rexford

The hit percentage I referred to in first post was prior to start of action, as tanks used line of sight to potential targets. No dust, no rain, no movement, tanks at an angle to each other so target width something larger than head-on shots. In other words, optimum shot conditions. Before BTS closes book on CM they should look over all of the data because there are slope multipliers that go up as thickness goes down, which is opposite of how things work. Our armor penetration booklet is close to finished and we have been using it to go over alot of what is in CM. Not saying we're 100% correct, just identifying things BTS might like to examine one more time. The booklet has been refined over 25 years and mistakes have been weeded out. If BTS looks into Will Phelps' PzKpfw IV web site and buys the copy of AFV G2 with Mark Diehl's article on German ammo that is advertised there, they will see that 75L24 HE has more amadol than Panther 75mm. They will also see some questionable data. The hit percentage difference between elite and average crews should exceed 10% if elite has 10% average range estimation error and average has 25%. Our beef with CM is that hit percentages are not based on trajectories and range estimation errors but a "feel" for what is correct. Intuitive "feel" without analysis based on trajectories seems too speculative, and the differences between 75L40 and 88L71 ammo or elite and poor crews would be a shot in the dark. With trajectory analysis one can say average crews will use a 25% range error and the resulting difference between 75L40 and 88L71 is such and such. The Eisenhower report presents one complaint after another about how the Panther and Tiger II guns have flat trajectories and better sights and hit alot more often at long range than 75mm Shermans. Yes, one can go on forever about this stuff and we'll leave the subject. However, prior to leaving subject forever, who can avoid the PARTING SHOT What about the intuitive "feel" for APDS accuracy, which is described by Jentz as not particularly accurate and firing test results show to be erratic in terms of accuracy AND penetration. If APDS round is thrown off course by sabot pieces staying on too long, penetration falls off due to yaw. Where is the CM "feel" for APDS inconsistencies? And CM "feel" for Panther glacis flaws where some tanks are good, some are poor, but all are penalized in game. And "feel" for other Panther armor areas where there is no proof that the nose and side were as inconsistent in quality as glacis. And "feel" for HE fire at ground point targets, who would ever think that 75L24 HE (420 m/s) would be more accurate than 88L56 HE (810 m/s) against ground point targets (my original conclusion is correct after rereading German ballistic tables). Or that 75L24 HE would contain more explosive than Panther 75mm HE (look it up in Diehl, 30% more amadol in short 75 HE). Or that guns firing at target points above the barrel are more accurate than guns firing down. My point is that it takes analysis and calculations to model things in a game so odd and unexpected results can be included. Without trajectory analysis all of the little weird things go unnoticed. Without shatter gap, German armor gets zonked when American tanks wiht 76mm guns should be mince meat. But it isn't a one way street, it takes analysis and "feel" to make a game.

Hard armor on outside of Crusader, softer steel on inside. Layered armor on Crusader performs well, according to stories.

The max hit probability thread seemed to post examples where hit probabilities were higher than 65% at 550m. Men might not be robots but using reasonable error ranges for range estimation, and reasonable shot scatter due to mis-aim, gun sight problems and so on, that 88L71 should hit on more than 2/3 of first shots at 550m. At 550m, Jagd Panther 88L71 trajectory is so flat that many errors can be made and round will still hit a large target like a Sherman. If gun is aimed at 200m range, it hits Sherman. With 900m aim, it still hits Sherman. That means that range estimate and gun setting from 200m thru 900m hits Sherman at 550m most of time. So range estimate can be in error by over 60% against 550m target and still hit with 88L71. It also seemed that 75L48 accuracy was close to 88L71 against 550m target. Will check closer on this since 88L71 should be more forgiving on aim error than 75L48. Average range estimate error from studies is 25%. Will look into issue and see if hard combat data exists. Thanks for posts.

Oops! Right about tank interior and heating up through barrel. Was thinking about anti-tank gunners pulling rounds out of a frozen box. Advantage would seem to go to projectiles during dead of winter. My mistake. But wouldn't gun barrel contract more than tank projectile in cold, possibly leading to slower muzzle velocity. Since penetration tests are conducted at nice comfy temps it is a great point was previously made that penetration and armor calcs wouldn't strictly hold up in real deep cold. Eye opening point.

