British postwar tests on armor

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Alberto Virtuani
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Re: British postwar tests on armor

Post by Alberto Virtuani » Sun Apr 28, 2019 10:02 pm

Hello everybody,

according to M.J.Whitley (German Capital Ships of WWII, pag.177 and 178), who cites the subsequent investigation, the bomb struck the Gneisenau at 23:15 on February 26, 1942. The bomb penetrated the upper deck and the battery deck, was deflected by the longitudinal armored bulkhead at frame 185.6 and exploded against the main armored deck in the seaman petty officers' mess.

The MAD was not penetrated (just distorted by the force of the explosion), but it was established that a hatch had been left open, allowing hot splinters to penetrate the vitals, rupturing fuel tanks and generating gases that caused a second huge explosion 25 minutes later (it was initially thought it could have been a second bomb from another air raid).

This second explosion, happened within the vitals, ignited and blew up the 28cm charges in the "A" turret main magazine. Ammunition had not been disembarked, as per German usual procedure before docking, in order to speed up the emergency repairs after Cerberus, to leave the exposed Kiel and to proceed asap to the safer Gotenhafen.
Damage control parties were able at least to flood the magazines of "B" turret (as well as the reserve magazine of "A" turret and all the shell rooms), "limiting" in some way the damages, that did not prevent Gneisenau from reaching Gotenhafen under her own power.


Alec is right, it wasn't a failure of the armored system, but of on board discipline (a hatch left open) and of by-passed safety procedures (docking the ship with ammunition still on board) that ended the operative career of Gneisenau.


Bye, Alberto
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Re: British postwar tests on armor

Post by dunmunro » Mon Apr 29, 2019 3:51 am

This is from Whitley:
...The bomb struck and penetrated the upper deck forward of "A" turret and was deflected aft by the longitudinal armoured bulkhead at frame space 185,6, subsequently exploding on the armoured deck by a hatch and ventilation trunk, in the seaman petty officers' mess. The vertical bulkhead was ruptured and fire spread to the forward crew space through this hole, but the bomb did not penetrate the armoured deck. This was distorted by the force of the explosion. However, the hatch to the 28 cm magazine is believed to have been open (it could not subsequently be found) and the flash and splinters entered the magazine...
So we don't actually know that the magazine hatch was open but the whole sequence of events is strange. What is certain is that the 2in weather deck was cleanly penetrated.

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Re: British postwar tests on armor

Post by alecsandros » Mon Apr 29, 2019 5:44 am

Thanks Alberto,
It's what I remember as well (only that I thought the first explosion took place against the weather deck).

Best,

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Re: British postwar tests on armor

Post by paul.mercer » Mon Apr 29, 2019 9:19 am

HMSVF wrote:
Sun Apr 28, 2019 8:08 pm
paul.mercer wrote:
Sun Apr 28, 2019 4:41 pm
spicmart wrote:
Fri Apr 26, 2019 9:37 pm


You don't count the 2 inch upper deck of Tirpitz in?
Gentlemen,
Just an aside, but does this mean that the two 'Nelsons' were actually pretty tough old birds
Yes, very tough, although their armoured belts were reckoned to be on the shallow side. This was identified and a planned modification was prepared but never fitted due to the onset of war. My understanding was that they employed the basics of the aborted G3 and N3 designs. They were certainly a quantum leap on previous British battleships. What they lacked (and the G3's had) was speed.


Best wishes


HMSVF
Hi HMSVF,
Many thanks for your reply.
I seem to recall that somewhere in a previous post a couple of years ago (I think) I asked what the difference was between a 1 ton bomb and a 1 ton shell hitting a battleship.I'm writing from memory, but as far as I recall the answer was that the bomb was more likely to penetrate the armoured deck than a shell.So are we saying that in the battle with Bismarck, her 1 ton shells would not be capable of penetrating Rodney's armoured deck?

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Re: British postwar tests on armor

Post by paul.mercer » Mon Apr 29, 2019 9:20 am

Double post again, think I'll have to cut off my 'mouse' finger!!

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Re: British postwar tests on armor

Post by HMSVF » Mon Apr 29, 2019 1:08 pm

paul.mercer wrote:
Mon Apr 29, 2019 9:19 am
HMSVF wrote:
Sun Apr 28, 2019 8:08 pm
paul.mercer wrote:
Sun Apr 28, 2019 4:41 pm


Gentlemen,
Just an aside, but does this mean that the two 'Nelsons' were actually pretty tough old birds
Yes, very tough, although their armoured belts were reckoned to be on the shallow side. This was identified and a planned modification was prepared but never fitted due to the onset of war. My understanding was that they employed the basics of the aborted G3 and N3 designs. They were certainly a quantum leap on previous British battleships. What they lacked (and the G3's had) was speed.


