rexford

British tests against 30mm over 30mm on the PzKpfw IIIH, with 37mm thru 75mm guns, shows that the combo resists like a single face-hardened plate with 69mm thickness. American tests against the 30mm over 50mm on the front of PzKpfw IV showed that the combo had more resistance than a single 80mm face-hardened plate. Face-hardened plates in contact resist like more than the total thickness, homogeneous plates in contact resist like less. Here's why. The resistance on the surface of a homogeneous plate is less than the interior because the surface material is not held as tight lyin place by surrounding steel, so it is easier to push aside. With two 40mm homogeneous plates in contact there are four surfaces, whereas a single 80mm homogeneous plate has two surfaces. With face-hardened armor, two 30mm plates in contact present more face-hardened layer thickness than a single 60mm plate, so there is more resistance. Firing tests prove the above theories.

Response to JasonC's comments: "pp 74-76 says with the long 75, fire at enemy AFVs at ranges beyond 1500m was discouraged as ineffective and a waste of ammo, because AP would fail to penetrate even with a hit." Sometimes true. T34 glacis armor thickness varied from 42mm to 55mm, and the shots would certainly bounce off T34 hull fronts carrying 50mm+ armor. Reports in Jentz indicate that the PzKpfw IV with the 75L43 penetrated the T34 at 1600m max range. "p. 84 says the 80mm front models "could withstand the fire of the 76.2mm tank gun of the Russian T-34 if it did not come within 500m." Says the same was true for the ZIS-3. It also mentions a weakness in the gun cradle armor, only 45-50mm (much like the turret of a Pz IV incidentally)." The mantlet around the gun barrel was 50mm thick. The 80mm areas that are sloped at 10 degrees from vertical are small areas with lots of bolt holes, and the driver area has that large cut-out for the driver viser. So edge effects and weak areas abound. The upper superstructure on a StuG IIIG is made up of 50mm plates at 51 degrees slope, which resists 76.2mm hits like 74mm vertical. The 500m penetration of the 76.2mm is 75mm face-hardened, so data matches combat reports. "p. 87 discussing the StuH talks about its weakness vs. enemy armor, because the low muzzle velocity of its HEAT ammo made it effective only at 500m. "At distances under 500m, as was already noted elsewhere, the front armor of the assault gun offered no protection from the fire of tank guns." Could you give us the month and year of the above report. "p. 117 says flatly that the 75L48 with Pz Gr 39 could not penetrate the IS-2 from the front, even at a range of 100m. Nearby, an AAR mentions a StuG killing an IS-2 with its 5th hit after the first 4 bounced, without specifying which plate was struck." Horsefeathers. Why do you believe everything you read without looking at the entire picture yourself. The 75L48 APCBC could penetrate the IS-2 mantlet and turret front beyond 900m if the impact angle were not too large. Look at the data in CMBB. Mantlet and turret front are 110mm and 100mm of high hardness armor, and the armor on the early versions was inferior and prone to flaking. Furthermore, Russian tests with a 76.2mm gun against the IS tank showed that partial penetrations were obtained, and that gun penetrates alot less than the 75L48. The IS tank being fired upon suffered horrendous internal armor flaking within the turret. See the IS development article on the Russian Battlefield site for some more discussion on the 76.2mm firing trials against the IS tank. "p. 127 shows an 80mm front StuG-IV model with track sections on its bow and concrete reinforcements." So what? Face-hardened armor is damaged when it stops a round, and track sections and concrete would reduce the damage to the armor on non-penetrating hits. "Later in the book, the improved effectiveness of the later Allied guns, the US 76mm and the Russian 85mm, is described as their new ability to fight from long range, not needing to close. Not as the first ability to penetrate from the front." We accept that the 76.2mm should penetrate the StuG IIIG front inside 500m. Have you tried to convince the designers that a change to CMBB is warranted?

