HMS Hood's armour layout

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Dave Saxton
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HMS Hood's armour layout

Post by Dave Saxton » Sat Mar 13, 2010 3:24 pm

I have a cross sectional drawing of the Hood that shows its armour layout. I'm not sure about how accurate it is? The side armour is sloped 11* with three belts. The upper belt is shown as 127mm, the middle belt is shown as 178mm, and the main belt is shown as 305mm. The belt data seems to be correct, but the deck lay out is where I have questions.

The armoured decks (On the drawing) consist of an array of three thin decks outboard. On the drawing this array does not extend inboard to cover the ships centerline but is terminated by an inboard long. armoured bulkhead of 25mm. The protected three decks are labeled 51mm for the upper deck, 25-19mm for the battery deck, and 51mm for main deck, which has scarps (also 51mm), with the scarps sloped downward at about 53* behind the main belt.

One question I have is the materials and method of contruction of these protected decks. Are these laminates consisting of a structural componant and a plate, or are these single plates of Protective plating?
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Re: HMS Hood's armour layout

Post by marcelo_malara » Sat Mar 13, 2010 6:40 pm

Hi Dave. For what I can see in AOTS, double plating were applied directly over the beams on the forecastle deck and main deck, for 2" thickness, and single plating on the upper deck, for .75". Bear in mind that you are naming wrongly the decks. Hood had only two complete decks above the water line, with a single ´tween decks, and a forecastle above. Inside the 1" bulkhead, she had on the main deck 1.5" over the machinery and around the boiler uptakes, which were rather big. Hope this helps.


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Re: HMS Hood's armour layout

Post by Thorsten Wahl » Sat Mar 13, 2010 7:51 pm

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Re: HMS Hood's armour layout

Post by Dave Saxton » Sun Mar 14, 2010 2:32 am

Thank's guys. The cross sectional drawing in Bill's article is virtually identical to mine. It makes clear the upper deck and the main armoured deck are laminates as Marcelo describes. This was one thing that I needed to know.
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Re: HMS Hood's armour layout

Post by RobertsonN » Wed Jan 26, 2011 10:27 am

I too have a question about the Hood.

In 'The Grand Fleet' Brown states that the Hood's inclined 12 in belt was the equivalent of a 14 or 15 in vertical belt. This was the view also, I believe, of Attwood, one the the RN's constructors around 1920. Later, in the 1930s, the RN changed its view and official immunity zones show that the inclined belt was not considered better than a vertical one. At the second enquiry into the loss of the Hood, the ordnance expert Offord stated that the Hood's 12 in inclined belt (most sources give inclined at 12 deg but sometimes 10 deg) plus 1.5 in of backing plus 2 in sloping deck (two 1 in HT plates) was the equivalent of a 13 in vertical belt.

I realize the answer depends on what range (and therefore angle of fall) is desired for the inner edge of the immunity zone. As Hood was of pre-Jutland design where the outer edge (depending on ricochet from the decks and burster + splinter effect for hits on the side above the main belt) was only about 18000 yds, the inner edge would need to be about 10000 yds.

I'd be interested in your opinions on this one. Of course it also touches on the value of inclined belts in general.

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Re: HMS Hood's armour layout

Post by Tiornu » Wed Jan 26, 2011 8:56 pm

For the plate thickness of British warships, 1 inch = 24.9mm.
It is my understanding that, during this period, the British never used HT plates thicker than 1 inch. So if the deck is more than 1in thick, it has to be laminated. Even thinner decks may be laminates. The only reason I can guess for this is for increased structural strength--no joint runs through the whole deck.
I have never heard that the RN decided an inclined belt was no more shell-resistant than a vertical one. That would have been untrue. The decision to forgo inclined belts in their modern designs had to do with complication in construction and repair and the matter of shells slipping under the belt into the TDS.

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Re: HMS Hood's armour layout

Post by RobertsonN » Thu Jan 27, 2011 9:15 am

Yes, in Britain, I in always meant 40 lb plate (the real value of one square ft of 1 in thick plate was 40.8 lb I believe).

Before the Nelson, all RN ships had laminated decks of HT plate, with max. 1 in thick plates. The thicknesses for all apart from the protective deck were determined from structural strength considerations I believe, and on Hood because of the great length and turrets located far apart these thicknesses were generous. After Jutland, I in plate was added to magazine crowns of most ships. On the Hood, thickness was increased to 3 in places for protective purposes. HT plate was still used for reasons of economy.

I agree that the change back to vertical belts in the 1930s was made for the reasons you give.

If you look at http://www.admirals.org.uk/records/adm/adm/-9387.php for immunity zones of many capital ships in 1935 you will see that the 12 in sloped belt of the Hood was rated as a little inferior to the 13 in vertical belts of the Queen Elizabeth and R classes.

Official figures for 1939 are also given on that site: .../adm239/adm239-268.php

These show that the QZ and R classes were now rated as being safe down to 2000 yds lower than the Hood, which looks like they were now not seeing any advantage in the sloped belt. I agree with you that this view is simply wrong, but if anybody knows what quantitative advantage the inclined belt of the Hood gave it, I would be pleased to hear from them. Btw, that Royal Navy Flag Officers 1904 - 1945 site is a good one, with copies of some original documents.