Best wishes


HMSVF
Hi HMSVF,
Many thanks for your reply.
I seem to recall that somewhere in a previous post a couple of years ago (I think) I asked what the difference was between a 1 ton bomb and a 1 ton shell hitting a battleship.I'm writing from memory, but as far as I recall the answer was that the bomb was more likely to penetrate the armoured deck than a shell.So are we saying that in the battle with Bismarck, her 1 ton shells would not be capable of penetrating Rodney's armoured deck?
That is definitely a question for Mr Bill Jurens!

In my own head I think it would depend on the angle of fall of the shell,it’s velocity and weight. I assume that it harder for the shell than the bomb. In my own head - just as tanks have sloped armour to increase the thickness of plate a shell firing on a flat trajectory, an armoured deck means that the shell has to penetrate more plate at a shallowish angle than if it fell straight down vertically.

But that’s just my simple guess! Bill Jurens is the recognised master and will give you the answer I’m sure! I’m just a muppet who likes naval history!

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Re: British postwar tests on armor

Post by Dave Saxton » Mon Apr 29, 2019 2:45 pm

HMSVF wrote:
Mon Apr 29, 2019 1:08 pm


In my own head I think it would depend on the angle of fall of the shell,it’s velocity and weight. I assume that it harder for the shell than the bomb. In my own head - just as tanks have sloped armour to increase the thickness of plate a shell firing on a flat trajectory, an armoured deck means that the shell has to penetrate more plate at a shallowish angle than if it fell straight down vertically.
Bombs can strike decks at or close to the normal. The normal being striking at a right angle. This is what makes bombs a more dangerous threat than long range shell fire.

Battleship deck armor effective thickness is determined based on Immunity Zone calculations. For example, if the IZ is to be from 20,000 meters to 30,000 meters against a certain gun, then the effective thickness of the deck protection should be at least the amount of effective thickness that the gun in question can penetrate at 30,000 meters. Such a shell will strike about 60 to 55 degrees from the normal at that range. So a bomb that can strike at or near the normal presents a very dangerous threat indeed.

The reason bombs from bombers needed to be released from 5,000 feet(Bomber Command determined 7,000 feet) or higher was so the bomb could develop enough impact velocity. Velocity is by far the more important factor to the striking energy compared to the weight. The striking energy is the weight divided in two multiplied by the velocity squared.

In most cases, given the technology of WWII bombing, level bombers flying at more than 5,000 feet altitude had little chance of scoring a hit on even a stationary ship. This is why the dive bomber became the preferred delivery platform. Dive bombers proved effective against such heavily armoured warships as the Musashi.

Another bombing technology that could be accurate enough against armoured warships was guided bombs.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: British postwar tests on armor

Post by Bill Jurens » Mon Apr 29, 2019 4:41 pm

The situation is complex, but it may take me a day or so to properly elaborate. It would be helpful if those interested might supply fairly specific situations to be explored, as the variations which occur in a general situation are so great as to obscure basic principles. So, one needs to compare shell with characteristics "A" against bomb with characteristics "B" against target with characteristics "C". Unless A, B, and C are fairly well defined, generalization is difficult, and the results may vary.

That being said, in general, projectiles will deliver more kinetic energy and are, because of their relatively low explosive payload compared to bombs, better penetrators. When bombing accuracy was poor, it was often felt that large-payload bombs exploding in 'near miss' situations could be more damaging than direct hits that penetrated armor. And, of course, if aircraft were involved there was also often a feeling that a ton of torpedo represented a better tactical weapon than a ton of bomb...

Guided bombs represent a different issue, not because of the properties inherent to the weapon itself, but due to the fact that the percentage of hits then tends to be much higher. In general a relatively poor penetrator hitting (say) half the time is better than a good penetrator that hits only 10% of the time.

Mr. Saxton made a small error, stating that "The striking energy is the weight divided in two multiplied by the velocity squared. " If I interpret his phrasing correctly, this makes the striking energy as (M/2) *( V^2). It's actually half the product of the the weight vs the velocity squared, i.e. (M * V^2)/2.

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Re: British postwar tests on armor

Post by Bill Jurens » Tue Apr 30, 2019 1:54 am

H have now had a bit of time to consider the question in more detail. Unfortunately I remain unable to proceed without knowing more about the conditions under which comparison might be made.

Mr. Saxton wrote:

"Bombs can strike decks at or close to the normal. The normal being striking at a right angle. This is what makes bombs a more dangerous threat than long range shell fire."

This would certainly seem to represent at least a reasonably plausible hypothesis, but without more data, it's impossible to determine how generally accurate it might actually be. Validating this hypothesis, or at least setting some bounds on its likely utility, requires mathematical testing, which in turn requires some idea of exactly what is being compared. Do we compare bombs and shells of equal weight or equal caliber? What is the gun range, and what is the initial velocity of the firing gun? At what speed and altitude is the bomb released.

