Bismarck/Tirpitz = most powerfull European battleships

Discussions about the history of the ship, technical details, etc.
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tommy303
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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby tommy303 » Mon Sep 27, 2010 7:13 pm

Didn't a 1600lb AP bomb at about 300m/s velocity and an angle of impact of about 70° penetrate the 50+100mm arrangement on Tirpitz?


It appears one did, but was a dud. Had the fuze functioned properly it is likely the bomb would have burst on the Panzerdeck without getting through it.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby lwd » Mon Sep 27, 2010 7:20 pm

tommy303 wrote:
Didn't a 1600lb AP bomb at about 300m/s velocity and an angle of impact of about 70° penetrate the 50+100mm arrangement on Tirpitz?


It appears one did, but was a dud. Had the fuze functioned properly it is likely the bomb would have burst on the Panzerdeck without getting through it.

Why is that? If it made it intact with a fuze malfunction the only reason I can see that it wouldn't have made it with a fully functional one is if the delay was such that it detonated before it got there.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby tommy303 » Mon Sep 27, 2010 7:29 pm

Which is precisely what happened with the other AP bobm hits that went through the upper deck--they were detonated before the bombs made it to the Panzerdeck.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby JtD » Mon Sep 27, 2010 8:09 pm

Other ones were dropped in a different attack, probably from a lower altitude that simply prevented them from penetrating. A fuse can get damaged by the impact, Bismarcks shell that hit PoW below the waterline was possibly defused upon hitting the water.

I'd count the bomb as defeated, even though the armour was defeated as well. ;)

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby dunmunro » Mon Sep 27, 2010 8:15 pm

tommy303 wrote:
Didn't a 1600lb AP bomb at about 300m/s velocity and an angle of impact of about 70° penetrate the 50+100mm arrangement on Tirpitz?


It appears one did, but was a dud. Had the fuze functioned properly it is likely the bomb would have burst on the Panzerdeck without getting through it.


How many 1600lb hits were there? IIRC, most of the hits were 500lb bombs, which were not intended to penetrate the MAD.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby Dave Saxton » Mon Sep 27, 2010 11:53 pm

Thorsten Wahl wrote:
lwd wrote:I noticed in the file gsap_088 (part of the zip package linked by Thorsten) it states something to the effect that a plate thickness of .2 D required to decap a projectile. Now some latter infromation shows that this is very conservative but it implies that the the deck if it was designed to decap was designed to decap 250mm and over the magazines only 400mm projectiles. Rather brings to question whether or not decapping was the purpose.


0.2 D in the line of flight if i understand the meaning right
so 50 mm thickness at 60° obliquity should be equivalent to 100 mm in flight direction


--------------------------------------------------------------
against 1600 lbs AP bombs at 300m/s and 20° obliquity no existing horizontal protection scheme should be able to defeat such a piece


Indeed, the striking angle is most important to most of these discussions. I looked up some data today , rather than trust my increasingly feable memory :oops: , on the required decapping plate thickness per the striking angle. It appears that ~13% D (50mm for a 38cm) by the point of 30* obliquity is relative to 26% D at the normal. But there was much more that I had forgotten. Another factor is kenetic energy. It was found that with higher levels of kenetic energy, that slightly less thickness was required to effect de-capping. Next the material strength and hardness of the de-capping plate mattered. It needed to be armour grade material for the 20% D rule, or much more was required. Another factor was the caliber radius of the projectile's head as previously mentioned. An additional factor was the interspace distance. If the interspace was close, then much more was required to insure de-capping. APP30 mentions that it was found that the great interspace distance of the Tirpitz type arrays would mean that a capped projectile would be de-capped by the time it reached the panzer deck. In the British test arrays the interspace was always very small, well less than 1 caliber for a large caliber shell. It is thought that this was a primary factor in inconsistent results. But overall the amount of de-capping plate thickness required was mostly a function of the relative striking angle.

A 1600lb projectile, only 20* from the normal, and at 300 M/s, can defeat more than 200mm of both types of armour according to the curves. Cemented armour would probably be better against a projectile striking that close to the normal.