Based on Russian data, the T34 76mm gun could just barely defeat about 80mm of face-hardened armor at point blank with BR-350B. British firing trials against 30mm/30mm face-hardened with 37mm through 75mm guns (AP and APCBC ammo) suggest that 30mm/50mm face-hardened would resist like more than 80mm single plate. U.S. firing tests against a PzKpfw IVH with 30mm/50mm face-hardened armor show that the combo resisted better than a single 80mm face-hardened plate. JasonC seems to have forgotten my past posts on British and U.S. tests against German combo armor on PzKpfw IIIH and IVH. However,CMBB probably doesn't model the vulnerable parts of the StuG IIIG very well, namely the large 50mm plate that sticks out from the barrel and the thin upper front superstructure plates. The later StuG used a rounded cast mantlet for the gun to avoid the losses associated with the flat 50mm plate, which was an easy penetration. We've gone round and round with Jason C and nothing he mentioned is inconsistent with the 30mm/50mm armor being a tough nut to crack with the T34 76mm gun at all but point blank in CMBB. And we have the stats to support the inability of the BR-350B to penetrate 80mm+ face-hardened at anything but point blank. I would also note that CMBB doesn't give the T34 76mm gun the superhardened 76mm BR-350B round which penetrated about 10% more than the usual version, and there was an uncapped 76mm solid shot AP round which was specially designed to defeat the Tiger side armor. But both rounds (super hard BR-350B and sharp nose AP) were around in limited quantities starting late 1943. [ June 12, 2004, 03:25 PM: Message edited by: rexford ]

Jason C: Very good points. Suggest you bring up the 85mm round break-up problem to the designers and ask why the effectiveness is so low during 1943, and why the round breaks up so much during 1944 and 1945. I'am sure many people would like to see answers to the above issues. Lorrin

Nice response that provided what I was looking for. Thanks so much. Lorrin

Just came across the subject book at the library, and wondered if it had been discussed in the past on this site. The book is written by a U.S. tank gunner with experience in 76mm armed Shermans and the Super-Pershing with added armor and an extra long 90mm gun. The combat situations discussed by the author present some interesting if unusual sounding events, such as multiple battles with King Tigers (one is penetrated through the belly armor when it climbs over an obstacle), 90mm white phosphorus rounds and quite a few frontal hits that are stopped by the added armor. What struck me was the number of close to medium range shots that went over or under their targets, even when the range sounded like it would be less than 200 meters. How did the book stack up against unit histories and combat reports?

Do you think that troops manning a crewed weapon like a machine gun or anti-tank gun, or in a pillbox, would be more difficult to suppress with rifle fire? S.L.A. Marshall found that crewed weapons fired more than individual arms on a percentage of troops basis, and it seemed that they might also stand up to fire better. The question came up because the Russians always fire at the German machine guns in our miniatures games and we felt that MG crews might withstand bullet fire better than a squad. What do you think?

Really great answer John, much appreciated.

Thanks John. What do you think about WRG rules with regard to the inability to kill infantry squads holding in the open or in a trench beyond 25m with a rifle squad or a machine gun? I would really appreciate your views on the above question.

One of the things that gives Fireflies an extra boost in CMBO is the 85% armor quality on the front glacis of a Panther. The game applied one 0.85 quality factor for all rounds, but our work applied a 0.95 multiplier for 17 pdr APCBC hits on the glacis and something similar for APDS. And CMBO does not model the erratic accuracy and failure to penetrate that was often found with WW II APDS (6 and 17 pdr APDS).

If one were to put themselves in the role of a WW II German or Russian riflemen, about how many hits do you think you could score against a man in a trench 150 yards (about 135 meters) who exposed an area of about 0.5 square feet (roughly equivalent to a square with 8.5" sides)? Assume the same kind of rifle used by each side during 1942, and no scope. British calculations result in about one hit in forty shots, while applying the standard British scatter pattern for rifle fire at fully exposed men in the open (90% of shots fall within a 18.6" high x 18.6" box) results in one hit for each five shots against a man in a trench at 150 yards. The British rifle scatter for men in the open might not apply, and may overestimate the chances, if seeing such a small target at 150 yards is a factor as well as men moving in and out of sight inbetween shots. Lorrin