We can do some comparisons 'in our head'. Will a 2000 lb armor-piercing bomb dropped from 12000 feet penetrate more deck armor than a 12" projectile fired from a range of 6000 yards? Probably. Will a 1000 lb armor piercing bomb dropped from 1000 feet penetrate more armor than a 2700 lb bullet fired from a range of 35000 yards? Probably not. Everything, or at least almost everything, 'in the middle' remains somewhat up for grabs...

So enough specification to determine terminal conditions is essential. Once terminal conditions are specified, then assessing relative armor penetration via the application of some kinetic energy model is fairly straightforward, but until we know more about the weapons to be compared, we do not know enough to specify the terminal conditions in the first place.

So although I am glad to run individual cases, once specified, I'm hesitant to even begin to endorse any overall generalizations vs the armor penetration of bombs vs projectiles. I'm not sure that it can be done.

Bill Jurens.

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Re: British postwar tests on armor

Post by Herr Nilsson » Tue Apr 30, 2019 8:32 am

dunmunro wrote:
Mon Apr 29, 2019 3:51 am
This is from Whitley:
...The bomb struck and penetrated the upper deck forward of "A" turret and was deflected aft by the longitudinal armoured bulkhead at frame space 185,6, subsequently exploding on the armoured deck by a hatch and ventilation trunk, in the seaman petty officers' mess. The vertical bulkhead was ruptured and fire spread to the forward crew space through this hole, but the bomb did not penetrate the armoured deck. This was distorted by the force of the explosion. However, the hatch to the 28 cm magazine is believed to have been open (it could not subsequently be found) and the flash and splinters entered the magazine...
So we don't actually know that the magazine hatch was open but the whole sequence of events is strange. What is certain is that the 2in weather deck was cleanly penetrated.
According the German short report from February, 28th 1942 the armoured deck was knocked open and destroyed. There is no mention of any hatch.
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Marc

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Re: British postwar tests on armor

Post by paul.mercer » Tue Apr 30, 2019 9:35 am

To Dave, HMSCF and Bill,
Many thanks indeed for your replies, it would appear from the tests on the 'Nelsons' that even after all their experience of dropping bombs, the RAF still had a problem with accuracy. I seem to remember that when the tanker 'Torry Canyon' hit the rocks (in the 60's i think) they were trying to bomb her to set the oil alight, this was filmed by the BBC and showed an embarrassing amount of misses -and she was a very large ship stuck on the rocks!
Even a highly experienced squadron like 617 had problems hitting Tirpitz so it seems that the only practical way to hit a moving ship was by dive bombing but obviously not practical with a 6 ton bomb!!
Thanks again.

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Re: British postwar tests on armor

Post by dunmunro » Tue Apr 30, 2019 9:58 am

paul.mercer wrote:
Tue Apr 30, 2019 9:35 am
To Dave, HMSCF and Bill,
Many thanks indeed for your replies, it would appear from the tests on the 'Nelsons' that even after all their experience of dropping bombs, the RAF still had a problem with accuracy. I seem to remember that when the tanker 'Torry Canyon' hit the rocks (in the 60's i think) they were trying to bomb her to set the oil alight, this was filmed by the BBC and showed an embarrassing amount of misses -and she was a very large ship stuck on the rocks!
Even a highly experienced squadron like 617 had problems hitting Tirpitz so it seems that the only practical way to hit a moving ship was by dive bombing but obviously not practical with a 6 ton bomb!!
Thanks again.
Nelson was used a test target by FAA Barracudas, but their accuracy was poor because they had to release their 2000lb bombs at very high altitude to have any chance of penetrating the MAD.

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Re: British postwar tests on armor

Post by Dave Saxton » Tue Apr 30, 2019 1:39 pm

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: British postwar tests on armor

Post by Bill Jurens » Tue Apr 30, 2019 4:29 pm

Good posting.

I guess we (or perhaps only I) got mixed up in phrasing. It's a chain calculation and should work either way...

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Re: British postwar tests on armor

Post by dunmunro » Tue Apr 30, 2019 7:25 pm

Herr Nilsson wrote:
Tue Apr 30, 2019 8:32 am
dunmunro wrote:
Mon Apr 29, 2019 3:51 am
This is from Whitley:
...The bomb struck and penetrated the upper deck forward of "A" turret and was deflected aft by the longitudinal armoured bulkhead at frame space 185,6, subsequently exploding on the armoured deck by a hatch and ventilation trunk, in the seaman petty officers' mess. The vertical bulkhead was ruptured and fire spread to the forward crew space through this hole, but the bomb did not penetrate the armoured deck. This was distorted by the force of the explosion. However, the hatch to the 28 cm magazine is believed to have been open (it could not subsequently be found) and the flash and splinters entered the magazine...
So we don't actually know that the magazine hatch was open but the whole sequence of events is strange. What is certain is that the 2in weather deck was cleanly penetrated.
According the German short report from February, 28th 1942 the armoured deck was knocked open and destroyed. There is no mention of any hatch.
Thanks for that info. Could you provide more details?

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