Thick British AFV Armour

[Guest Germanboy]

Originally posted by Jeff Duquette:

How about a good reference for the Comet? Any suggestions?

From this site: http://wwii-allied-afvs.virtualave.net/ They also have data on the Churchill. You have to be careful with this, I have no way of verifying the data, and just plug it from the net. These are not be-all and end-all statements, rather just some info for the debate.

Armor (mm@degrees)

Front Side Rear Top/Bottom

Hull

64mm@90°(nose) 14mm@90° 25mm@90° n.a.

Superstructure

32mm@17°(glacis) 29mm@90° - 14mm@0°

76mm@90°

Turret

102mm@90° 64mm@90° 57mm@90° 20&25mm@0°

Mantlet 102mm@90° - - -

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Andreas

Der Kessel

Home of „Die Sturmgruppe“; Scenario Design Group for Combat Mission.

[rexford]

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.

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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.

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Note that 20mm was not applied to driver plate, based on AFV Profile info.

[Simon Fox]

Now this thread is taking on the nature of detective story it is starting to intrigue me

Check out this upgunned MkIV (all photos are very useful for this discussion)

http://freespace.virgin.net/chris.shillito/a22new/mk6/ch601.jpg

Rexford wrote

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°.

You are absolutely right. I never looked at the game data before but zero degrees is clearly wrong. The specs I have indicate 25 is the correct angle for the lower hull front. Furthermore only a small part of the front hull is at zero. Above the lower plate is a steeply angled plate ?thickness. The third hull plate is at zero but the co-driver/MG gunners position is protected by a thicker plate which extends across at least 50% of this area. This is the impervious area indicated by the Tiger Fibel.

Andreas wrote

Interesting that the 8th Army undertook those field conversions, if the 6pdr was supposedly better than the 75mm on AT performance. Anyone know the reasoning behind that?

It's only an educated guess but I can think of a couple of possible reasons. Since these were early Churchills it may be that they were armed with the older type 6pdr gun which did not have the same capabilities against armour as the later gun. I am unsure as to how the early gun compares to the 75mm, though the later is clearly superior especially with APDS. Also no HE was available for the 6pdr gun for some time. The conversions may have been performed for this reason.

Jeff wrote

Of course its a MkIV. Thats the point. A large percentage of the Churchills going into ETO 44-45 were MkIV's (see my post above)...or at least that's the impression I'm getting from Fletchers book. A fair number of MkIII's & MkIV are indicated on casualty tables for this time period.

Chamberlain ("British and American Tanks of WWII") seems to imply that the MkVI & MkVII were only armed with the 75mm.

Absolutely right. But a lot of these III's and IV's were 'reworked' and upgraded in various ways. Also the VI designation was used fairly freely to indicate 6pdr versions converted to 75mm.

The existence of official 'kits' for field modification of the Churchill for:

(1) conversion from 6pdr to 75mm

(2) addition of applique armour for earlier versions

definitely confuses the nomenclature of these tanks.

So while we have the factory produced marks there are also various combinations of original vehicle with modification. For example the VII we see in CM could be a factory produced version or a conversion from IV using applique armour and the 75mm gun.

Given the contraversy over the 6pdr/75mm conversion would one also see versions with the applique armour but retaining the 6pdr gun?

Unfortunately our local library service seems to have lost it's copy of The Churchill Tank - The story of Britain's most famous tank, 1939-1965 by Chamberlain & Ellis which would go some way to helping the confusion (and definitely answer Andreas's question too).

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"As has been said, we only listen to bootlickers, and Simon is one of the best out there!"

[rexford]

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.

[Jeff Duquette]

Regarding the 75mm it sounds like around fall of 43 the Deputy Chief of the Imperial General Staff came to the conclusion, based upon interviews apparently, that there was almost unanimous feeling amongst tank crews that the dual-purpose American 75mm was far more desirable than the 6-pdr.

This is kind of a cool construction drawing of the MkVII and MkVIII. From Fletcher's Work again. The thing is to scale...and its pretty evident the sloping along the area of concern. Turret top seems to indicate 20mm plate thickness for the MkVII and VIII.

I havent been able to locate the MkIII or MKIV in the CM armour available to the Brits. Yet from the info posted by GermanBoy the lions share of the Churchills in ETO 44-45 were III's and IV's (a minor gripe at best). I think the sloping frontal armour is of more interest.