We do alot of miniatures gaming, and often use the WAR GAMES RULES 1925-1950 ruleset. Comparing the effectiveness of machine guns in the ruleset results in the following rankings for shots taken from 100m to 800m: 1. turret coax machine gun 2. German MG34 and MG42, U.S. M1919 3. 12.7mm to 13.2mm heavy machine guns 4. tripod or wheeled light and medium machine guns (Vickers, Browning, M1917, Maxim) 5. bipod mounted light machine guns (Bren, BAR, Russian DP) and bow mounted AFV machine guns What do you think about the above views? How would you compare the effectiveness to the rifle fire generated by a squad, and would you assume that only about 25% of the men in a rifle squad would actually shoot during a firefight? With regard to the unit make-ups, the rulebook indicates that German infantry squads on the Eastern Front would often have two light machine guns (M34) starting 1944, and the rules give German armored infantry platoons two M34 per squad starting 1943, while the motorized infantry have one. Starting 1943, German SS and paratrooper platoons can substitute assault rifles for rifles and SMG. Any comments on the above wargame design?

John Salt's Snippets presents an interesting bit of data on the accuracy of PIAT fire, which is derived from the following report: WO 291/153 Effectiveness of PIAT Shooting The target is a Covenanter tank moving at 10 mph towards, away from and across the line of sight of a PIAT team. First Shot 59% accuracy against crossing target 80% against receding 28% against approaching Second Shot 67% against crosser 79% against receding 42% against approaching Third Shot 55% when target is crossing line of sight 53% when target is moving away 39% when target is heading towards firer In 25% of the hits the DA fuze 425 failed to detonate. The low accuracy against targets moving towards the firer was attributed to nervousness regarding whether a hit could be made in the time that was left. The tank targets were at about 65 to 110 yards range, and with a 10 mph speed it would take from 13 seconds to 22 seconds for an approaching Covenanter to reach the PIAT team from the indicated ranges.

Is it not also the case that the soft, blunt cap reduces riccochets against highly sloped armor? Or was my source just talking through his hat on that one? Michael </font>

John Salt's Snippets can be used to determine the relative constant aim dispersion of 17 pdr APCBC and APDS, and the previous finding that APDS has about twice the scatter is about right. WO 291/238 gives the calculated first shot hit probabilities for several guns and ammo, assuming a 1000 yard target range and a standard error of 250 yards (25% average error, where the assumed errors range from 0% to over 75% and follow a bell-shaped distribution). 17 pdr APCBC is estimated to have a 15% first shot hit chance against a 2' high target, while the APDS is 19%. However, due to the flatter trajectory of APDS compared to APCBC the APDS advantage should be higher. Using the Jurens-Okun trajectory program, the impact of the range estimation error was identified and the 1000 yard standard dispersions were calculated as: 17 pdr APCBC 68% of scatter within 0.43m of aim point 17 pdr APDS 68% of scatter within 0.95m of aim point The random scatter of APDS is about 2.2 times the APCBC figure. Even if 17 pdr APDS was fired at a 2m high target at 1000 yards and the range estimate/gun elevation were perfectly on, about one-third of the shots would miss due to random scatter. The British WO report notes that the wide scatter of 17 pdr APDS makes accurate second shot correction difficult, since the first shot might be based on an accurate range estimate but the wide dispersion could cause a high shot that suggests a long estimate. One interesting note from the WO report is that the service infantry range finder is expected to have a standard range estimate error of 25 yards at 1000 yards, where 68% of the estimates will be equal to or less than 25 yards and 32% will be greater than 25 yards. The average range finder error at 1000 yards is 2.5%, compared to 25% for a man making a visual estimate. There is a large amount of information in John Salt's Snippets and in the Isigny and First Army firing test reports from the Mycenius site which conclusively show that APDS was very erratic in flight and not very accurate.