The British commented that a spaced array should be constructed with a cemented main plate if the typical striking obliquity is less than 30* -40* from the normal, but this proves counter productive against more accutelty oblique striking angles, and for more accutely oblique striking angles a spaced array should use homogenous armour instead. Indeed the US Nat Lab tests that yielded +100% effective thickness used RHA throughout, as these test were for accutely oblique striking angles. RHA is used mostly today anyway. Most of the British 1940's era test arrays were for face plates or belts in mind, and so used cemented resistance plates. One series of vintage British tests investigating which armour type was better for a spaced array deck system, provided no comparable data, because the test arrays which used cemented, and thoses which used homogenous resistance plates, both rejected the projectiles.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby Dave Saxton » Tue Sep 28, 2010 12:14 am

dunmunro wrote:
tommy303 wrote:
Didn't a 1600lb AP bomb at about 300m/s velocity and an angle of impact of about 70° penetrate the 50+100mm arrangement on Tirpitz?


It appears one did, but was a dud. Had the fuze functioned properly it is likely the bomb would have burst on the Panzerdeck without getting through it.


How many 1600lb hits were there? IIRC, most of the hits were 500lb bombs, which were not intended to penetrate the MAD.

In the April attack there were 4 direct hits with 1600lb AP bombs. There was one hit in the final August attack that was also a dud. My source says it penetrated 5 decks totaling 150mm of steel coming to rest on the "platform deck".
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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby JtD » Tue Sep 28, 2010 6:55 am

The 300m/s and 70° are a very high assumption from my side, since they imply ridiculously high release altitudes. US bomb charts give penetration 7" of STS for these parameters. The dedicated dive bomb chart ends at 5" for 5000' release altitude (which is practical).

I would like to know which curves you were using, Dave. Mine are from "Terminal Ballistic Data" of the "Office of the Chief of Ordnance", September 1945.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby Dave Saxton » Wed Sep 29, 2010 2:03 pm

70* turns out to be a good estimate as this was the typical dive angle at the time of release for the Barracuda and increasing from there. The bomb came to rest in the number four switch board room with the case broken. This area was protected by 50mm + 80mm, not 50mm + 100mm.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby JtD » Wed Sep 29, 2010 3:01 pm

300m/s are high, though.

According to Dulin/Garzke, the bomb hit the switch board room in compartment XV, which was protected by 50+100mm.

What's your source?

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby Serg » Wed Sep 29, 2010 3:44 pm

Tarrant/Last year of Kriegsmarine p135: "One 1600lb bomb hit on the port side of the bridge superstructure, penetrate five decks of total thickness of 5.8 inches, and come to rest in No4 switchboard room on the lower platform deck, but failed to explode." So, the one source for 50+80 :-)

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby JtD » Wed Sep 29, 2010 4:02 pm

But switchboard room 4 is in compartment XV, not XIV, isn't it?

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby Herr Nilsson » Wed Sep 29, 2010 4:57 pm

Only over the main armament magazines the armor deck was 100 mm in that compartment.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby alecsandros » Wed Sep 29, 2010 5:43 pm

Herr Nilsson wrote:Only over the main armament magazines the armor deck was 100 mm in that compartment.


Maybe some authors included the battery deck (20mm St52, situated 2.4m beneath the upper deck) in their description ? Even if the St52 isn't fully armor grade, it is stronger than usual construction steel of the time and, in most depictions of Tirpitz's horizontal protection, it appears as an "armored deck" or "protected deck".

This would explain the descrepancy between 130mm and 150mm, I think...
Last edited by alecsandros on Wed Sep 29, 2010 6:23 pm, edited 1 time in total.

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Re: Bismarck/Tirpitz = most powerfull European battleships

Postby JtD » Wed Sep 29, 2010 6:10 pm

Herr Nilsson wrote:Only over the main armament magazines the armor deck was 100 mm in that compartment.


I've read a statement like that in the specification for the construction - do you know a better source, in particular plans like general arrangement and armour distribution (original sources) for more than the 4 cross sections one can find in every other book?


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