[rexford]

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

[:USERNAME:]

Were churchills used on the eastern front? I believe they were. Dos anyone know if the russians put and mods on them? A 76.2 mm field gun would be nice.

Aside from the thrilling posts here, does jeff and rex want the present CMBO churchill changed to reflect this scintillating info? Its hard to tell since BTS isnt part of the discourse.

[Guest Germanboy]

Originally posted by :USERNAME::

Were churchills used on the eastern front? I believe they were. Dos anyone know if the russians put and mods on them? A 76.2 mm field gun would be nice.

Aside from the thrilling posts here, does jeff and rex want the present CMBO churchill changed to reflect this scintillating info? Its hard to tell since BTS isnt part of the discourse.

Yes, but in small numbers (I read of 35 Mk IIIs at Kursk). Don't think they were modded - the Russians thought they were crap to start with.

I do not think that BTS will entertain a code change that incorporates a new vehicle. Madmatt has posted the tweak list in the 'ETA'-thread, no word of it. Steve has categorically stated in a few threads that 1.2 is it and that they will move on to CM2 now.

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Andreas

Der Kessel

Home of „Die Sturmgruppe“; Scenario Design Group for Combat Mission.

[Degrees of Frost]

Originally posted by Jeff Duquette:

..... the whole 6-pdr, 75mm conversion issue. Rather controversial. ....... I thought it had something to do with the superior HE quality of the 75mm.

Given that the Churchill was viewed as an infantry tank the HE benefit was probably given heavier "weighting". Maybe someone knows whether the brits were keen to get more 95mm armed Churchills over the 75mm armed models.

As to the controversy over going with the 75mm over the 6-pounder - I understood this was more of an issue with arming the Cromwells.

[Silencer]

Just a small question of the AVRE mortar and max distance.

http://www.shadowsfolly.com/WWII/Britain/Churchill.htm

--> Fired 40lb bomb 80 yards

CM States max range was 250m???

Does someone has more info on this

S.

[Jeff Duquette]

Degrees of Frost Said: As to the controversy over going with the 75mm over the 6-pounder - I understood this was more of an issue with arming the Cromwells.

It seems to have been the case with the Churchill as well, or so Fletcher indicates. I will post the relevant passages from "Mr. Churchill's Tanks" if there is an interest. I reckon you are probably right regarding the Cromwell. I don't know that much about the Cromwell development, but given the British doctrine of Cruiser Tanks and Infantry Tanks, there would have been a controversy with Cromwell regarding weather the 75mm duel purpose gun or 6-pdr should be employed in the design. When was an HE round for the 6-pdr developed? It's my understanding that Cromwell was designed as a Cruiser, so at least from a purely doctrinal perspective perhaps the 6-pdr was the more desirable weapon.

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On a different tack

One thing I thought was interesting was the Note at the top of that design drawing of the Churchill MkVII and VIII I posted above. If you look at the drawing you'll see a notation indicating IT 80 or IT 90 or the like next to the thickness of plates. These are Izod Test specifications for armour plate. Izod Test is kind of the British Version of the Charpy Test. Izod\Charpy measures toughness of armour plate…the ability of armour plate to absorb energy during the fracture process. Anyway at the top of the construction drawing it reads: "NOTE: Plate material specifications quoted are correct as laid down in the design stage. They are amended from time to time to meet production and supply requirements." This basically gives the contractor\builder an open ended ability to use non-spec plate steel.

One additional point of interest, which might help this discussion along, is what were Toughness Test results for equivalent RHA armour plate for say: German, American or British manufacturers? I guess I would expect FH plate to have lower toughness values than RHA plate. I would also anticipate toughness of German plate to decrease toward the tail end of the war.

[Jeff Duquette]

This is kind of off the beaten track, but speaking of the Charpy Test there was a great deal of Charpy testing conducted on the steel being employed in Liberty Ship hulls during WWII. Apparently Liberty Ships were occasionally literally cracking in half in Arctic seas above Murmansk\Archangel. Lend-lease convoys. It was determined via Charpy testing that the toughness of steel decreases dramatically in sub-zero temperatures. So the normally rather ductile steel being employed in Liberty Ship hulls was failing catastrophically in a brittle failure mode as a result of the cold environment. Steel is moving through the elastic range right to rupture\failure ...very little plastic deformation prior to complete failure. This is a figure from the US Naval Academy detailing reduction of Charpy energy vs. temperature (F = 1.8 x C +32).

