Comparing Montana's bomb deck armor to Yamato's Question?

[petsan]

Comparing Montana's deck armor to Yamato's I have found a problem.....over and over I have read that it was better to concentrate deck armor against bombs

Question #1....Montana's 2¼" laminated weather (Bomb) deck was the ¾” thick STS the structural substrate, leaving the 1½” thick STS plates as deck armor used for protection or was the 1½” thick STS the structural substrate leaving the ¾” thick STS plates as deck armor used for protection?

Question #2....The Yamato used lighter "D" type armor for her two upper decks leaving the 7.8" to 9” Armor hard armor for her Armor deck, the Montana
used a thicker and heavier type 2¼" STS armor for her upper decks leaving a slightly thinner 7.05" to 7.35" Class B for her Armor deck.......Which was better
from an Aerial warfare perspective IE, if germany attacked your battleship at Malta with 550 and 1,100lb HE/SAP type bombs (carrier HMS Illustrious) which of the two would fare better (just hits...not talking about air defence guns)?

The "Never-built" Montana had a 2¼" weather (Bomb) deck of made up of two laminated plates
a (19mm) ¾” thick STS and (38mm) 1½” thick STS plates
The main armor deck Amidships-centerline was 7.05" Class B (147mm + 32mm) 5.8" on
1¼" STS structural substrate and Amidships-outboard was 7.35" Class B (155mm + 32mm)
6.1" on 1¼" STS structural substrate, and a third deck of 0.625" centerline (16mm) ¾” outboard (19mm)
......A total of 10.35" of steel at its maximum.

Yamato had
D steel 1/2"- outer 1.42" Weather (Bomb) deck (.79 OVER .63= 1"+ sts EQUIV)
.39" - outer 1" second deck (1" D STEEL = less than 1" sts EQUIV)
7.8" to 9” Armor third deck
1/4" Splinter deck over
.375 fourth deck

[USSWisconsin]

The bomb deck was supposed to initiate the bomb's fuse - causing the bomb to detonate before it contacted the armored deck. In general one plate of a given thickness is more resistant than two laminated plates adding up to that same thickness. This was explained as a flexing issue, the laminated plates could flex/yeild separately, while the single plate would have to flex alone. This flexing led to failure, so if the thick single plate did not yeild at all - it would work as designed and protect the ship without being damaged. Explosives attack armor much like the HESH warhead, casuing spalling on the rear of the plate or vaporizing the plate if used in sufficent quantitiy. Having the bomb detonate further away from the armored deck is desirable.

In the case of the multiplate designs, these were not used because they were superior in protection qualities to a single plate, but because they could be built more easily, while using a single thick plate was not one of the options available. To produce an armored deck like these as a single plate would be quite difficult - even today. By using multiple plates, the joints in each layer could be staggered, and the weldable STS could be tied into the ships hull girder, and the thick Krupp armor could be produced and handled in more manageable pieces.

IMO the 9" deck of the Yamato offered more protection than the 7" deck of the Montana. Neither of those decks was ever penetrated by a bomb - so there is no experimental evidence proving my analysis. The Yamoto's armor was tested and a turret faceplate and other samples proved to be of good quality. While US armor was superior, I don't have reason to beleive a 7" American armor plate was superior to a 9" Japanese armor plate (the 7.8" IJN might be close to equivalent to the 7" US). I don't beleive 1100# SAP bombs could penetrate either ships armored deck from operational altitudes where a hit would be likely in WWII. The Yamoto's deck needed a substrate too - it wasn't made of butt welded plates - the blueprints have not survived - but the Anatomy Of The Ship book about her may have details.

[Dreadnought]

Have to disagree here about bomb penetration aboard the Yamoto. Although Yamato is claimed to never have her deck armor peirced, her sister Musashi did have its deck armor and armor deck peirced by a US dropped bomb. Just after 12:03 on October 24th 1944 Musashi was attacked by US bombers. This pentrating hit struck just forward of #4 AA mount. It penetrated the upper deck and the main deck and exploded on the mid deck. This explosion killed all crew in the munitions chambers below. This explosion also caused #2 engine room (port inboard) to fill up with steam making it unmanable which in turn took out shaft#2. Leaving Musashi with only three propellers operational.

