Hoods armour

[paul.mercer]

Gentlemen,
I'm sure this topic has been discussed before somewhere, but I could not find it, so appologies for reopening it.
My question is this,Hood was apparently due to go in for a refit shortly before hostilities broke out and this was cancelled. I believe that the refit was to include the fiiting of extra armour, if this had been fitted do you think the outcome at Denmark Strait would have been any different - or would it still have been an old battlecruiser against a modern battleship with the same result?

[Thorsten Wahl]

distance at the moment of detionation was approximately 15000 m
projectile speed 569 m/s AOF 10,5 degrees

Hoods main belt was susceptible for perforations and detonation inside of the ship at compound obliquities(AOF/inclination of plate/target angle) up to ~36 degrees, considering a plate quality similar to modern german armor. I dont know if the "older" armor was comparable to newer qualities.
If the general quality was somwhat lower, than the possible compound obliquity for perforations increases somewhat,

At this distance any hit on the belt can be expected in a detonation well inside of the ship and possibly reaches vital parts of the ship
approximately one fourth of protected shiplenght were magazines/turrets and 3 fourth wer machinery spaces
According to the distribution of vulnerable areas you can also expect the hit distribution against the side protection

at 15 km you can expect hitprobabilities above 25% if MPI is on target (exact values ​​are not at hand)
(approx 1 hit per 4 gun salvo)

[Dave Saxton]

If it was anything like the Renown armour upgrade it would not be that significant of IZ extension. On Renown it was hodge podge of new plates layed over the old structure. There was a practical limit to how much to de-construct the ship in order to reconstruct the ship properly. At some point its just better to build a new ship on a new design.

[Neil Robertson]

Interesting question. I am looking at Hood: Design and Constuction by Maurice Northcott (1975).This contains armor layouts for both the alternatives considered, However, for a penetration through the main belt they are the same. While the main belt and the knuckle of the protective deck were unaltered, the deck below that formed the magazine crown became 2 in thick over its entire breadth. Earlier, as with other ships post-Jutland, the magazine crowns had 2 in HT directly above them but this protection was not extended outboard, leaving a considerable area of vulnerability. Whether this 2 in deck was HT or would have been 1.5 in NC + 0.5 in D is not recorded. Probably the former. If the 15 in shell exploded above this deck then it might have prevented the magazine explosion. However, as the shell probably penetrated the bottom of the 7 in belt and travelled through the rear engine room bulkhead before detonating in one of a number of 4 in magazines, this additional protection may not have mattered.

The German battle handling instructions for Bismarck against the Royal Sovereign put the latter's belt + protective deck as safe down to 6500 m for the Bismarck being 40 deg fore or aft of the beam (below that any penetrating shell would be broken up). From the battle handling instructions for Scharnhorst against the Hood and the Royal Sovereign, the former's side protection was a little better abeam and a little worse at 20 deg with both no complete penetration at 40 deg. So the belt + knuckle of Hood should have been adequate down to 7500 m at 40 deg. The Germans thought the Royal Sovereigns decks were OK up to 20000 m. The Hood had in general better horizontal protection than RS. There remains the side above the main belt trajectory. Nathan Okun in his detailed analysis of the battle calculated that at 37 deg the 7 in belt would have deflected a 15 in shell at 2 deg upward from the horizontal, i.e. away from the magazines, and that a shell passing through the 5 in belt would be travelling downwards at only 6 deg from the horizontal. It would be also decapped and at such a shallow angle would richochet on the protective deck.

So my view is that strick maintenance of an inclination of 35 deg upwards would have been necessary for reasonable safety. Not to mention having the POW in the lead. Committing a 20+ year old ship was desperate but Britain was desparate that the transAtlantic convoy sytem was not suspended.

At the enquiry, Offord's opinion was that the belt + knuckle was secure against a 1600 lb 15 in shell with a muzzle velocity of 2690 fps (data from a Russian source) at 40 deg. Specically, that such a shell could penetrate a 10.5 in belt at that inclination. The RN officers seemed not to realise the increased penetrating power of 15 in guns and thus the necessity of maintaining a healthy inclination. However, in a 1942 report comparing KGV with Tirpitz, while confident about the former having the better protection, there a perhaps revealing phrase about maintaining an inclination of at least 30 deg, to 'guard against (possible) superpenetration, of the German shells'. Perhaps that is as near they got to admitting that it may have been bad judgement as well as bad luck that day off Greenland.

