rexford

Info on Churchill gun elevation for 6 pdr: http://afvinteriors.hobbyvista.com/church/church2.html Some had shoulder brace elevation for 6 pdr gun, others had elevation wheel, according to article.

Following two sites have some interesting info on Valentine and Crusader. http://afvinteriors.hobbyvista.com/crusader/crus3.html http://afvinteriors.hobbyvista.com/val/val3.html Early Valentine with two man turret and difficult to load 2 pdr gun (see great photo of tight turret confines for two men). 6 pdr guns in both Crusader and Valentine reduced turret crew to two men (expanded Valentine turret allowed three in 2 pdr armed tanks), and 6 pdr elevated by shoulder brace or crutch. Commander was generally the loader in two man turrets, which probably would be much less efficient than the three man crews in PzKpfw III.

The following site has some interesting drawings and photo's of the Matilda II turret interior, including the gunners shoulder harness for main weapon elevation: http://afvinteriors.hobbyvista.com/matilda/matilda2.html The gun sights were marked to 1800 yards, according to the article.

2 pdr gunner with shoulder harness would probably have to raise or lower his shoulders to make it work. CG Erickson sat in a Matilda and I'll ask him about the exact workings.

Robert Livingston provided the following information when I asked him about the Grant gun sight magnification: "I located the source for the 1x note I had written into Hunnicutt. It came from a list we got many years ago from the Bovington Tank Museum, a list of "Most secret" guns/ammo/sights for Brit and US tanks. It clearly says the 75mm gun M2 in the Lee/Grant used an M1 periscope enclosing a M21 telescope with a power of 1x."

The following info was compiled from posts on the Yahoo Tankers site which were contributed by Vasiliy Fofanov, CG Erickson and Bob MacKenzie: 1. German sights such as in PzKpfw III had sight remain stationary while gun elevated, as opposed to Allied and Russian sights. This reduced gunner workload and allowed faster target aim, although German sights were heavier and more complex. German sights were clearer, had higher magnification and a wider field of view for a given magnification. 50mm L42 sight would be much better and more efficient than 2 pdr telescope due to sophistication advantages. Vasiliy Fofanov submitted the following quote which would apply to differences between the simple articulated 2 pdr sight and PzKpfw III: "In order for the light to pass through the elbow of articulated sight, you need several extra lenses there, and of course every new lens reduces the brightness and sharpness of the picture. That Germans managed to produce the "articulated" sights that outperformed "non-articulated" sights of any nation that opposed them is really a fascinating feat of optics engineering." 2. British 2 pdr tanks used shoulder harness on gunner for weapon elevation, which was attached to a friction plate. This was supposed to help when firing on the move (gunner could counter up and down terrain by leaning in opposite direction). I have read where 2 pdr ATG sights were limited to a range under 2500 yards. My opinion is that shoulder harness would not allow fine tuning of gun elevation like a wheel. 2 pdr ATG seemed to have used elevation wheel. 3. Folks will check to see if 6 pdr tanks used shoulder hardness for elevation. 4. I would suspect that German tanks and anti-tank guns would be more accurate than Allied tanks beyond close range due to all the advantages. 5. The 1.0x magnification which we assumed for Grant 75mm based on prior research may have been in error, 1.44x may be more like it. We are looking for our notes from decades ago. U.S. did use 1.0x magnification scopes in Sherman and Stuart until better sights were available (states this in Sherman and Stuart gunnery manual), which may have been basis of our assumption for early Grants and Shermans.

Tom Rodwell posted the following on Yahoo! Tankers site in response to a comment by Vasiliy Fofanov regarding German sight advantages: "The english for "breaking" translation is "articulated" or "hinged" (the latter is more literal) - the advantage is that the gunner can keep his head steady rather than have to move it up and down with the elevation of the gun. The disadvantage is that the sight is much heavier and more complicated to manufacture, requiring more lenses. Only the Germans really had the technological know how to do this at this period of the war without incurring a dramtic loss of either field of vision or magnification. Their sights also had better light gathering properties due to the lens coating and had a wider field of view relative to the magnification than the allied & soviet equivalents. "

Paul Lakowski on the Tankers site posted the following: "Yes my father is an optics expert and was in the german army during the war. He remembered that the zeiss lenses had some gas suspended in the glass that increased clarity and allowed for better field of vision at higher magnifications [when compared to other armies optics]...I think the gas was argon?"

