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The Chieftain Does History!


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#41 Adam_S

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Posted 23 December 2017 - 1512 PM

What about that 40mm plate inboard of the belt? Wouldn't that have some sort of role in stopping an 8" shell if it made it through the main belt? 100mm + 40mm on a bit of a slope doesn't compare too badly with a Des Moines, which Wikipedia lists as having a 4-6" (102-150mm) belt.


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#42 Ken Estes

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Posted 23 December 2017 - 1914 PM

...and if the 8-inch SAPC shell detonates at that point?

 

I am sorry, but if you think the armor system of the Spee in 1934 compares to the Des Moines class in 1946, I don't think you have been following. Those interior bulkheads are more about containing torpedo damage than limiting penetration effects of AP projectiles, which have already accomplished their principal mission at that point, i.e. opening up the target hull.


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#43 Adam_S

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Posted 23 December 2017 - 1920 PM

...and if the 8-inch SAPC shell detonates at that point?

 

...then you've kept it out of the magazines or engineering spaces if nothing else.


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#44 DB

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Posted 28 December 2017 - 2014 PM

Does the 40mm protect you from the burst fragments?


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#45 Markus Becker

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Posted 29 December 2017 - 1117 AM

40mm is 1.57". Standard type BB had a second armored deck of 1.5" to protect magazines and machinery spaces from splinters. But I have no idea how much room was between the two and there has to be some depending on the velocity of the shell and the response time of the fuse. 


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#46 Ken Estes

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Posted 13 February 2018 - 1949 PM

I have looked up the relevant chapter in my Friedman.

 

The New Orleans class were second generation CA. They displaced 1,000tons more than the first generation and were better protected but still not well protected. Theoretically magazines and machinery spaces were immune to 8” shell between 12(15) and 24k yards, provided the target angle of was 60 degrees or smaller. In reality that meant they were armored against destroyer gunfire. Which was important and something the first generation ships weren't. 

 

A guy who has probably forgotten more about US warships than I know once said that the first US CA that was protected from 8” standard shells in the sense protection is understood when it comes to battleships was the USS Salem. 

Finally i have my copy of Norman Friedman' US Cruisers in hand.

 

I think you would have been better off surveying the entire Chapter 5 on 'Second Generation Treaty Cruisers,' because it reveals what C&R (Bureau of Construction and Repair) considered as protection against 8-inch gunfire. Friedman's discussion of the 1927 discussion of improvements over the tinclads [Northampton class] speaks in terms of 7-inch belt and 2-inch deck armor (US Cruisers pp.139-41). noteworthy is this: "There was no hope, at this point, of protecting very much of a ship against the power of 8-in-gun fire; C&R would have to keep to the essentials [i.e. limited protection vs X-inch] (p.139)."  This is such a truism and why I alerted right away to any assertion that the Deutschland class might have been protected vs. 8-inch gunfire. To continue, a discussion of turret armor by C&R showed that a turret armor face of 5-in and armor roof of 3-in thicknesses would protect against 8-in. horizontal fire from 13,000 yards out, and plunging fire out to about 25,000 yards (pp. 142-43). The final design study for the New Orleans class showed that turrets with 6-in face plates sloped at 45 degrees, 2.25 in roofs "implied immunity against 8-in-gun fire beyond about 10,000 yards (pp. 144-45)."  "Further improvements were made in the course of detail design, so that the ships were completed with 5-inch barbettes.... The turrets had 8-in face plates, 2.75 in roofs, 3.75 to 1.5-in, sides, and a 1.5-in rear plate (p. 145)."

 

As for belt armor, "... the bureau increased side protection of the magazines from 4.25 to 5.75-inches, to achieve immunity against 8-in-gun fire at 60-degree target angle at 12,000 yards (p.150)." The 85-pound [2.25 in] deck armor over the magazine would be immune to plunging fire out to 22,000 yards.  "Machinery spaces were not nearly so well protected; they were covered by only a 40 lb deck [1.25 in] and side plate equivalent to about 2.6 inches. This belt armor was effective against 5-in-gun fire at a 60-degree target angle from 7000 yards out and against 6-in-gun fire at a similar target angle from 15,000 yards out. (p.150)"

 

The bureau spent remaining tonnage allowance to improve the New Orleans class deck protection over machinery spaces.  "The existing 40 lb deck could be penetrated by 8-in shell at 14,500 yards, by 6-in shell at 15,500 yards, and even by 5-in shell at 16,000 yards. The danger of loss of air pressure in the firerooms by a major rupture of the deck had to be considered. At a cost of about 350 tons, 60 lb plating could be quilted over the existing deck and immunity from 8-in fire achieved out to a useful 22,000 yards to match magazine protection (p.155)"  The increased armor of this class reduced the fuel capacity from 874,787 gallons (Portland class) to 614,626 gallons, a clear reversal of cruiser design doctrine. (p. 157)

 

So, now you can see why I was curious as to how the Deutschland class could have been considered as immune to 8-in gunfire. It's really far too tough a measure for any ship designed in the prewar period.


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