Although hit in the upper works by several bombs which wrecked it pretty good including the bridge, and among several torpedo hits, this bomb was one of two bomb hits that Captain Iguchi reported to Kurita aboard the Yamato as doing considerble damage.

So IMO, There is no doubt that the vitals of these sister ships although heavily armored was out of reach of US aerial bombing via direct hits on the decks. The fact that the Japanese BB's were designed differently then their american counteparts is of no consequece. It did however prove one theory though that one need not inflict direct damage on a compartments armored exterior when one can jar or damage the machinery located in that compartment and render the compartment useless. Or hit a compartment above and that damage aid in disabling the compartment below. In this case, #2 engine room. If we think about it, even a direct bomb hit in the area of the funnel could in theory do the very same thing by damaging the exaust stacks. The ship could still sail but those gasses would get released internally and be a major factor in hampering the crews ability to sail.

This information (outside of my own speculations) came from Battleship Musashi by Akira Yoshimura. Japans leading non-fictional author on military and naval subjects.

[petsan]

Thanks Dred just bought Battleship Musashi by Akira Yoshimura on amazon....$3. used
didnt have that one
At first I agreed with Wisco on the single thickness armor but reading about aerial bombs and what
they did in WW2 I kind of agree with Dred that it was better (ala Montana) to keep those bombs as far
away from the Armor deck and to keep them out entirely if at all possible......The design team on Montana
had previously only put 1.5" STS in the bomb (Weather) decks of the Iowas and their predecessors, and I have also
just read that they were thinking (just before Montanas cancellation) to thin the 16" belt to 12" and increase
Montanas bomb (Weather) deck to a whopping 3" of STS.......so I guess they also concurred with Dred

What Im still confused about was Question #1....Montana's 2¼" laminated weather (Bomb) deck was the ¾” thick STS the structural substrate, leaving the 1½” thick STS plates as deck armor used for protection or was the 1½” thick STS the structural substrate leaving the ¾” thick STS plates as deck armor used for protection?

Anybody know which thickness was substrate and which was aarmor, Ive searched to the ends of google and no luck...

[USSWisconsin]

By Multiplate, I meant on one deck. Having a thicker bomb deck is definantly good, more bombs will be excluded, and the largest ones would be slowed down more and still detonate further from the armor deck. So I was comparing just the 7" vs 9" armor on the armor deck. Overall the Montana was better protected than the Yamato, there were known flaws in attachment points for the Yamato's and they failed during the sinkings, I don't know if the 9" plate was penetrated of if the backing colapsed from the deck hit, given the attachment issues with armor. It might wave come in through a damaged area - or found a designed deck penetration. I wonder about that bomb? Was it a special bomb? Perhaps a 4000# bomb? 9" of good deck armor should keep out a 1000# bomb.

[Dreadnought]

*Found another glitch in the "matrix". My post contains 2 "Yamato's" in a row but when opened for editing there is an "although" that does not appear in the post at all in front of the second "Yamato".

[Dreadnought]

By Multiplate, I meant on one deck. Having a thicker bomb deck is definantly good, more bombs will be excluded, and the largest ones would be slowed down more and still detonate further from the armor deck. So I was comparing just the 7" vs 9" armor on the armor deck. Overall the Montana was better protected than the Yamato, there were known flaws in attachment points for the Yamato's and they failed during the sinkings, I don't know if the 9" plate was penetrated of if the backing colapsed from the deck hit, given the attachment issues with armor. It might wave come in through a damaged area - or found a designed deck penetration. I wonder about that bomb? Was it a special bomb? Perhaps a 4000# bomb? 9" of good deck armor should keep out a 1000# bomb.

From what the book reads they were GP bombs "general purpose" some are noted as being 250kg but the ones that did this damage are not noted for their weight.

[petsan]

An SB2C-3 Helldiver tagged Musashi with one or two, It or they did not apparently penetrate, but through spalling disabled an engine room. The bombs used were probably the AN-Mk33 1,000 lb armor piercing bombs, of which two could be carried by the SB2C. This weapon was a common available load out in USN CVs during WW2, although not the primary load out....a late war Essex class carrier might have between 10-20 such bombs. The AN-Mk33 weighed 1,008 lbs and had a 140lb Explosive D burster was 6 feet long and a foot in diameter and made of cast steel. Most likely hits on Musashi/Yamato were AN-Mk33s, because if not it means that Yamato's legendary armor was compromised by mere 1000lb SAP/GP bombs.