I don't know if the tank and anti-tank gun sights were different with 2 pdr, I've always assumed they were similar since the muzzle velocities are the same. Somewhere I read that the 6 pdr elevation in Valentine tanks was controlled by a harness that fit over the gunner's shoulders, which would not exactly make for the most accurate fine tuning of gun range settings. Hopefully the guy would not have the hiccups. I would appreciate it if someone could check our figures for the early Grant 75mm gun sight, 1.0x magnification seems awfully low. We have ARMORED FORCE FIELD MANUAL on Tank Gunnery, dated April 22, 1943, and the following magnification factors are given for Sherman and Stuart tanks: Sherman M3 75mm gun =================== Telescope M38 with periscope M4 1.5x magnification "The linkage arm connecting the periscopic sight to the elevating mechanism may get out of adjustment. the linkage is adjusted only by ordnance maintenanc e personnel." Telescope M32 with Persicope M3 1.0x magnification "This sight is used with the 75mm gun M3 in Medium tanks of the M4 series. The periscope M3 is substitute standard and will be used only until the periscope M4 is available." German sights also have exceptional light gathering characteristics so would be able to pick up targets at sunrise, sunset, in the rain or through dust and fog better than Allied sights. There is a story somewhere about a Tiger that blew apart a T34 formation in a fog, where the Tiger could see the T34's but the Russian tanks could not pick up the origin of the deadly accurate fire. The Americans in Europe noted that German sights worked better in low light conditions and during overcasts. [ September 21, 2003, 09:03 PM: Message edited by: rexford ]

Pages 84 and 85 in our book, WW II BALLISTICS: Armor and Gunnery, give gun sight magnification and field of sight figures for a variety of tanks and guns. Of interest are: M2 gun on early Grants and Lee (75mm L31) ========================================= 1.00x magnification, 11 degree field of view and uses roof top periscope that is vulnerable to linkage misalignment Not especially good on long shots due to no magnification, very limited field of view 37mm gun on early Grants and Lee uses periscope alongside gun with same characteristics as 75mm sight M3 gun on Early Lee and Shermans (75mm L40) =========================================== 1.44x magnification, 9 degree field of view is VERY limited, uses roof top periscope that is vulnerable to linkage mis-alignment. 37mm uses same sight type as M3 gun 2 pdr ===== 1.9x magnification, 21 degree field of view range marks limited to under 2000 yards (read where an Australian aimed at a fleeing armored car at over 2200 yards by guessing where the range mark would have been, and hit the car on the first try). 50mm Pak ========= 3.0x magnification with 8 degree field of view, it is said that when 50mm Pak reached the desert combat ranges suddenly increased by a significant amound. PzKpfw III and IV ================== 2.5x magnification amd 25 degree field of view 50mm L42 may have lower velocity than 2 pdr but gun sight magnification is almost one third higher. 88mm Flak ========= 5.0x magnification with 8 degree field of view

Thanks for all the responses. APCR for 6 pdr would have called: Armor Piercing Composite Non-Rigid (APCNR) APCR and HVAP contain a tungsten core penetrator in a lightweight carrier, and the whole thing travels to the target. APDS is Armor Piercing Discarding Sabot, where the tungsten core penetrator travels to the target but the light weight carrier falls off just after the round exits the gun barrel. The problem with APDS may be due to the discarding sabot, where it is supposed to fall off in three pieces (?) but if one lags a little it throws off the inflight stabiity by introducing a wicked yaw (projectile nose is pointing away from the direction of travel). In British and American tests with 17 pdr APDS it would penetrate at a given impact velocity and then fail at a much higher velocity, which could be due to inflight instability (or could be due to tungsten shatter gap).

