Yamato and Musashi vs. Missouri and Iowa

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Mostlyharmless » Sat May 03, 2014 11:45 am

It would be very surprising if a 1,000 lb bomb dropped by a dive bomber could penetrate a 190 mm armoured deck. Only one of the 1,600 lb bombs hitting Tirpitz got though the 80 mm deck and there are no other examples of dive bombers penetrating a main armoured deck of anything newer than Marat. However, it is quite possible that a bomb exploding in contact with the deck acted like a HESH shell and the shock wave sent spall downwards into the engine room (might the same thing have happened to Scharnhorst at North Cape?). I suspect that is why there is a 16 mm (5/8 inch?) STS plate about a foot below the main armoured deck of the South Dakota and Iowa designs.

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Steve Crandell » Sat May 03, 2014 1:57 pm

I have always assumed the damage was all above the MAD. There is quite a bit of important stuff above the MAD on any warship. Do we know it was actually penetrated by bombs?

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by alecsandros » Sat May 03, 2014 5:52 pm

Steve Crandell wrote:I have always assumed the damage was all above the MAD. There is quite a bit of important stuff above the MAD on any warship. Do we know it was actually penetrated by bombs?
... I have not found any clear reference. The best I have comes from Garzke and Dulin "Axis Battleships", as follows:
Attachments
Musashi sketch of hits.PNG
And this is the sketch of the damage suffered, where it appears the MAD was not perforated... but who knows ?
Musashi sketch of hits.PNG (162.65 KiB) Viewed 2509 times
Musashi bomb damage to port inboard engine room.PNG
This is the description of the damage caused by the second AP bomb.
Musashi bomb damage to port inboard engine room.PNG (148.83 KiB) Viewed 2509 times

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Steve Crandell » Sat May 03, 2014 7:39 pm

Odd. It appears that the bomb exploded over the MAD, but caused damage below it.

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Dave Saxton » Mon May 05, 2014 12:19 am

Japanese accounts indicate that it defeated the MAD. Homogenous armour doesn't eject spalls and splinters. There is either penetration or no penetration. Splinter damage to the turbine, confirmed by Japanese accounts, must come from the bomb (or a another munition). Three decks includes the MAD. (which according to Yoshimura's drawings was 200mm MNC over 10mm Ducol.)

However, the Japanese accounts mentioned that it set off munitions for the number 4 secondary mount in a munitions handling room below the MAD. The entire crew, including the the munitions handlers, for gun mount Number 4 were killed and the munitions chamber burned out. Did flash penetrate the munition chamber and secondary explosions send splinters spraying below the MAD?

Nonetheless, we need not assume that 200mm homogenous armour could not be defeated by a dive bomber released bomb in this case. It could. Such bombs can strike at the normal, and they can obtain sufficient velocity when striking at or near the normal to obtain full penetration. Striking at the normal, 200mm is not really that thick even for smaller AP.
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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Mostlyharmless » Mon May 05, 2014 3:14 pm

There was a post by Delcyros at NavWeaps Discussion Boards http://warships1discussionboards.yuku.c ... ine?page=4 which said:

Fritz X (=PC 1400 warhead) had sufficient penetration at low obliquity to just penetrate ROMA´s decks amidships the way it hit. It was rated and proof tested with a penetration of 130mm Wh/n.A.* single plate at 50 deg obliquity (german definition, implies 40 deg from the normal) with striking velocity of 270m/s. Penetration at 60 deg (=30 deg to the plates normal) is given with 160mm Wh/n.A.

As a dive bomber is unlikely to be descending faster than 200 m/s (Mach 0.6), I don't see how the bomb could be moving at 270 m/s unless it is dropped from 1,677 metres, which is high for a dive bomber. It was also only a third of the mass of a Fritz X. Thus, if what Delcyros said was true, then hiding under a single 160 mm plate looks as if it should have been safe.

According to “U.S. Battleships: An Illustrated Design History” by Norman Friedman, the designers of South Dakota seem to have felt that it was necessary to place splinter armour behind (or below) homogeneous armour. For example on page 283 “Then, since it was now expected that shells might actually strike the lower portion of the belt, splinter protection had to be provided inboard of it” or “However, the boilers (see below) penetrated the third (splinter) deck and had to be covered by a secondary splinter deck only 30 inches below the main armor deck,..”

Those ideas seem to relate to the impact of shells. HESH shells will cause spalling from homogeneous armour but I don't have any idea what the explosion of a bomb with perhaps 315 lb of explosive (assuming that it was a AN-M59 1,000lb SAP bomb) would do as the bomb would presumably only be in contact along a ridge or a point rather than with the explosive stuck to the surface.

I like the idea of flash penetrating to a handling room and that seems a very plausible interpretation of what happened.

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Dave Saxton » Mon May 05, 2014 6:55 pm

The danger of the dive bomber released bomb is that they strike at or very near the normal, not 40 or 30 degrees from the normal. I don't see how an AP bomb burst could create any kind of plasma jet effect on homogenous armour.
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Re: Yamato and Musashi vs. Missouri and Iowa

Post by tommy303 » Tue May 06, 2014 12:52 am

The bomb which created such havoc in the engineering spaces might have been an AP AN Mk 33. At 1000-lbs it was capable of being delivered by dive bombing. The filler was approximately 140-lbs of cast TNT or compressed Explosive D. The fuze was an AN MK228 with a .08 second delay. It is possible the bomb might have detonated in the armour and holded it causing bomb and armour fragments to be projected into spaces below the armoured deck.