In last night's game, first shot by Jagd Panther against a Sherman in the open with flat ground had 63% hit probability at 550m. This seems low when trajectory analysis is completed with 25% range estimation error. Seems like it should be closer to 90%. Has anyone played games where first shot accuracy between 500m and 600m is well above 65%?

Jentz book on North Africa has some penetration ranges vs. Italian tanks including M13/40, and comparison of penetration at range to armor thickness identifies a horde of possible shatter gap cases. All shots and penetration data at 30 degrees to armor. 1. Hull front superstructure, 1300 yards penetration is 35, armor is 30 at 11 degree 2. Mantlet, 600 yards penetration is 49, armor is 37 round 3. Hull front, 800 yards penetration is 45, armor is 30 round 4. Turret side, 1400 yards penetration is 33, armor is 25mm at 22 degrees 5. Hull and Superstructure side, 1600 yards penetration is 30, armor is 25mm vertical Since Italian armor was very brittle, and penetrations would normally kill the entire crew due to flying armor fragments, it is not likely that Italian armor had quality factors above 1.00. This suggests that 2 pounder penetration range was actually somewhat greater than the tests. If above test results are picking up point where penetration is 25% greater than armor resistance, and hits just beyond beyond that range fail due to shatter gap failure, the following shatter gap ranges could be presented (30 degree lateral hit angle): 1. Hull Front Superstructure 2 pounder AP penetrates to 1300 yards, fails to about 1600 yards, penetrates to 1700 yards Armor quality about 0.93 2. Mantlet penetrates to 600 yards, fails to 1000 yards, penetrates to 1100 yards Armor quality is 0.94 3. Hull Side penetrates to 1600 yards, fails to 1850 yards, penetrates to 2050 yards armor quality is 0.96 --------------------------------------- 2 pounder AP against front hull of M13/40, zero degree lateral angle penetrates to 1600 yards fails to 1900 yards penetrates to 2000 yards Above analysis assumes that 2 pounder follows same shatter fail pattern as U.S. 76mm APCBC. ------------------------------------ If 2 pounder AP were firing at 30+30 front plate on PzKpfw IV with zero lateral angle, it would penetrate to 300 yards, fail to 550 yards, and penetrate out to 660 yards, based on U.S. 76mm APCBC pattern. From 300 to 550 yards would be the "shatter gap" where "should be" penetrations would result in shattered failures. If a gamer knew the shatter gap real well, they could close with PzKpfw IV to the 300-550 yard range and fight from there. It's good to know things better than the actual tankers (although German tankers might have noticed that killing hits were bouncing for some odd reason, the British certainly noticed).

Titanic sunk because of brittle fracture. Liberty ships sank by themselves due to square openings in deck that created stress concentrations, and once a crack started it kept on going. Some WW II tanks, may have been Churchill, switched from square to round exit hatches to reduce penetration resistance losses around square edges of opening. Temp drops would effect projectiles as well as ammo, so ammo nose would be more brittle, too. T34 armor is already brittle, Churchill armor may suffer more because it is more ductile to start with. But since Churchill armor is thicker, T34 may lose more resistance due to T/D. If CM is going to say goodbye to CM without addressing new found Churchill armor issues, it would be sad. 89+89+13 on driver plate is one heck of a thick proposition to model with 88mm game armor.

Paul, Re-checked WW II tests where 40mm AP fired at two plates in contact, impact angle is 30 degrees. Two plates in contact at 30 degrees are 11% more resistant than a single plate of same overall thickness hit at 30 degrees. Same result in both cases. So the result you noted in an earlier post, that plates in contact at an angle react differently from vertical case, appears to apply to WW II steel ammo. This suggests that 89+89+13 around Churchill MG port is one heck of a tough target with any kind of lateral angle.