[Dave Saxton]

Nathan Okun in his detailed analysis of the battle calculated that at 37 deg the 7 in belt would have deflected a 15 in shell at 2 deg upward from the horizontal, i.e. away from the magazines, and that a shell passing through the 5 in belt would be travelling downwards at only 6 deg

Hmm... those values of trajectory change in these cases seem quite a bit off base to me.

The RN officers seemed not to realise the increased penetrating power of 15 in guns and thus the necessity of maintaining a healthy inclination

Exactly. As in:

Hoods main belt was susceptible for perforations and detonation inside of the ship at compound obliquities(AOF/inclination of plate/target angle) up to ~36 degrees

[alecsandros]

According to Nathan's study, British 1920s cemented armor had 85% - 90% of the resistance to perforation of British post 1930 cemented armor, at best...

[RF]

......would have been necessary for reasonable safety. Not to mention having the POW in the lead. Committing a 20+ year old ship was desperate but Britain was desparate that the transAtlantic convoy sytem was not suspended.

Well, it could have been worse. What if there was no POW to accompany Hood..... but Renown or Repulse instead? KGV had to cover the Faroes Shetland gap and could have been doing that practically on its own.

Had Bismarck been available two months earlier in March 1941 that would have been the scenario.

To me the real tragedy isn't Hoods armour or the lack of the refit that never happened because the Treasury wouldn't spend the money, but the fact that Hood opened fire on the wrong ship. We shall never know what would have happened if Hood had opened fire on Bismarck and hit Bismarck first..... after all Hood had the advantage of opening fire some time ahead of Bismarck.

[paulcadogan]

Paul

Gentlemen,
I'm sure this topic has been discussed before somewhere, but I could not find it, so appologies for reopening it.

Paul,

Don't know how you missed this - just a scroll down the current page in this subforum:

viewtopic.php?f=14&t=3877

Paul

[Thorsten Wahl]

According to Nathan's study, British 1920s cemented armor had 85% - 90% of the resistance to perforation of British post 1930 cemented armor, at best...

If this mean the ballistic limit was approximately 10% lower compared to german KCnA, Hoods facehardened armor had about 275mm effective thickness.
on the basis of the gKdos 100 pentrationcharts, the compound angle for succesful perforations became ~40 degrees.

still some toughts on angular performance of a given projectiles. british post war ballistic experiments on the angular performance of high quality projectiles and plates showing differencies for the nominally equal projectiles.

For given speed, where shooting documents predicts perforation at 60 degrees, the interval in wich the first projectile penetrates at given velocity and the angle where approximately 100% of incomming projectiles pentrates, was approximately 10 degrees wide. So ther is always some degree of uncertainty.
Nevertheless the penetrtion documents gave good clue for the projectiles, but one must also consider the limits of these documents.

The german Gkdos 100 documents for the naval guns for instance tend to give to low pentrations as the impact velocity rises above 600 m/s
This is due to the high exponent of 1.6 used in the general formula. Because it is a monomial formula, it can hardly handle the varius failure modes/failure combinations of plate and projectile (What about rebound, shatter, and so on). Nevertheless it gave good clue for the performance of german projectiles according to statements of leading german ballisticians of the time.

For comparison the british post WW2 ballsitics research found a empirical correlation for pentrated thickness (for homogenous armor)for 1.4 crh projectiles in the order of an exponent of about 1.25 (if memory serves) this exponent had also an increased scope for penetration of 0.5-2.0 caliberarmor

[alecsandros]

According to Nathan's study, British 1920s cemented armor had 85% - 90% of the resistance to perforation of British post 1930 cemented armor, at best...

If this mean the ballistic limit was approximately 10% lower compared to german KCnA, Hoods facehardened armor had about 275mm effective thickness.

I got the same number,

What I don't understand is if the .85 - 0.9 figure is an average of resistance to various shell calibers (5" - 15") or if it is a specific value for large (BB) caliber shells.

This adds additional uncertainty...

[paul.mercer]

Paul

Gentlemen,
I'm sure this topic has been discussed before somewhere, but I could not find it, so appologies for reopening it.

Paul,

Don't know how you missed this - just a scroll down the current page in this subforum:

viewtopic.php?f=14&t=3877

Paul

Thanks, I've found it, what makes matters worse I even had a say in it, old age is catching up I'm afraid, sorry for reopening it.

