm thickness range using Russian steel composition and hardening to 450 Brinell. The plates were then fired on by 37mm and 50mm guns at various angles, with some unusual results. 50mm AP rounds at 100m fully penetrated 47.2mm at 60.5 degrees, and 42.1mm at 65 degrees. 16 hits failed to penetrate. So 2 of 18 hits fully penetrate armor that should never have been completely defeated. These test results suggest that the Russian armor would resist with less than optimum performance. The above is the basis of my theory on high hardness armor deficiencies, which was brought out during the playtest period. With armor deficiency theory, 75L43 APCBC penetrates T34 high hardness glacis at 1600m, if resistance is assumed to be the same as medium hardness good armor 75L43 is limited to 460m. 75L43 case suggests that high hardness deficiency is real. ================================================ Now, when 50mm AP is fired against 40mm plates at 40 degrees in German 1942 tests, a very easy target, 2 of 5 hits fail to fully pierce the armor. Shatter gap, from the sound of it. Penetration data suggests that early war German AP rounds were softer and more prone to shatter than the later war stuff. Shatter gap occurs when a round has more than enough velocity and mass to defeat the armor, but the back pressure from quickly moving armor causes the projectile nose to break apart. 50L42 AP penetrates about 55mm at 500m, 45mm at 40 degrees resists like 71mm vertical plate if medium hardness, and 59mm vertical if U.S. high hardness modifiers are applied. Say 50mm L42 is firing on T34 side plates at 250m, the penetration is 66mm, the high hardness resistance after modifier is 59mm, the round should penetrate. No, it should not! Shatter gap tests show that when uncapped ammo overpenetrates the armor by 1.05 to 1.30 or so (but sometimes much, much higher), the projectile stands a high probability of breaking up on the armor. When rounds overpenetrate by 1.01 to 1.04, or greater than 1.30, expect penetrations. At 250m, 50L42 AP overpenetrates 45mm at 40 degrees by 66mm/59mm, or 1.12. At 100m, 50L42 AP overpenetrates T34 side hull by 73mm over 59mm, or 1.24, so a good chance the rounds will break up and fail due to shatter gap. At 500m, 50mm L60 AP overpenetrates T34 side hull armor by 77mm/59mm, or 1.31. If the overpenetration ratio's hold with 50mm L60, the gun should penetrate from 0m to 500m, and then fail from 500m to nearly 1000m. Then it should penetrate some at ranges beyond 1000m. The above cases show that 50mm AP failures against T34 side hull can be explained on the basis of shatter gap. In German armor acceptance tests against 80mm vertical plate, 50mm uncapped AP was expected to fail even though it could fully penetrate over 100mm in other tests. Explanation is shatter gap. In British tests against Tiger side armor, 2 pounder AP that was capable of defeating over 80mm of vertical plate failed to fully break through 62mm of Tiger lower hull side plate. Shatter gap. [ January 31, 2003, 06:17 PM: Message edited by: rexford ]

Did the person state that he was trained to aim at the turret ring?

Some time ago we had a discussion on German use of aimed fire, with the turret ring being a choice area, and someone discussed the subject with a relative who had been a 37mm PaK crewmen. He stated that his crew was trained to aim at the turret ring, because that area was very vulnerable and a hit on that location could immobilize a KV or T34 tank. I am looking for input with regard to showing that German crews did use turret ring aim, and were taught the procedure. Thanks for helping out on this. Lorrin [ January 20, 2003, 11:23 AM: Message edited by: rexford ]

You're correct. ASL used the 160mm figure that was popular at the time, but they also were restricted by an armor system that only allowed the turret rating to be one change increment higher or lower than the hull. The 160mm thickness for mantlet is no longer given any weight.

Recent discussions and research on other forums strongly suggests that the IS-2 tanks had 110mm mantlets, and IS-2 Model 1944 had a front lower hull thickness of 100mm cast or 90mm rolled. These figures contrast with the British Intelligence report (100mm mantlet and 127mm front lower hull) that I used to swear by. I asked Vasiliy Fofanov to look in his Russian books on armor thickness and he replied (on Yahoo! Tankers site), "Zheltov et al. confirms, it is 100mm cast or 90mm rolled." Many drawings on Russian Battlefield show 100mm lower front hull on IS-2 Model 1944, see http://www.battlefield.ru/is2_1.html, FIGURE 6. Cross-sections showing different arrangements for joining the frontal armour plates. Unfortunately, another drawing on the same page shows 120mm for front lower hull on IS-2 with 60 degree glacis. Confusion reigns supreme! Thanks to Dima for bringing this subject to my attention. [ January 15, 2003, 09:49 PM: Message edited by: rexford ]

The British BIOS report brings to light an interesting aspect of the German penetration figures for 37mm guns. While the U.S. and British based most of their penetration data on a 50% success rate, the Germans required that ten straight 37mm hits penetrate within a narrow velocity band. This means that the actual penetration for 37mm guns at 50% success would be about 21% higher than the listed figures (see books by Jentz or Chamberlain) at 30 degrees, and about 28% higher at 0 degrees. [ January 15, 2003, 09:56 PM: Message edited by: rexford ]

Those are the ratio's of board penetrations after tests of 82mm and 81mm mortars.