I've seen some penetration range stuff for the 85mm Flak versus the Tiger from Russian sources. The 88mm L56 gun that Rommel used so effectively was a flak, and that gun had plenty of APCBC and some APCR. The Russians had 76.2mm and 85mm flak guns and both of them fired armor piercing rounds.

Did the British ever shoot 6 pdr APCR in Africa or anywhere during the war? John Salt's compilation of penetration stats shows an April '43 Ministry of Supply memo with penetration data for 6 and 17 pdr APCR ammo at 30 degrees from vertical. I have never seen any reference to British APCR outside of the John Salt find.

Redid the calculations, summarized results. 80mm/55 degrees with 0.915m height and 3m width uses 0.442 cubic meters of steel 202mm vertical with same height and width plus 20mm hull top plate at 20mm uses 0.638 cubic meters. Above analysis does not include side plates, where sloped armor uses 50% less side armor within nose area. Trade-off is 50% less internal volume with 80mm/55 degrees within nose area compared to 202mm vertical.

One of the advantages of sloped armor is the slope effect, where the effective resistance is much greater than the horizontal distance that must be pierced. When an 80mm plate is angled at 55 degrees from vertical, the horizontal distance across the angled plate equals 80mm/cosine(55 degrees), or 139.5mm. However, when 17 pdr APCBC strikes the 80mm plate at 55 degrees from vertical the effective resistance is the same as a 202mm vertical plate. Say the 80mm plate at 55 degrees must cover a vertical distance of 0.915m and a lateral distance of 3m. The total volume of sloped plate to provide 202mm vertical resistance would equal: 0.080m x 0.915m/cosine(55 degrees) x 3m = 0.383 cubic meters. If a 202mm vertical plate were used the volume of that plate would equal: 0.202m x 3m x 0.915m = 0.554 cubic meters. But with a vertical plate a hull top plate must then be added to cover a 1.60 meter distance, which adds: 1.60m x 3m x 0.020m (hull top thickness) = 0.096m So, to get 202mm vertical equivalent resistance, 80mm at 55 degrees from vertical uses 0.383 cubic meters of armor plate while a 202mm vertical plate requires 0.650 cubic meters (70% more than the 55 degree case). Sloped plate allows high resistance to penetration with a decrease in weight, which is why it was used on Panther, Pershing, King Tiger, etc. IMPORTANT NOTE Projectiles do NOT penetrate sloped armor by moving through it horizontally. The first reaction during penetration is a tendency of the round to rotate nose up and start to ricochet. While the rotation is going on a plug is formed which starts to be driven out. The projectile then changes direction suddenly and pierces the plate going DOWNWARD, with the nose bouncing against the hole and it moves thru. There is alot going on and that is why 80mm/55 degrees resists like 202mm vertical instead fo 139.5mm vertical.

If a T34/85 fights a Tiger head on at 100m, hits on the mantlet will do nothing. Hits on the front lower hull, where the armor is 102mm thick and angled at 24 degrees, will have a so-so penetration probability since the penetration is only a little bit greater than the effective armor resistance. The failures at 100m probably occurred because the hits failed to strike the driver plate (102mm at 10 degrees from vertical), or hit the front lower hull and were unlucky (probably hit a track link which added 5 extra millimeters, just enough to stop the hit).

