The bomb that sank the Arizona

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paul.mercer
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The bomb that sank the Arizona

Post by paul.mercer » Mon May 11, 2020 9:34 am

Gentlemen,
I was watching a documentary on the exploration of the inside of USS Arizona by ROV the other day and it was stated that the ship was sunk by a 16" shell in an encased streamline casing dropped from around 10,000 feet that went clean through all the decks and exploded in a magazine, presumably the one that held the cordite charges. The Arizona was a WW! built ship of around 30,000 tons so presumably was not so heavily armoured as later ships (although it seems that the US navy managed to do what the RN could not and fit 12 x14" guns in a ship of less than 35000 tons!) I digress, given the expertise that has been expressed on the subject of shell v armour and plunging fire, in this Forum. i wonder if you might answer yet another of my questions.Would later ships like the KGV's Bismarck. Tirpitz the Iowa's and Yamato's have withstood the same bomb, bearing in mind it would presumably be falling vertically as opposed to normal battle fire?

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jabeque
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Re: The bomb that sank the Arizona

Post by jabeque » Mon May 11, 2020 11:56 am

Basically the context is very different from a projectile. The angle of incidence was almost 90º. Plunging-fire is about 30-45º in the most favourable case and with very low possibility of impact.

In the 20s, it was known that a piercing bomb, dropped high enough, would beat any possible armoured deck system. The problem was that the possibility of impact to a moving ship was very low. Therefore, the dive-bombing, was developed.

OpanaPointer
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Re: The bomb that sank the Arizona

Post by OpanaPointer » Mon May 11, 2020 12:01 pm

The shell was machined down to allow the fins to be fitted. Speculation is that this overheated the shells and degraded the hardening.

paul.mercer
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Re: The bomb that sank the Arizona

Post by paul.mercer » Tue May 12, 2020 9:05 am

gentlemen,
Thanks for your replies,
You state that this was known about in the 20's, but surely armour and armoured decking had improved considerably since then and the ships that I mentioned were all presumably built on the basis that they would not only have to fight others with similar or more powerful armament as well as having to contend with larger aircraft carrying heavier bombs? When Yamato and Musashi were sunk it was with a combination of bombs and torpedoes and I have always assumed (rightly or wrongly) that it was the torpedoes that did most of the damage. Did the US developed a purpose built armour piercing bomb that could penetrate their decks or did they follow the Japanese idea of modifying a 16" shell or are we to assume that no WW2 battleship was proofed against a heavy bomb falling almost vertically?
I have to say that looking at pictures of h two Japanese ships which appear to have so much anti aircraft armament that they resemble the spikes on hedgehogs, that the fact that this could not protect them meant that the day of the battleship was truly over.

paul.mercer
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Re: The bomb that sank the Arizona

Post by paul.mercer » Tue May 12, 2020 9:06 am

Gentlemen,
Sorry, double post again, must keep fingers off mouse!

Mostlyharmless
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Re: The bomb that sank the Arizona

Post by Mostlyharmless » Tue May 12, 2020 10:21 pm

There are a fair number of bomb hits on modern battleships in WW2 and we can make some guesses about what would happen.

For example, the IJN scored a single 500 kg bomb hit on Prince of Wales with a level bomber from about 2,500 metres, which was stopped by the 160 lb on 40 lb armour over the machinery although the explosion did cause PoW to sink faster. A bomb from 2,500 metres is moving at similar speed to a bomb dropped from a dive bomber at about 5,000 ft because the dive bomber is diving at about 300 knots. Thus this is comparable to the FAA hits on Tirpitz with 1,600 lb bombs of which all but one were stopped and the one that penetrated was too damaged to explode.

However, if the aircraft is higher when the bomb is dropped, penetration is increased. Thus three hits on Scharnhorst at La Pallice with 1,000 lb bombs from 14,000 ft all penetrated (rather too well as they went through the bottom). This inspired the H41 redesign and (according to that famous source Wikipedia) the deck was increased in thickness from 120 mm (4.7 in) to 200 mm (7.9 in) and the sloped armor at the edges was thickened from 150 mm (5.9 in) to 175 mm (6.9 in). Interestingly, there was a 1942 proposal to strengthen the main deck of Montana to 8 inches to help those ships resist bombs dropped from medium to high altitude.

The Littorio class suffered hits from British and American bombs in the 1000 lb or 2000 lb class, which all avoided the main deck. Two hits on the very strong turret roofs were defeated by the slopped 200 mm armour whilst the other hits caused flooding.

Finally, there were bigger bombs such as Fritz-X or even Tallboys, which were rather destructive.

paul.mercer
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Re: The bomb that sank the Arizona

Post by paul.mercer » Tue May 26, 2020 9:07 am

Gentlemen,
Thanks again for your replies.
just as an afterthought, as we know the RAF used 6 ton tallboys to sink Tirpitz. Thinking about the success the Japanese had t Pearl Harbour with their modified 16"shells dropped from around 10,000 feet and bearing in mind the huge carrying capacity of a Lancaster, would they have been better off adopting the Japanese shell modifications and carrying 6 or more heavy bombs which would have almost certainly given a larger percentage of hits or,
on the other hand, would they not be so effective as as Tirpitz was much more heavily armoured than Arizona?

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