Miles Krogfus, who does some really great research on German, ALlied and Russian arms and armor using original documents recently sent me a copy of a U.S. analysis of Russian ordnance and armor (1953, By a metallurgist named Hurlich). Following information and data is really telling with regard to 82mm Russian mortar: 1. Russian mortar rounds used cast iron which put out more fragments than forged steel used by U.S.81mm mortar, and shape of fragments from cast iron were of optimum shape (cast fragments tended to be small and rounded instead of long splinters from forged steel) 2. Russian mortar rounds appear to be designed for maximum fragmentation instead of blast 3. At 20' from blast point, Russian 82mm mortar puts out 4.3 times the number of effective hits of U.S. 81mm mortar which uses forged steel projectile (round detonated in middle of range, where center is surrounded by pine boards for measurement of average effective fragment density) 4. At 40' from blast point, Russian 82mm mortar makes 8.3 times the effective hits of U.S. 81mm mortar 5. Russians chose 82mm mortar size because captured 81mm ammo would work in their mortar, but when enemies captured Russian 82mm mortar rounds they would be useless with 81mm mortars. 6. Russian 120mm mortar was described as having "terrifying capabilities" due to the extremely high output of effective fragments 7. Russian mortar and artillery HE rounds have thicker walls and heavier weights of metal than corresponding U.S. ammo, which promotes fragment generation 8. British tests appear to have found that cast iron mortar rounds were more effective at casualty generation

The one advantage of thick armor is that it promotes shot shatter because the thickness is greater than the projectile diameter. If U.S. 76mm APCBC hits Tiger 82mm at a 30 degrees side angle from gun to armor facing, and the round can overpenetrate the armor resistance by 1.05 to 1.25, the round will shatter and fail. Same thing for hits on front of Tiger that should penetrate when penetration is compared to effective armor resistance. We believe that many 57mm L73 hits on Russian front that theoretically should overpenetrate actually failed to defeat the armor because the round self-destructed on the plates. Panther side armor is too thin to generate shatter in most hits. U.S. tests against Tigers at Aberdeen Proving Grounds showed that the armor resistance varied widely, from above average to below average. In addition, the Tiger armor was on the brittle side with very low impact resistance.

The German equation for 30 degree penetration which is identified in the British BIOS report predicts the following figures for subject guns, using best quality ammo that succeeds on five consecutive hits at close to the same velocity: 75L43 APCBC 100m, 97mm 500m, 89mm 1000m, 79mm 1500m, 70mm 2000m, 62mm 88L56 100m, 119mm 500m, 110mm 1000m, 100mm 1500m, 91mm 2000m, 83mm The similarity between the above estimates and the figures in Jentz' Panzertruppen and Chamberlain's Encyclopedia of German Tanks of WW II is notable.

The German equation for 30 degree penetration predicts the following figures for subject guns, using best quality ammo that succeeds on five consecutive hits at close to the same velocity: 75L43 APCBC 100m, 97mm 500m, 89mm 1000m, 79mm 1500m, 70mm 2000m, 62mm 88L56 100m, 119mm 500m, 110mm 1000m, 100mm 1500m, 91mm 2000m, 83mm The similarity between the above estimates and the figures in Jentz' Panzertruppen and Chamberlain's Encyclopedia of German Tanks of WW II is notable.

1.5 inch. .30 cal and .22, respectively. These are basically just redesignated American rounds.</font>