So what's my point? I guess I have a question directed toward Rexford regarding extended periods of sub-zero temperatures during Russian Winters and the impact on the toughness of armour plate. You reckon a T34's armour or a MkIV's armour etc was much more brittle in Dec, Jan and Feb on the Russian Front Is tank armour easier to punch through during extended periods of sub-zero temperatures.

[This message has been edited by Jeff Duquette (edited 02-02-2001).]

[Paul Lakowski]

Originally posted by Jeff Duquette:

So what's my point? I guess I have a question directed toward Rexford regarding extended periods of sub-zero temperatures during Russian Winters and the impact on the toughness of armour plate. You reckon a T34's armour or a MkIV's armour etc was much more brittle in Dec, Jan and Feb on the Russian Front Is tank armour easier to punch through during extended periods of sub-zero temperatures.

[This message has been edited by Jeff Duquette (edited 02-02-2001).]

You know I wish I could see the temp gradiant?Yes Temp does play a role.

[Guest Germanboy]

Originally posted by Paul Lakowski:

You know I wish I could see the temp gradiant?Yes Temp does play a role.

Paul, did you at some point in another thread want to see pictures of Stug 75/L48 ammo? I have some drawings that I could scan.

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Andreas

Der Kessel

Home of „Die Sturmgruppe“; Scenario Design Group for Combat Mission.

[rexford]

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.

[Jasper]

"Temp drops would effect projectiles as well as ammo, so ammo nose would be more brittle, too."

Ah hem. I don't know a lot about ballistics physics and the like, but I suspect that if you take something and shoot it out of a cannon - it will exit the cannon slightly warmer than when it entered. I further suspect that as it screams through the air - that friction may warm it up - especially in front. Just a layman's observation.

[Paul Lakowski]

Originally posted by Jasper:

"Temp drops would effect projectiles as well as ammo, so ammo nose would be more brittle, too."

Ah hem. I don't know a lot about ballistics physics and the like, but I suspect that if you take something and shoot it out of a cannon - it will exit the cannon slightly warmer than when it entered. I further suspect that as it screams through the air - that friction may warm it up - especially in front. Just a layman's observation.

Yes but the brittle armor is an issue at cold temp.

[Paul Lakowski]

Originally posted by Germanboy:

Paul, did you at some point in another thread want to see pictures of Stug 75/L48 ammo? I have some drawings that I could scan.

Yes , what I need is cutaway drawings that show the penetrator and nose shape. With measurements would be good but I can live without that for now

I have tons of Russian scale ammo drawings scanned that I can trade....drop me a line.

I also need similar drawings for 75L70 AP ammo.

[Jeff Duquette]

Paul:

The graph is a bit clearer at:

http://web.nps.navy.mil/~me/ms3202/graph.htm

Temp drops would effect projectiles as well as ammo, so ammo nose would be more brittle, too.

The insides of tanks are typically heated via vents and fans running from the engine. Not much different from the heater in your car. So ambient temperature inside the tank where ammo would be stored would be higher than the exterior of the tank. Maybe some WWII tanks didn’t have interior heaters? All the more reason to surrender when it gets cold.

The amount of heat generated by a tanks engine is rather amazing. When a crew beds down for a cold night a choice spot for your fart-sack is the back deck of the tank. The engine will radiate heat for along time through the deck steel...very cozy, other than the hard steel. So the front end of the tank might have a reduction in plate toughness, but the ass end steel plates would perhaps be less affected due to engine heat.

[Paul Lakowski]

AFV Interiors has a new mag up that includes 3 pagers on the Churchill tank, check it out.

http://www.kithobbyist.com/AFVInteriors/church/church1.html

"Turrets for most Churchill tanks were made from welded flat plates, but once again the later vehicle turrets were different, the turret constructed from a one-piece cast unit with steel plates welded to the top for the roof."

Your not going to believe this, but this is the same construction technique in the 1980s modern Challanger -1 tank...well almost.

The turret is a cast construction with Chobham armor applique added over top and hard steel plates confining the whole armor into one element.When it came out in 1985 it was the best protected turret in NATO offering 62cm KE resistance and 100cm HEAT protection.

[rexford]

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.

[Paul Lakowski]

Originally posted by rexford:

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.

Yes imaging fighting at 30 below in the Russian Artic type winters !!