JasonC posted: "A T-34/85 on the other hand should kill through any aspect and plate at close range, *except* the turret front. That is modeled as 100mm "reinforced turret front", which is practice usually means something ridiculous like 200mm aka M-1 APFSDS is supposed to bounce. Other than that only high side angle should hurt you, or extreme range (by CMBB standards) from the front. In pratice I find 85mm in CMBB needs close flank shots just to punch through 80mm armor (with occasional partials vs. Tiger I front hulls or Panther front turrets)." Hogwash. Just played a scenario where three regular Tigers lined up against five T34/85 during June 1944 on flat open terrain, after 60 seconds two Tigers penetrated and knocked out on front upper hull hits. Four T34/85 knocked out, one T34/85 penetrated but still kicking. Tiger mantlet, which is what the reinforced turret front refers to, is much thicker than the T34/85 AP penetration (120mm at 100m) during June 1944. Tiger mantlet is 135mm directly around gun, then is 140mm to 150mm thick on the slightly depressed flat areas. Hits on the upper and lower areas, where the thickness varies from 100mm to 125mm, are backed up by a space and then a 100mm plate. Our current penetration figures for 85mm ammo have: AP rounds 142mm at 100m, 135mm at 250m, 125mm at 500m APBC rounds 139mm at 100m, 133mm at 250m, 123mm at 500m CMBB has lower figures for 85mm AP and APBC.

The following net site offers an interesting summary of how climate and weather influences sound waves: http://www.ourhealdsburg.com/noise/outdoor_sound_transmission.htm If one stands on the end of an active aircraft runway and faces into the wind, they may not hear an oncoming aircraft due to the bending up of the sound waves. [ September 02, 2003, 08:52 PM: Message edited by: rexford ]

Based on research with noise impacts from auto traffic: 1. winds above a certain speed tend to bend sound waves upwards, and turbulence has the same effect 2. sound seems to carry better in winter (made noise readings for aircraft landing at the local air carrier airport during summer and winter) 3. low vegetation tends to absorb sound waves and reduce noise impacts For wind effects on ballistic accuracy, the lateral impact on first shots can be substantial but is a function of range. Second and follow-up shots usually include corrections for lateral error (jump, trunnion cant, wind, etc) so steady wind is an initial but not continued problem. Gusts are another matter. The Americans published analyses of crosswind effects on 75mm, 76mm and 90mm APCBC during WW II: LATERAL DRIFT DUE TO 10 MPH CROSSWIND (16.1 kpH) 75mm APCBC fired at 619 m/s 0.55m lateral drift at 915m 2.20m lateral drift at 1829m 4.66m lateral drift at 2744m 3"/76mm APCBC fired at 793 m/s 0.46m at 915m 1.83m at 1829m 4.53m at 2744m for 3" APCBC 4.09m at 2744m for 76mm APCBC 90mm APCBC fired at 814 m/s 0.32m at 915m 1.35m at 1829m 3.13m at 2744m 90mm APCBC fired at 854 m/s 0.24m at 915m 0.99m at 1829m 2.25m at 2744m The lateral drift due to other factors varies but is a fairly good percentage of wind effects.

I've also read about early morning fog in the desert. Fog is generally created when the temperature drops to the dew point of the air, and the morning temp in the desert can be really low. There are alot of small creatures in a desert that live on early morning dew. The lowest daily temperature occurs just after sun rise, when the earth is losing heat faster than the oblique sun rays can add heat. Advanced Squad Leader has something on desert fog if my memory cells are still functioning.

"For the rest of the speculators, understand that the standard models all predict marginally *lower* performance from layered plate, not higher. That is why battleships aren't layer cakes. The typical effectiveness for the weight can be as low as .85 times a single plate for 2 of equal thickness." But are the standard models for homogeneous or face-hardened armor? And, naval face-hardened armor is MUCH DIFFERENT than tank face-hardened armor. With Naval face-hardened armor, the resistance is less than with homogeneous armor at high impact angles from plate perpendicular, but the opposite is the case when U.S. APCBC is fired against both types of tank armor. Naval and tank armor have different face-hardening depths and characteristics so one can't use the standard naval models for layered armor with FHA. We need actual firing test results against tank face-hardened armor that state the impact angles and are based on 50% success. I also restate somethings from a previous posting that is pertinent and needs to be kept in mind: 1. the driver plates on a StuG III are bolted and are relatively small areas, so edge effects come into play and will reduce the effective resistance 2. German face-hardened plates were not face-hardened around the edges, so if the total area of a plate is small the homogeneous areas make up a greater percentage (and these are the areas that suffer from edge effects). 3. hits on the front of a StuG III have a chance of hitting the upper superstructure than the driver plates, where the resistance could allow 500m penetrations by 76.2mm APBC. 4. 500m could be the range where a high percentage of frontal hits land on the 50mm face-hardened gun mantlet I do not believe that there is a direct relationship between 500m penetration vulnerability and the resistance of the 30mm/50mm driver plates, cause there are other areas that are more likely to be hit inside 500m.