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Dave Saxton » Tue May 06, 2014 3:16 pm

Yamato had a thin deck between the MAD and the engineering spaces according to drawings. If there were spalls it should have caught these. The possible need for a deck to catch spalls is reflective of the quality of the homogenous armour. Pieces should not break off of high quality homogenous armour. It should pedal if stretched that far instead. Plate debris does indeed become ejected in the case of face hardened armour. Otherwise a spall catching deck is a very inefficient use of armour weight. Why not just put that additional weight into the main homogenous plate where it can do some good?

By 1944 a 1,600lb American AP bomb for dive bombers was also available. I pretty sure the Helldiver could carry it. It was supplied to the British for use by the Barracuda. The CAG report for Enterprise's dive bombers mention the use of the 1,000lb bombs, but the hit in question was received prior to the Enterprise strike from a different CAG.
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Re: Yamato and Musashi vs. Missouri and Iowa

Post by alecsandros » Tue May 06, 2014 4:08 pm

Dave Saxton wrote:Yamato had a thin deck between the MAD and the engineering spaces according to drawings. If there were spalls it should have caught these. The possible need for a deck to catch spalls is reflective of the quality of the homogenous armour. Pieces should not break off of high quality homogenous armour. It should pedal if stretched that far instead. Plate debris does indeed become ejected in the case of face hardened armour. Otherwise a spall catching deck is a very inefficient use of armour weight. Why not just put that additional weight into the main homogenous plate where it can do some good?

By 1944 a 1,600lb American AP bomb for dive bombers was also available. I pretty sure the Helldiver could carry it. It was supplied to the British for use by the Barracuda. The CAG report for Enterprise's dive bombers mention the use of the 1,000lb bombs, but the hit in question was received prior to the Enterprise strike from a different CAG.
... We know there were limits to a cemented armor's maximum thickness before it started to lose resistive quality. Thus a US average post-1930 class A cast could go up to 12", or 305mm thickness before starting to lose effective resistance. 400mm class A would probably be more like 360mm class A in terms of overall quality and stoping power of BB caliber shells.

I would expect this phenomenon to appear in homogenous armor casts also, but at much thinner dimensions - probably from 150mm onwards...

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by tommy303 » Tue May 06, 2014 5:25 pm

By 1944 a 1,600lb American AP bomb for dive bombers was also available. I pretty sure the Helldiver could carry it. It was supplied to the British for use by the Barracuda. The CAG report for Enterprise's dive bombers mention the use of the 1,000lb bombs, but the hit in question was received prior to the Enterprise strike from a different CAG.
Hi Dave,

In that case, the 1600-lbs AP would have been the AP AN MK1, with a bursting charge of 215-lbs of cast TNT or compressed Explosive D. The fuze would have been the same as that used in the 1000-lbs AP bomb (AN MK228 with a .08 second delay).

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Dave Saxton » Wed May 07, 2014 1:50 pm

Hi Thomas,

I have the battle reports of Joe Lawler and Dan Smith, both from the Enterprise. Dan Smith was the CAG. Their reports state the use of the 1,000 lb AP. However as far as I can tell this was the third air strike against Musashi and the hit in question happened during the second air strike. The bombs used by the second strike may have also been 1,000 lbers but its possible they were 1,600 lbers.
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Re: Yamato and Musashi vs. Missouri and Iowa

Post by Dave Saxton » Wed May 07, 2014 2:14 pm

alecsandros wrote:
I would expect this phenomenon to appear in homogenous armor casts also, but at much thinner dimensions - probably from 150mm onwards...
Most homogenous armour is rolled not cast, but the Germans found that the plate thickness of homogenous armour should not exceed a maximum of about 15cm. Indeed, Krupp found that to retain the highest possible quality, the plate thickness should not exceed about 100mm. The US tried to use very thick homogenous plates of up to 17" as a substitute for their very poor quality Class A plates. However, this was not successful. The Naval Research LAB tried as late as 1945 to find ways of producing thick homogenous plates that retained the same standards of quality but it could not be done. The limit velocity of the thick homogenous plates was about 80% of what it should have been. 200mm plate thickness was probably not giving the full 200mm worth of protection.
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Re: Yamato and Musashi vs. Missouri and Iowa

Post by tommy303 » Wed May 07, 2014 6:56 pm

Armour, both cemented and non-cemented usually starts out as a cast ingot. Forming the plate or piece is then done by either hammering, forging (which allows the metal to be formed into various shapes and reduces the amount of work hardening associated with hammering), or rolling (which is usually less expensive and time consuming than the other processes). The armour then goes through final machining, cementing and decremental hardening in the case of face hardened armours; homgenous or non-cemented armours are merely tempered after final machining.

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Re: Yamato and Musashi vs. Missouri and Iowa

Post by tommy303 » Thu May 08, 2014 5:20 pm

It is possible to produce cast armour, and was done for armour in complex shapes which would be difficult to form otherwise--gun mantlets, tank turrets, etc., but large flat plates or lightly curved plates were normally forged or rolled.

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