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Re: HMS Hood's armour layout

Post by Tiornu » Thu Jan 27, 2011 4:33 pm

The RN used nickel steel for its deck protection until starting to switch over to HT in the Orion class (and perhaps Lion?).
I was going to guess that Hood's reduced immunity had to do with armor quality, but then you mentioned the old battleships. My second thought was that Hood's main belt height was skimpier, but QE's was about as skimpy as it gets (I have more height than QE's main belt thickness). Final guess is that the calculations looked at more than just the belt itself: Hood and "R" had an unfortunately exposed deck, perhaps aggravated in Hood by the belt incline.
There's no simple equivalence of inclined to vertical belt except at a specified angle. Vertical belts benefit more as the target angle swings away from the perpendicular.

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Re: HMS Hood's armour layout

Post by tommy303 » Thu Jan 27, 2011 6:08 pm

It is possible too, that the downgrading of Hood's belt resistance came as a result of newer AP shells and caps coming into service in the RN during the late 1920s and 1930s. Improved shell designs were better able to cope with inclined armour and to counter the improvement, designers who stuck with inclined belts tended to increase the angle another 3 or 4 degrees over the 12 degrees Hood's belt had.

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Re: HMS Hood's armour layout

Post by RobertsonN » Fri Jan 28, 2011 9:07 am

Thanks. Perhaps new shells and different assumed target angles both played a part.
The new, more aerodynamic 15 in shells, had flatter trajectories, greater vertical penetration (14 in at 15000 yards rather than 12000 yds) but poorer horizontal penetration.
In the First War, at Dogger Bank and Jutland, the British battlecruisers were nearly always well aft or well forward of their oppenents. Perhaps by the 1930s it was expected the Hood would need to function as a fast battleship and sometimes be abeam of the enemy.
In the detailed analysis of the loss of the Hood by Jurens, the ballistics expert Nathan Okun calculated how changing target angle altered the value of the Hood's protective layout. Assuming a range of 18100 m with an angle of fall of 14 deg and the Bismarck 37 deg forward of the beam (total obliquity 44 deg), the German 15 in shells could penetrate 240 mm of armor inclined as in the Hood. The 7 in armor would bend shells towards the normal so that the shell ended up going 2 deg upwards. This meant the shell passed over the main protective deck, and especially the vulnerable sloping part of it. Even the 5 in armor would deflect a 15 shell so that its angle of fall was now only 6 deg, which would likely have resulted in a ricochet on the upper deck. However, the final 20 turn would have put the Bismarck only 17 deg forward of the beam (total obliquity 28 deg). Now the German 15 in could penetrate the Hood's main 12 in belt. The 7 in armor would now produce little deflection. A shell would still have an angle of fall of 13 deg after penetrating the 7 in belt, and one striking the lower part of this would be able to strike the vulnerable slope of the protective deck. I believe that the expedition to the wreck of the Hood found that it was about half way through the 20 deg turn.
Other navies also used different target angles for different classes of ship. The US navy calculated immunity zones for battleships for a 90 deg target angle but used a 60 deg target angle for cruisers.

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Re: HMS Hood's armour layout

Post by RobertsonN » Mon Jan 31, 2011 3:38 pm

A further consideration points in the direction of Hood's belt armor being intended for oblique impact. Its barbette armor was of uniform thickness at a given level (12 in above the upper deck), whereas all British battleships had graded barbette armor (the QE and R classes, 10 in on the beam and 7/8/9 in on the centreline according to position). This choice seems to indicate the intended deployments of particular classes of ship.

Applying this idea to WWII ships, American, British and Japanese battleships had graded barbette armor because use in the line of battle was a distinct possibility for these navies that had considerable numbers of battleships. On the other hand, French, German and Italian battleships had uniform barbette armor at a given level. Evidently, these navies, with very small numbers of battleships, considered that chase or retreat scenarios were much more probable for their ships. The question of barbette armor has come up on this site (Bismarck/Sodak comparison) but the question of grading was not, I think, mentioned. The fact that ships of different navies were optimized with different scenarios in mind does complicate battleship A versus battleship B comparisons.

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Re: HMS Hood's armour layout

Post by Tiornu » Mon Jan 31, 2011 4:19 pm

I don't know that there's anything instructive in that. If a plate CANNOT be hit at a direct angle by any opponent on any bearing, then you may choose to thin that plate. It doesn't imply a preference for a particular target angle.

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Re: HMS Hood's armour layout

Post by RobertsonN » Mon Jan 31, 2011 4:52 pm

There is always a section of the barbette at about 90 deg to an opposing ship irrespective of its bearing. That is why ships intended for the battlecruiser role could not thin armor on the centreline (apart from maybe where shielded by another barbette). Ships of the line were intended to deploy 'just in time' at about 90 deg to the enemy, in which case the centreline of the barbettes could safely be reduced.

One sees this also in US ships. Battleships were designed for 90 deg target angle and had very heavily graded barbettes in later ships. Cruisers were designed for 60 deg target angle and had uniform barbette thicknesses.

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Re: HMS Hood's armour layout

Post by Bgile » Mon Jan 31, 2011 10:28 pm

I was under the impression that barbettes were given graduated armor in battleships because they were shielded by other barbettes or an armored conning tower. It's not a good idea to waste the weight if it isn't ever going to receive a direct hit.

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Re: HMS Hood's armour layout

Post by Tiornu » Tue Feb 01, 2011 12:42 am

Didn't Alaska also have gradations in her barbette armor?
I think this must be a feature restricted to new ships, at least as far as the Americans are concerned. I'm looking at Nevada, and her barbettes have the same thickness all around.

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