"Unless the explanation is tied to face hardening and layering combined, it will give incoherent or false predictions. Note that caps are usually considered the solution to face hardening, and everyone agrees uncapped AP underperforms against the plates in question." Well, with layered armor the first face-hardened plate destroys the armor piercing cap, and then a capless projectile hits the second face-hardened plate. So one could speculate that two face-hardened plates are better than one (by the way, the total face-hardened layer thickness with 30mm/50mm is greater than the thickness with a single 80mm face-hardened plate). Anyway, Miles Krogfus has some microfiche with German firing test data against layered armor and he is researching the material. Perhaps we will soon have something substantial and supported in depth.

Some time ago Miles Krogfus shared a number of British Ordnance Board graphs with me for German 50mm APC, 75mm very small capacity HE APCBC and 88mm APCBC with small and large HE capacity. Going back over the graphs after estimating the vertical penetration of 75mm and 88mm ammo from trials at 45 and 55 degrees, the graphs are in close agreement with the estimates from oblique hits: VERTICAL PENETRATION ESTIMATES 75mm small capacity APCBC at 750 m/s (PzKpfw IVH muzzle velocity) 137mm from oblique hit 140mm from British O.B. curve 88mm small capacity APCBC at 780 m/s (Tiger muzzle velocity) 157mm from oblique hits 157mm from British O.B. curve 88mm large capacity APCBC at 780 m/s (Tiger muzzle velocity) 141mm from oblique hits 138mm from British O.B. curve 88mm small capacity APCBC at 1000 m/s (Tiger II muzzle velocity) 224mm from oblique hits 220mm from British O.B. curve ========================== 50mm APC at 2240 fps (PzKpfw IIIG muzzle velocity) 76mm from British O.B. curve 50mm APC at 2700 fps (PzKPfw IIIL muzzle velocity) 99mm from British O.B. curve The consistency of the British Ordnance Board curves with the estimates from oblique hits suggests that the O.B. curves may have been based on firing tests.

Some time ago Miles Krogfus shared a number of British Ordnance Board graphs with me for German 50mm APC, 75mm very small capacity HE APCBC and 88mm APCBC with small and large HE capacity. Going back over the graphs after estimating the vertical penetration of 75mm and 88mm ammo from trials at 45 and 55 degrees, the graphs are in close agreement with the estimates from oblique hits: VERTICAL PENETRATION ESTIMATES 75mm small capacity APCBC at 750 m/s (PzKpfw IVH muzzle velocity) 137mm from oblique hit 140mm from British O.B. curve 88mm small capacity APCBC at 780 m/s (Tiger muzzle velocity) 157mm from oblique hits 157mm from British O.B. curve 88mm large capacity APCBC at 780 m/s (Tiger muzzle velocity) 141mm from oblique hits 138mm from British O.B. curve 88mm small capacity APCBC at 1000 m/s (Tiger II muzzle velocity) 224mm from oblique hits 220mm from British O.B. curve ========================== 50mm APC at 2240 fps (PzKpfw IIIG muzzle velocity) 76mm from British O.B. curve 50mm APC at 2700 fps (PzKPfw IIIL muzzle velocity) 99mm from British O.B. curve The consistency of the British Ordnance Board curves with the estimates from oblique hits suggests that the O.B. curves may have been based on firing tests.

The British report indicates that at 45 and 55 degrees impact, none of the German rounds penetrated in a condition where the HE burster would work. So, at high angles the German HE filled ammo was just like a solid shot except for the loss of penetration and added work that the HE filler entailed.