Found British Brinell Hardness figures and used National Physics Lab equation to predict loss in penetration resistance as plate thickens above 2.5". For 152mm plate and cast, quality factors are: 1.00 against 50mm hits 0.95 against 75mm hits 0.93 against 88mm hits 0.88 against 128mm hits This is for unflawed armor. For 88mm plate or cast: 0.98 vs. 50mm hits 0.96 vs. 75mm hits 0.95 vs. 88mm hits 0.94 vs. 128mm hits

Found some WW II tests for 40mm AP against two plates in contact, 30 degree impact. Two plates in contact resisted with 8% less resistance than a single plate with same overall thickness. Bovington provided penetration data for German guns at 30 degree impact, with following figures for Panther 75: 30 degree penetration 100 yards-141mm 1000 yards-121mm 0 degree penetration (estimated) 0 yards-190mm 100 yards-186mm 1000 yards-157mm Above figures are what we use for Panther 75 penetration. Following British data appears to be actual test data since weight of armor driven out of plate is given: --------------------------------------- 88L56 APCBC-HE 500 yards 30 degrees-114mm 0 degrees-148mm (my estimate) 1000 yards 30 degrees-106mm 0 degrees-136mm (my estimate) 1500 yards 30 degrees-97mm 0 degrees-123mm (my estimate) 0 yards 0 degrees-163mm (my estimate) ----------------------------------- 88mm Flak 41 500 yards 30 degrees-159mm 0 degrees-210mm (my estimate) 1000 yards 30 degrees-149mm 0 degrees-195mm (my estimate) 1500 yards 30 degrees-139mm 0 degrees-181mm (my estimate) 0 yards 0 degrees-226mm (my estimate) A DeMarre estimate for 0m penetration of 88 Flak 41 from 88L56 yields 234mm, which is close to 226mm (3.5% difference).

Previous post was for homogeneous armor. Against face-hardened 75mm M61 penetrates 2.5" at 30° at 1710 fps, and 1.25" at 30° at 1060 fps. 1604 fps penetrates both 1.25" at 30° spaced face-hardened plates 50% of time, which is equivalent to a single face-hardened 2.25" plate at 30°. So one 2.5" face-hardened plate at 30° is 11% more resistant than two 1.25" face-hardened spaced plates hit at 30°. When round went thru first plate at 30° it probably would be turned towards the second plate, so 30° impact on first spaced plate and less than 30° on second, so a single plate hit at an angle is even more resistant than previously calculated. There is little available data on plates in contact hit at an angle, and this really is an important issue. Crusader had sandwich armor with a very hard plate underneath, and it is said that the armor performed better than a single plate of lower max hardness. With face-hardened armor the hard layer is on the outside, Crusader carried hard layer on inside. When armor is hit at 0° and 40°, two different types of failure would be active. Against near vertical armmor, projectile may penetrate plates in contact by pushing nose through armor. As nose pushes through first plate, there is less resistance to pushing armor away from line of travel since back-up plate does not apply shear stresses as first plate moves outward. This is theory behind concept that homogeneous plates in contact are less resistant. On 40° hits, plate defeat by plugging. Projectile hits first plate and tries to push a plug downward, second plate resists plug movement. It is possible that on angled hits plates in contact are better than one plate with same overall thickness. This needs further research.

Paul, Data from TM-9-1907 At 1850 fps, 75mm M61 penetrates 2.5" at 30° 50% of time. At 1100 fps, 75mm M61 penetrates 1.25" at 30° 50% of time. If 75mm M61 strikes first 1.25" @ 30° and penetrates 100% of time, and then continues on and penetrates second 1.25" @ 30° half the time, the required velocity is 1665 fps. So two spaced 1.25" @ 30° plates have an equivalent single plate resistance of 2.17" at 30° (this is penetrated at 1665 fps). A single 2.5" plate at 30° offers 15% more resistance than two 1.25" spaced plates hit at 30°. Germans put spare tracks on a target and calculated resistance at three angles. At low impact tracks lowered resistance, at intermediate tracks did nothing and at steep angle the tracks added. This may mean that at low angles tracks did not add full thickness to resistance, and at steep angles track addition to resistance was greater than track thickness. Will look deeper into plates in contact hit at angle.