[RobertsonN]

According to Nathan's study, British 1920s cemented armor had 85% - 90% of the resistance to perforation of British post 1930 cemented armor, at best...

If this mean the ballistic limit was approximately 10% lower compared to german KCnA, Hoods facehardened armor had about 275mm effective thickness.
on the basis of the gKdos 100 pentrationcharts, the compound angle for succesful perforations became ~40 degrees.

still some toughts on angular performance of a given projectiles. british post war ballistic experiments on the angular performance of high quality projectiles and plates showing differencies for the nominally equal projectiles.

For given speed, where shooting documents predicts perforation at 60 degrees, the interval in wich the first projectile penetrates at given velocity and the angle where approximately 100% of incomming projectiles pentrates, was approximately 10 degrees wide. So ther is always some degree of uncertainty.
Nevertheless the penetrtion documents gave good clue for the projectiles, but one must also consider the limits of these documents.

The german Gkdos 100 documents for the naval guns for instance tend to give to low pentrations as the impact velocity rises above 600 m/s
This is due to the high exponent of 1.6 used in the general formula. Because it is a monomial formula, it can hardly handle the varius failure modes/failure combinations of plate and projectile (What about rebound, shatter, and so on). Nevertheless it gave good clue for the performance of german projectiles according to statements of leading german ballisticians of the time.

For comparison the british post WW2 ballsitics research found a empirical correlation for pentrated thickness (for homogenous armor)for 1.4 crh projectiles in the order of an exponent of about 1.25 (if memory serves) this exponent had also an increased scope for penetration of 0.5-2.0 caliberarmor

I believe an inclination of 35 deg corresponds to an overall obliquity of 42 deg, 40 deg would be more like 46 deg.

Is the exponent you refer to the power to which v is raised in the penetration formula? Norman Friedman gave a value of IIRC 1.41 in his Battleship Design book and Nathan Okun has spoken recently of 1.21 in relation to some test data at relatively high striking velocities.

[Thorsten Wahl]

GkDos 100 formula



I have ported this formula to Excel and achieved the same charts as the german Gkdos 1000 dokuments predict. I had only to modify slightly the values from table 1.
Additional one has to consider that the originals charts were drawn with curve rules so deviations from charts created with excel should be usual.

The velocity dependend term is the sqrt(s^0.8) part therfor energy dependendent the 0.8 became 1.6

i have "experimented" with this formula an could achieve good agreement with US predictions if I use a exponent in the order of 1.25-1,3
aditional the obliquity part of the formula differ considerably from the F formula obliquity model and also from british Milne/Hilncliff model
the other models tend to predict too optimistic values for pentration.

so the possible "truth" is something in between these models.

For my part I would always prefer the original charts(with the limitations wich the model was known for.
except if someone can present the underlying datebase wich was used to create the charts and presents a better fitting model.

[Neil Robertson]

Sorry not to have picked up on this sooner. I was just involved in quite a big 'battle' on the other side, which may now have died down.

Yes, Eq. (1) does give S proportional to v to the power of 1.6 (which is high), provided one ignores to S dependence in the denominator of Eq. (1), which makes it very difficult analytically, as I recall when I tried to use it in 2011.

Looking back on the Hood it does seem surprising that the RN did not issue fighting instructions similar to those issued for German ships. And in the case of the Hood that should have included the importance of keeping the enemy in the case of the Bismarck at least 40 deg off the beam. That should not have been restrictive for engaging with 8 guns, because her turrets could all train to 60 deg off the beam (300 deg arcs). Employment with the POW may have been ackward though because her turrets could train to only 45 deg off the beam.

[Thorsten Wahl]

I was just involved in quite a big 'battle' on the other side, which may now have died down.

when I joined the navweaps forum in 2009 the attacks against me were more fierce, when I offered a view pro Bismarck . My name at this forum is "Thoddy", as well as at the Marinearchivforum.

I guess I was able to convince a lot of people with primary source data and information. I think the people wich insist for anything that Nathan Okun wrote, do more harm than good. I think Nathan Okun has pretty much knowledge on the theme and much more data than I have, but I am sorry that he is not participating on the discussion and he is obviously not ready to consider primary source information wich were contradicting his opinions and findings.

on the 1,6 theme i will answer later as I'm short on time.