I accidentally posted on 17 pdr APDS on the wrong forum, please delete. John Salt's Snippets can be used to determine the relative constant aim dispersion of 17 pdr APCBC and APDS, and the previous finding that APDS has about twice the scatter is about right. WO 291/238 gives the calculated first shot hit probabilities for several guns and ammo, assuming a 1000 yard target range and a standard error of 250 yards (25% average error, where the assumed errors range from 0% to over 75% and follow a bell-shaped distribution). 17 pdr APCBC is estimated to have a 15% first shot hit chance against a 2' high target, while the APDS is 19%. However, due to the flatter trajectory of APDS compared to APCBC the APDS advantage should be higher. Using the Jurens-Okun trajectory program, the impact of the range estimation error was identified and the 1000 yard standard dispersions were calculated as: 17 pdr APCBC 68% of scatter within 0.43m of aim point 17 pdr APDS 68% of scatter within 0.95m of aim point The random scatter of APDS is about 2.2 times the APCBC figure. Even if 17 pdr APDS was fired at a 2m high target at 1000 yards and the range estimate/gun elevation were perfectly on, about one-third of the shots would miss due to random scatter. The British WO report notes that the wide scatter of 17 pdr APDS makes accurate second shot correction difficult, since the first shot might be based on an accurate range estimate but the wide dispersion could cause a high shot that suggests a long estimate. One interesting note from the WO report is that the service infantry range finder is expected to have a standard range estimate error of 25 yards at 1000 yards, where 68% of the estimates will be equal to or less than 25 yards and 32% will be greater than 25 yards. The average range finder error at 1000 yards is 2.5%, compared to 25% for a man making a visual estimate. There is a large amount of information in John Salt's Snippets and in the Isigny and First Army firing test reports from the Mycenius site which conclusively show that APDS was very erratic in flight and not very accurate.

The APDS round not only was poor accuracy wise, but the same problem that caused the poor accuracy (uneven shedding of sabot petals) greatly lowered the penetration due to yaw (projectile angle at impact is different from overall flight path or trajectory).

In terms of survivability, the M10 gun shield would resist 50mm and 75mm hits with vertical resistances of 101mm and 95mm, which is somewhat higher than the Sherman mantlet for the 75mm gun when it is treated as one average thickness. In reality, the Sherman mantlet (75mm gun) was curved, and consisted of two thicknesses, with an 51mm cast outer rotor shield spaced over an 89mm cast inner gun shield. While it looks like 140mm total on paper, the combo is spaced, cast, quality deficient and has lots of holes and edge effects. Some time ago we did a detailed analysis of the expected resistance from the Sherman mantlet for the 75mm gun and found that while the average resistance was about 89mm of good quality rolled armor, a wide range of results applied to individual hits depending upon where they landed and the impact angle (mantlet is curved): 8% hit 45mm effective 6% hit 65mm effective 22% hit 75mm 25% hit 85mm 18% hit 95mm 6% hit 105mm 4% hit 115mm 3% hit 125mm 4% hit 145mm 1% hit 155mm 3% hit 165mm Above figures consider impact angle, cast deficiency to rolled armor, armor quality, edge effects, etc. But even on defeated hits, problems could occur for the Sherman since hits that stuck in the outer and innner shield could result in keying, where the gun could not be elevated or depressed due to the stuck projectile.

John Salt's Snippets present the results from two WO reports which show the inferiority of APDS to APCBC ammo in terms of accuracy, and also indicate how much variation in weapon accuracy could be experienced. WO 291/762 deals with 6 pdr firing tests using APCBC (2725 fps muzzle velocity) and APDS ammo (3950 fps muzzle velocity), where the target is a 5' long by 2' high object which represents the Panther turret. The overall hit percentages were (ranges in yards, 5 tanks used in tests): Best 3 Tanks Firing APDS 74% at 500 50% at 800 37% at 1000 20% at 1500 Best 3 Tanks Firing APCBC 89% at 500 84% at 800 81% at 1000 62% at 1500 Worst 2 Tanks firing APCBC 52% at 500 57% at 800 34% at 1000 12% at 1500 Judging from the report stats the tanks initially did not have the range down precisely and started out using an estimate. As might be expected the best shooters with APCBC oudperformed the best APDS trials by a wide margin. What is somewhat unexpected is the large difference between the APCBC firing trials for the best 3 and the worst 2. To obtain the listed hit probabilities at all ranges, the 6 pdr guns would have to be superior to the German 50 L60 APC and 88 L56 APCBC in terms of random scatter with a fixed aim (where those two German rounds had extremely small dispersion with fixed aim). WO 291/1263 presents 17 pdr firing trials with APDS and APCBC where the APDS round is clearly inferior to APCBC: 400 yards 91% for APCBC, 57% for APDS 600 yards 73% for APCBC, 34% for APDS 800 yards 57% for APCBC, 22% for APDS 1000 yards 45% for APCBC, 15% for APDS 1500 yards 25% for APCBC, 7% for APDS In terms of random scatter with fixed aim, the APDS rounds appear to have about twice the dispersion of the APCBC ammo. If some of the APDS rounds performed as designed with small scatter, the average dispersion of the "bad" APDS might be considerably more than twice the APCBC average. The WO report notes that a flank observer could not detect the APDS tracer in 73% of the cases, and in no case was the APDS trace seen from inside the tank. A buttoned-up Firefly would appear to have a difficult time picking up the trace on missed shots with APDS, further decreasing the accuracy of the rounds.