Analysis uses the curves in TM-9-1907, and we'll asume HE burster is not working and APCap remains undamaged on round. This will simplify analysis and make it easier to follow. Find the velocity needed by 75mm M61 to penetrate a single 40mm plate at 0° on half the hits, assume 1142 fps (don't have my TM nearby). Then assume that a second 40mm plate is spaced behind the first, requiring 1142 fps. Impact on first plate must have sufficient kinetic energy to pierce first plate 100% of time and then defeat second plate 50% of time. 100% penetration requires about 20% more penetration than 50% defeat, and 14% higher velocity. Velocity needed to defeat both plates is then (based on kinetic energy analysis): ((1.14 x 1142)^2 + (1142)^2)^.5, or 1732 fps. 75 M61 penetration at 1732 fps is about 73mm. The problem can be solved in other ways, and yields the same answer. We have factors that modify results for AP nose blunting on first plate and loss of APCap, which actually may increase penetration against second plate (haven't finished calculations yet). Going backwards, what single plate thickness is the same as a 40mm and 53mm plate spaced apart. (1297^2 + 1390^2)^.5 = 1901 fps 75 M61 penetrates about 83mm at 1901. Spaced plates are easier to penetrate than a single plate of same total thickness because DeMarre equation has kinetic energy changing as plate thickness to 1.4 power. Make the plates half as thick as 80mm and it requires 38% as much energy to penetrate 40mm as 80mm. Two times energy for one 40mm plate is 76% of energy needed to defeat 80mm. The reason is due to plugging failure versus push aside, where plugging takes less energy than a round that must fight through the entire thickness. When 75mm hits a 40mm plate, the round overmatches the armor thickness and failure tends to be by a plug of armor failing around the perimeter and then driving out in one piece. This is low energy failure. When 75mm round hits 80mm plate, there is enough material to prevent plugging and the round must push through against continuous resistance, which takes alot of energy. One 80mm plate takes more energy to defeat than two 40mm. Looked at another way, if one has a 1' thick wall and a 2' thick wall, the work needed to knock a hole in the thicker wall will be more than twice what is needed against 1'. The thinner wall may fail by having an entire piece give way around the edges while the thicker wall may only fail by pushing out a small hole. Thin plates fail by punching out whole pieces, thick plates by drilling a hole. Simplistic explanation but that is why spaced plates generally aren't as good against WW II steel ammo (unless first plate detonates round or blunts the sharp nose, or removes APCap so face-hardened can break up nose). If tungsten shatters or cracks against an outer plate, which is possible since the projectile is very brittle, the second spaced plate may be sufficient to stop the pieces. High hardness and brittle behavior often go together, like ceramic armor that can defeat hits but is then in pretty bad shape. Alternating layers of hard and soft material may serve to break-up a projectile against hard armor, and then soft armor absorbs fragment energy by deflecting. Modern armor is not my best subject so excuse me if I exaggerate or make an error. Merkava uses alot of armor tricks to defeat rounds, and it is not clear if alternating hard/soft layers or open spaces would help against WW II steel projectiles. At Shoeburyness the U.S. HE detonators may have fizzled alot, but spaces would help detonate some rounds inbetween armor plates.

WW II steel projectiles are different than modern ammo. It can be shown using penetration curves in TM-9-1907 that two spaced 40mm plates don't equal 80mm single plate resistance if round doesn't detonate. Merkava has spaced hull armor? Long thin penetrators or tungsten behave differently from steel AP or APCBC. In fact, if two parallel plates are hit at 45° to outer plate, the initial plate will turn the round towards the second plate so that the impact angle on the inner plate is alot less than 45°. Alot less resistance than a single plate, especially since slope effects are function of T/D (armor thickness/projectile diameter) and two single plates offer alot less sloped resistance than one plate. Nathan Okun has done alot on this subject regarding WW II naval penetrations. When PzKpfw IIIN spaced armor didn't detonate round, it wasn't that good. However it would blunt sharp nose AP rounds so penetration against inner plate dropped.

