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Old February 17th, 2023, 08:12 AM

Charles M Charles M is offline
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Default Sloped armour calculations

If I have any serious misgivings about the accuracy of any features of the game it concerns the hull front armour factors of vehicles with sloping glacis plates for the T-34 family, the later JS2, the Lee / Grant, Sherman family, Pershing Panther and Jagdpanther, Tiger II and similar vehicles.

Let us take the Panther family as a specific example. The slope calculator gives an effective thickness of just 139mm for a plate 80mm thick sloped at 55 degrees to the vertical. As Panther / Jagdpanther glacis plates were often 82mm or 85mm thick, the equivalent figures are 143mm and 149mm. This corresponds to drawing a horizontal line through the sloped plate and takes absolutely no account of the slope's deflective qualities, in keeping with old poorly-researched wargame rules written in the 1970s. This reasoning grossly underestimates the value of sloped armour. The true value, allowing for slope, is over 180mm, though in fairness the protection value would be slightly different for each different calibre and type type of projectile striking it. Steel Panthers seems to have partly cribbed the excellent system used in ASL as devised by Lorrin Bird, but with some glaring blunders. In ASL the Lee / Grant and early Sherman were given a hull AF (armour factor) of 8 to reflect the fact that the glacis armour was made up of a number of pieces initially rivetted and later welded together. The T-34 and later Shermans with 47 degree hull fronts were given AF 11 as these plates were stronger one-piece structures and therefore more resilient. The 6 AF for the Lee / Grant in SPWW2 is too low and should also be 8 to reflect the deflective quaity of the plate.

In ASL the Panther family's hull front factor AF is 18, equivalent to over 175mm of vertical plate,and superior to the Churchill VII's 14 AF, which was based on a vertical plate 152mm thick. In ASL the graph produced in R.M Ogorkiewicz's Design and Development of Fighting Vehicles, Macdonald, London, 1968, p. 83 was used, which shows the difference between "actual" (your 139mm) and "effective" protection. (ASL's 18 AF) value. A plate set at 35 degrees, on this graph, gives 1.75 times the thickness as "actual", in other words a horizontal path through it, or 140mm. The equivalents for 82mm and 85mm plates are, respectively, 143.5mm and 148.75mm. The "effective" thickness would vary according to the type and calibre of the projectile, and to some extent also on the quality of the plate. German plate declined in quality during the war years as non-ferrous ingredients were increasingly unavailable, so that reliance had to be made on carbon as a hardener (making welding difficult and prone to brittleness) and a heating then quenching process that often resulted in flaws being produced in the plates. This issue is addressed in Bird and Livingstone, and a number of Osprey Publications in the Duel series draw on their research.

Returning to Ogorkiewicz's graph, the "effective" thickness for a plate angled at 55 degrees to the vertical is 2.8 times more than a 80mm plate or 224mm, for a 82mm plate 229.6mm, and for a 85mm plate 238mm. These values represent "best case" situations, and to allow for the many variables that could occur in real life, in ASL a mid-point between the two curves on Ogorkiewicz's graph was used, i.e., 2.275. This gives effective Panther / Jagdpanther armour of 182mm, 186.5mm and 193.37mm for 80mm, 82mm and 85mm plates, respectively. These values are borne out by the accounts of the difficulty allied weapons had in penetrating the glacis plates of Panthers and Jagdpanthers, even allowing for the poorer quality plates to crack. All my sources, consulted over more than fifty years of my research bear this out. For example, Bird and Livingstone estimate that Soviet 85mm APCR would penetrate about 175mm of armour at 100 metres; giving the 85mm weapon a chance of penetrating the Panther / Jagdpanther glacis plate at close range, but if the 14 AF value in Steel Panthers is used, the 85mm would be expected to penetrate out to about 400 metres, which is nonsense. The Army Museum in Warsaw has lower nose plates from Panther / Jagdpanther hulls with 85mm piercing cores partially penetrated and stuck ("keyed") in the plates, but significantly no upper glacis plates on display. The nose plates varied from 60-75mm depending on when built. This suggests that glacis plate penetration was by no means guaranteed, even at close range.

Incidentally, in light of the above the 100mm glacis plate of the game's Panther II, Unit No. 191, should be around 22 AF, rather than the paltry 17 given, and the Königstiger and Jagdtiger about 30.

I suggest that you rework all the sloped armour factors for vehicles with glacis plates like the Panther and T-34 families, or simply use the values in ASL. For space reasons I cannot list them all here but am happy to assist further if you wish.

Sources

Lorrin Rexford Bird & Robert D. Livingstone, World War Two Ballistics: Armor and Gunnery, Overmatch Press, NY and Connecticut, 2001 2nd Ed.

David R. Higgins, Jagdpanther vs SU-100, Osprey Dual # 58, Osprey Publishing Ltd, Oxford, 2014

Peter Chamberlain & Hilary L. Doyle, Encyclopedia of German Tanks of World War Two, Arms & Armour Press, London, 1978

Steven J. Zaloga & Jim Kinnear, T-34/85 Medium Tank 1944-94, Osprey Vanguard # 20, Osprey Publishing Ltd, Oxford, 1996
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Old February 18th, 2023, 08:55 AM
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Default Re: Sloped armour calculations

The armour slope calculator is a simple mathematical tool that measures the horizontal distance between two points of a slope. Any number higher or lower than that is INCORRECT.

The game then throws a range of variables into the penetration ability of any given AP round out to max distance and that determines if the armour is penetrated or not
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