I know it's a subject full of special cases but has anyone seen anything on the average height of WW II infantry, particularly German and Russian?

Thanks for all the helpful responses.

Penetrations by 37mm guns will occur quite a bit in CMBO due to the fairly good penetration at close ranges, but the rounds were small and solid shot so their damage potential is alot less than Sherman 75mm APCBC-HE. The PzKpfw IVH turret front and the Panther side armor are fair game for Stuarts and other pesky little rascals using small guns with high muzzle velocities. CMBO may not penalize 37mm penetrations with solid shot as much as it might. One other point that CMBO may not fully consider is the use of face-hardened armor on the PzKpfw IVH front and the side hull of Panther D's and early A's, which would decrease the penetration (small rounds tend to penetrate alot more homogeneous armor than face-hardened). CMBO was the first game in the series and the combat system has steadily improved over the years.

Going through several sources through the years, there seems to be plenty regarding German conversions of the 76.2mm L51.5 Russian gun (used on early Marders and as an anti-tank gun), but nothing on converted ZIS-3 guns (L41.5). Did the Germans convert any of the shorter barreled L41.5 ZIS-3 Model 42 76.2mm field guns and use them as anti-tank guns? In a slightly related vein, did the Germans fire German made ammo or Russian APBC in the captured T34 tanks that were used by German forces? A few books have German tables of penetration by T34 guns firing German made ammo, which suggests that the Germans may have rebored the T34 guns to take a German made round with much higher homogeneous penetration than the Russian APBC.

One of the peculiarities of Russian penetration range data is that it often ignores great variations in armor slope. Tiger driver plate and nose are same thickness at 9 and 25 degrees slope from vertical, same penetration range is given against both in Russian pamphlet on fighting German heavy tanks. This pamphlet is based on calculations since actual firing trials against a captured Tiger were not yet made when the pamphlet was written. Ferdinand upper side hull and side superstructure is listed as 85mm and angles are 0 and 30 degrees, yet same range is given for 76.2mm APCR. Seems like someone who didn't understand slope effect did the research and wrote the results in both of the above cases, which suggests that neither is based on firing trials. It is possible that the ranges given against the Ferdinand are not penetration ranges but refer to when the target would be considered vulnerable and the first shots should be fired. I don't read Russian so maybe someone can translate what the ranges are supposed to mean.

OnWar site has following armor stats for Ferdinand: Side Hull has 60mm vertical and 80mm vertical Superstructure has 80mm at 30 degrees from vert. Rear Lower hull has 80mm vert. and 80mm at 40 degrees from vert. Superstructure has 80mm at 20 degrees from vert. Russian data appears to show 85mm and 60mm for Ferdinand side armor. Drawing indicates that 76.2mm AP penetrates 80mm/30 degrees at 300m, and 76.2mm APCR penetrates same armor at 300m. 76.2mm AP will not penetrate 80mm/30 degrees at 300m, even if it is pointed nose solid shot round. Russian data suggests 76.2mm APCR will not defeat 80mm/30 degrees at 300m. 45mm APCR penetrates 60mm vertical at 500m (Ferdinand might have 80mm vertical on upper and lower hull side vertical areas, this should be checked). Russian penetration data for 45mm M42 APCR has 80mm vertical at 500m. Ferdinand penetration range drawings appear to show same range for 76.2mm APCR against 80mm vertical (side hull) and 80mm at 30 degrees from vertical (side superstructure), which is a little "iffy", someone forgot the impact of slope effect, which makes a 30 degree slope almost 40% more resistant than same plate at vertical. The Russian penetration range figures look questionable.