KV tanks fought during 1941 do not appear to have face-hardened armor, since 50mm rounds that hit them were reported to dig into armor and then rebound without leaving a dent. Face-hardened armor defeats hits by shattering the projectile nose, softer cast and rolled homogeneous armor (RHA) by deflecting and absorbing energy. British tested KV-1 tank and it was either homogeneous armor in 240-290 Brinell Hardness range (machineable quality), or homogeneous hard on add-on pieces (like extra plates added to driver plate, nose and side turret protection). Soviets generally used high hardness for armor used on faster tanks and homogeneous machineable quality for tanks designed to take hits and trade blows. High hardness good against rounds smaller than armor thickness, like 37mm gun against T34 side. U-boats reported to have used face-hardened armor on conning tower to help defeat hits by aircraft cannon. All those PzKpfw III's, and alot of IV's, in North Africa were loaded with face-hardened armor. British thought Tiger had face-hardened armor when 6 pounder hits shattered. It was shatter gap failure when rounds that should have penetrated failed against Tiger 80mm plates. 80mm face-hardened German armor would have less resistance than rolled homogeneous against Sherman 75mm APCBC, but would perform better than homogeneous against uncapped 75mm AP. Our penetration data for U.S. ammo will show this when the booklet is released. The armor penetration booklet is about 85% complete and will primarily present results with enough explanation to use the curves and data. Tank armor data will indicate thickness, slope, flaw tendency and what type it was (cast, face-hardened, high-hardness, etc.). Data will also identify spaced and plates-in-contact armor areas and text will present equations that explain how to convert spaced or contact plate armor to an equivalent single plate thickness. Two 40mm plates that are spaced resist like a single plate with 72mm thickness, as a starting point. However, capped rounds and uncapped rounds adjust the equivalent thickness and rounds with HE bursters may detonate in the space as they leave the first plate. We're trying to simplify how these things are handled. Not a simple thing, spaced plates or plates in contact. The intent of the armor booklet is to present basic data to analyze and predict penetration ranges and probability. There is alot of data out there that does not address all guns, all ammo types or all armor types. We have compiled information and estimated figures to fill in missing data. Available equations were used to estimate after alot of cross-checking data for other guns to be sure the equations worked reasonably well for other cases. The booklet won't be 100% accurate or totally consistent with published sources, but should be the best single document available. CM armor penetration analysis is based on many of the curves that will be presented in the booklet.

Responding to previous posts: Face-hardened slope effects are similar to RHA and vary with T/D ratio German armor has advantages that CM should model, and disadvantages. We prepared the original flaw equations that found their way into CM through armor quality multipliers, and Panther glacis is major weak area. About half the Panthers carried alot of face-hardened armor, we wonder if this is in CM. A list of CM panzers with face-hardened armor would be interesting. Face-hardened armor will be a big plus on Eastern Front where Russians did not use armor piercing capped rounds. Allies using APCaps on most or all rounds by 1944, face-hardened not so good. Since face-hardened armor is more sensitive to projectile size than RHA, and face-hardened penetration falls off slower with velocity changes than RHA penetration, big rounds on Eastern Front (85,100,122,152) not good for face-hardened panzers. Face-hardened penetration falls off with velocity raised to 1.25 power, RHA variation is velocity raised to 1.428 power. Face-hardened penetration dependent on projectile diameter to 1.25 power, while RHA is diameter to 1.0714 power. If projectile diameter increases from 75mm to 122mm, RHA penetration increases by 68.4% while face-hardened pen. increases by 83%. U.S. face-hardened penetration curves in TM-9-1907 show reduced penetration at high velocities by 76, and lower pen. at all velocities by 57 and 90. These effects do not show up with RHA. Americans fired captured German 75mm against RHA and face-hardened armor, German 75 outdid U.S. 75mm against RHA but was the same against face-hardened. You just can't predict some things. To be realistic a game should catch all of the little things that make tanks good and/or bad. Germans had alot of advantages that CM may not use in all cases, and panzers had weaknesses. We try to be fair and unbiased, and have promoted some allied tank advantages. Churchill tanks with 88mm frontal armor are being promoted on "my" thick British armor thread. Front armor was 89+13 around driver hatch on front (it isn't 88mm armor, it's 89mm), and an incredible 89+89+13 around hull MG. And nose was at 20° slope. And 38mm at 70° glacis, which significantly exceeds 88mm at 0° resistance. CM has none of this from what we can see. We have design drawings and specs for Churchill tanks and CM understates armor resistance. Churchills were harder to defeat than CM portrays, although they could still be knocked-out fairly easily, but a more difficult target than a Sherman. British tankers complained bitterly about how easily Churchills were being penetrated in France. We're saying Churchills are better than CM portrays while still having major weak areas.