Germans hardened their rounds to 62 Rockwell C at nose, U.S. and Russians used 54.4 and 52. Turns out that harder projectile noses defeat more armor since they transfer energy better and harder noses actually shatter less. U.S. tests for nose hardness effects showed that American or Russian nose hardness could shatter and fail against plates at velocities where German type nose hardness would break up but still defeat armor. German ammo was better, on average. BIOS report shows that cracks appeared in a fair percentage of manufactured ammo, battle reports indicate cases where German 75mm rounds hit targets they usually defeated with ease but the rounds failed to do anything. Sounds like cracks. The Allies tested German ammo during war, we have reports on metal analysis. One of the nine rounds that we have reports on contained cracks. Germans did alot of research on ammo development and production. BIOS report indicates that some German firms produced outstanding ammo with minimum alloys, while others did less well with better materials. Americans had different firms working on ammo, and some of the Chevrolet designs contained soft areas below the nose that would decrease penetration and promote shatter. America turned toaster makers into armor and projectile steel generators. German production ammo seems to be better than U.S., a test with 75mm APCBC ammo from American Sherman and German 75mm PaK had German round outpenetrating U.S. by a good amount. Production quality German 75mm L48 APCBC would penetrate over 100mm of vertical plate at 2030 fps, American Sherman round did 91mm. Part of difference is smaller HE burster in German 75mm ammo (0.2% of weight is burster which is very low), part of reason is harder nose, another factor is better steel.

Germans chose 37mm anti-tank gun size because the overall weight allowed infantry to move gun in desired ways. British 25 pdr was 87.6mm, which rounds to 88mm, if my fading memory still retains some valid recall power. Could someone verify 25 pdr as 87.6mm?

The German equation for 30 degree hits (from vertical) is of the form: velocity in m/s = C' x (diameter in centimetres/weight in kg)raised to 0.5 power x (plate thickness in decimetres)raised to 0.8 power. For 75mm APCBC, C' varies according to following table: Thickness..................C' 80mm......................722 100mm.....................710 120mm.....................690 140mm.....................668 160mm.....................640 180mm.....................628 200mm.....................628 220mm.....................655

You're right, German APCBC ammo was vastly superior to anything the Allies could put together.

The German equation for 30 degree hits (from vertical) is of the form: velocity in m/s = C' x (diameter in centimetres/weight in kg)raised to 0.5 power x (plate thickness in decimetres)raised to 0.8 power. For 75mm APCBC, C' varies according to following table: Thickness..................C' 80mm......................722 100mm.....................710 120mm.....................690 140mm.....................668 160mm.....................640 180mm.....................628 200mm.....................628 220mm.....................655

Quite a few books, including Encyclopedia of German Tanks of WW II and Thomas Jentz' Panzertruppen, have published 30 degree penetration data for German weapons. The basis for the data can be found in the British BIOS report GERMAN STEEL ARMOUR PIERCING PROJECTILES AND THEORY OF PENETRATION, and it provides some interesting twists that are vital to proper use and understanding of the data for APCBC rounds (the thickness penetrated on half the hits should exceed the listed 30 degree figures). 1. German data is based on penetrations with HE burster intact and useful 2. An equation in abovestated BIOS report was used by Germans to estimate penetration at 30 degrees from vertical 3. Estimates are for best quality projectiles (specially made for tests or very best deliveries from standard production), where penetration estimates for average production ammo would require higher velocities to defeat a given thickness according to following figures: a. 5% higher for 75mm b. 3.5% higher for 88mm, 105mm and 128mm projectiles 4. Penetration versus velocity curve for 75mm, 88mm and 105mm projectiles based on obtaining five consecutive hits within a velocity range which result in a success (round passes completely through plate with HE burster intact). 5. The penetration resistance of German plate appears to vary quite a bit as hardness changes 6. The German critical velocity Gd is based on the criteria noted in note 4. above -------------------------------------------------------------------------------------------------------------------- To obtain five consecutive successes within a narrow velocity range as velocity increases, the probability that each round will succeed must be very high. For an 85% probability that five rounds will succeed in a row, the individual shots would each have an average 97% success rate. This means that German data is not comparable to American and British penetration data that uses 50% success as the criteria. To convert the German data to 50% success, the thicknesses would have to be increased by at least 10% (and possibly as high as 15%, subject to standard deviation size), which increases the penetration thicknesses above those shown on the tables even when the decrease to production ammo is considered. With regard to German armor hardnesses, the curves do not reflect the sudden changes in resistance which could occur as plate hardness changes in a step function with thickness variations. BIOS is the British Intelligence Objectives Sub-Committee, and the abovementioned report is BIOS FINAL REPORT No. 1343, ITEM No. 2, dated September 1945. The BIOS mission sent groups to Germany after the war (and maybe during the final stages as key areas were captured), interviewed key German personnel and collected published materials. 30 degree penetration estimates from equation in BIOS report follow for best quality ammo used in tests: 75mm APCBC 146mm at 935 m/s (Panther muzzle velocity) 140mm at 918 m/s (Panther ammo at close to 100m) 100mm at 710 m/s 88mm APCBC 200mm at 1003 m/s (88L71 at 0m) 180mm at 939 m/s 160mm at 886 m/s 140mm at 829 m/s 120mm at 763 m/s (Tiger 88L56 at close to 100m) 100mm at 680 m/s