Another was the AN-M59 "semi" armor piercing 1,000lb SAP bomb, the standard USN anti-ship bomb, good for everything from a transport through a Cruisers.
The AN-M59 weighed 990 lbs and had a 315lb Amatol burster was 5.8 feet long and a 15 inches in diameter and made of cast steel.
Another was the AN-M58 "semi" armor piercing 500lb SAP bomb, The AN-M58 weighed 536 lbs and had a 143lb Picratol burster was 4.7 feet long and almost foot in diameter and made of cast steel.

[USSWisconsin]

On the Montana design, the bomb deck had a 60# STS outer layer and a 30# STS substrate. This makes sense, I have never seen thinner armor attached to the surface of thicker armor in the US battleships. I found the answer in Friedmans US battleships- and it isn't teribly explicit. This allows larger plates to be used as the backing, and smaller heavier plates to be attached to the face.

[petsan]

On the Montana design, the bomb deck had a 60# STS outer layer and a 30# STS substrate. This makes sense, I have never seen thinner armor attached to the surface of thicker armor in the US battleships. I found the answer in Friedmans US battleships- and it isn't teribly explicit. This allows larger plates to be used as the backing, and smaller heavier plates to be attached to the face.

Thanks Wisco, how did I miss that....I have that book, if you dont mind what page was that on and again thanks : )

[USSWisconsin]

Thanks Wisco, how did I miss that....I have that book, if you dont mind what page was that on and again thanks : )

pg 337, note; his reference to 60# side plating with ballistic eqivalence to bomb deck -plus order he listed the bomb deck plates - as I said not terribly explicit, but additionally - it would make no sense to put a thin plate on a thick backing in this case.

[Dreadnought]

In stark comparrison though the Iowas turret faceplates are in reverse. A thick armor plate of 17" backed by a thinner armor plate of 2.5".

[USSWisconsin]

In stark comparrison though the Iowas turret faceplates are in reverse. A thick armor plate of 17" backed by a thinner armor plate of 2.5".

That's what I said - the thick plate is on the outside - toward the enemy

Pg 254 in Seigfreid/Breyer shows the outer plate as 55#

The thinner plate tends to be available in bigger pieces, making it easier to arrange the seams so they don't line up with the armor plates attached to them - the thick plates are made in smaller pieces- since they are so heavy and are harder to handle. This makes it practical to use thin plate as the substrate and put the toughest plates where they will be hit first. I am taking about laminated plates, made up of two thicknesses of armor touching each other - not two separate plates where there is a decapping plate and a space behind it.

[Dreadnought]

That's what I said - the thick plate is on the outside - toward the enemy

Pg 254 in Seigfreid/Breyer shows the outer plate as 55#

The thinner plate tends to be available in bigger pieces, making it easier to arrange the seams so they don't line up with the armor plates attached to them - the thick plates are made in smaller pieces- since they are so heavy and are harder to handle. This makes it practical to use thin plate as the substrate and put the toughest plates where they will be hit first. I am taking about laminated plates, made up of two thicknesses of armor touching each other - not two separate plates where there is a decapping plate and a space behind it.

My bad, misunderstood. Read it as the other way around.

[zraver]

The bomb deck was supposed to initiate the bomb's fuse - causing the bomb to detonate before it contacted the armored deck. In general one plate of a given thickness is more resistant than two laminated plates adding up to that same thickness. This was explained as a flexing issue, the laminated plates could flex/yeild separately, while the single plate would have to flex alone. This flexing led to failure, so if the thick single plate did not yeild at all - it would work as designed and protect the ship without being damaged. Explosives attack armor much like the HESH warhead, casuing spalling on the rear of the plate or vaporizing the plate if used in sufficent quantitiy. Having the bomb detonate further away from the armored deck is desirable.

Not BB expert but I'll have to dissagree here. Laminated armors are generally stronger than single piece plates. Assuming a brickwall type pattern where there are no through and through seams the laminated armor has flex that does not require failure. Single piece armor pushed past its limits busts and results in a total failure. With laminated armor you need a double failure plus the natural flex inherent in laminated designs acts as a shock absorber stealing some of the impact energy needed to create those failures. Laminated armors also resist spalling better- much better becuase no matter how tightly bound there is a void the shack wave has to jump.