Finding the proper armor resistance is like a detective story. Finding the correct answer for CM is the goal. The driver/hull MG plate is over 190mm total thickness, counting two 89mm plates over 13mm inner thickness. That's over half the vertical plate (AFV Profile shows a Churchill where the vertical plate is at 20° from vertical). The steeply sloped glacis on the "88mm" armor Churchills is 38mm thick and is at 70° from vertical, that's an effective resistance of over 120mm vertical plate. Churchill VII has 57mm at 70° glacis. CM underestimates Churchill frontal resistance, and their data does not match pictures and drawings of the tank. The AFV Profile drawings clearly show two thick plates covering the hull MG port, and the design drawings show an additional 13mm under alot of the armor. It appears that CM took the commonly quoted 88mm figure for Churchill armor and applied it. AFV Profile and British design drawings for Churchill IV-VI show that 20mm applique was added to front nose and first half of side armor. That earlier Churchills were converted to Churchill VII equivalents that had: 89+20 on nose at 20° (I measured this angle from design drawing T.D. 5912) 88 and 191 on driver/hull MG vertical plate 38 at 70° glacis Churchill VII turret with 152mm front half side armor of 76+20 Above analysis doesn't consider that plates in contact resist with less than total thickness. We need to gather enough info so that the game armor will be revised and the change will be correct.

The Mark IV-VI Churchill armor protecting the center and right side of the vertical driver plate consisted of 3 plates in contact (thanks to Jeff Duquette for info): 89 + 89 + 13 = 191mm total This is consistent with Tiger Fibel. Even with reductions for plates in contact being less than a single plate of same total thickness, an 88 hit on the area around the hull MG would probably bounce at point blank. This may explain the point blank defeat of the 88 hit in North Africa best, if Mark III was similar. AFV Profile 1 on Churchills show a line of tanks during April 1945, and the first tank appears to have a 20° slope to the vertical driver plate. Maybe the color paining or drawing in the center of the profile, which represents a sloped vertical plate, is accurate but was taken from a model that was a small portion of total production (maybe from one factory). Agreed that early Churchill armor does not have 100% relevance to later marks. The reference was to show that British armor could possess weaknesses despite naval excellence. ----------------------------------------- CM appears to grossly underestimate Churchill Mark III-VI armor: driver plate with 102-191 total thickness, 20° on front nose not 0°, 20mm applique applied to front nose and front of side armor, etc. The Churchill Mark III-VI armor in CM really needs to be re-examined and revised ASAP. ------------------------------------------ Note that 20mm was not applied to driver plate, based on AFV Profile info.

Closely examined the Churchill drawings in AFV Profile 1, and CM may have messed up Churchill armor. Nose is 88 @ 20°, CM has 88 @ 0°. Although driver plate is normally assumed to be vertical, AFV Profile drawing shows driver and MG plates at 20° from vertical. This is an important issue that should be resolved, since it may underestimate resistance by more than 10%. In addition, there is an added 72mm plate that protects around the MG, if this is on top of 88mm front plate the total protection would be 160mm prior to reductions for plates in contact and edge effects. Tiger Fibel showed an area on Churchill front hull that could not be penetrated by Tiger 88 at any range with 30° shot, and this is same area where AFV Profile shows added 72mm armor. So, 88 Flak bouncer at point blank may have hit 72mm on top of 88mm, which would surely stress the round and may bring out any inherent defects. It is always good to take another close look at tank armor, if only to check CM for little oversights.

With regard to British factories getting better at tank armor, NPL equation appears to be based on late WW II armor and projectiles, and thick armor loses resistance when the NPL equation is used to predict penetration. And the NPL equation predicts that British high hardness armor falls apart when overmatched at an angle, where similar German and Soviet plate hit under the same circumstances loses resistance but still puts up a decent fight. We have looked at this question for a long time and believe, but aren't totally sure, that thick armor on British tanks did not harden properly in many cases and lost resistance. The NPL equation is consistent with thick armor that loses resistance compared to 2.5" plate. Throw flaws into the mix and things get worse. This is why it is so important to examine actual penetration cases. The 88 bouncing off 88mm Churchill armor at point blank is a valid situation, the round penetrates about 160mm at point blank. Why would it bounce? Cracked projectile, soft ammo and shatter gap, any number of other factors. What we need is penetration ranges where projectile penetration can be compared to armor thickness and a rough quality factor can be determined. If 152mm Churchill frontal armor is penetrated by 75L46 at range and angle where penetration is 129mm at 0°, quality multiplier can be determined. This would answer question as to whether 6" armor is deficient. If other penetration ranges are consistent then we can say that a trend appears to exist, and quality might be estimated a little better.

Two plates in contact resist with less resistance than a single plate of same total thickness. British NPL suggests that when 152mm British is hit by 75mm rounds (undermatching), the armor does not resist like a scaled up 64mm plate but loses resistance. This may be due to difficulties involved in hardening thicker armor. We ran the NPL equation for 152mm armor hit by 50mm rounds, and in that case 6" armor was equivalent to a scaled up 64mm plate (same quality factor). But 75mm hits on 6" British armor take advantage of whatever hardening deficiencies existed even though the armor is very thick relative to projectile diameter. And the NPL results are probably against unflawed armor, so flaws might further reduce the resistance. If Churchill had 88mm base armor of uneven quality plus added 64mm (decent hardening, possible flaws), the result might be equal to a 152mm plate due to resistance loses when plates are in contact. Equations generated by Nathan Okun predict that 64mm in contact with 88mm resists like a single 133mm plate. If the 88mm plate is bad, the resulting resistance is less. Robert Livingston has discussed German ammo quality control quite a bit, very few rounds were actually inspected and noses were welded onto the projectile body. In quite a few cases, German ammo was seen bouncing off targets that should have been penetrated. Germans also admitted that rounds could have cracks. A bad ammo lot, or soft rounds, could explain alot. North African Churchill has 88mm driver plate and 88mm cast turret front, 88mm L56 APCBC from Flak penetrates about 140mm at 500 yards and 122mm at 1000 yards, based on Mark Diehl's data (which may be American estimates from firing tests and DeMarre equation use). Does 88mm Churchill armor with great ductility, no flaws and excellent hardening wave off hits from 88L56 inside 1000 yards on the basis of quality alone? Probably not. Battle reports also suggest that 88mm Flak ammo used early in the war may have been softer than the 61 Rockwell C average hardness of rounds captured in Europe. Didn't 88 hits on KV tanks seem to bounce alot during 1941? Some of these soft rounds may have been used in the late stages of North Africa out of necessity. Soft ammo is also prone to shatter gap failure.

The Eisenhower report noted in an earlier post on this thread was read (thanks for address), and Tigers are also noted as having better soft ground movement than Shermans. Royal Tigers compared to Shermans over soft ground and Tiger II sunk in less than Sherman. Ground pressure is one thing, and uniform pressure is another. Tiger II has more wheels, larger wheels and more wheel locations and has to have more uniform ground pressure than Sherman. If the Ike report is believed, Shermans with six wheel locations, made up of small wheels, would appear to have a higher PEAK ground point pressure than Tiger II.

If 88mm armor on Churchill is poor early in war, before mass production dilutes alloys, one might suspect that 152mm later in war would be as bad, if not worse. Interesting speculation. NPL equation predicts that 152mm at 220 Brinell Hardness would resist 75mm hits like 137mm of good rolled armor, and resist 88 hits like 132mm: alot less than CM predicts.

If 88mm Churchill armor is sub-par, the question might be asked if 152mm would be better given alloy shortages and mass production demands later in war. The NPL equation predicts that 152mm of British armor at 220 Brinell Hardness would resist 75mm hits like 137mm of good rolled armor, and would resist 88mm hits like 132mm. This is alot less than CM predicts (95% x 152mm = `144mm of good rolled armor).

British NPL equation predicts that 152mm of British armor at 220 Brinell Hardness will resist like 137mm of good quality rolled armor (250 Brinell Hardness) against 75mm hits, and 132mm against 88 hits. This is alot less than 95% factor used in CM.