Danger space, hitting space

[tommy303]

Let me rephrase the definitions:

Danger space by definition is any point between the lowest part of the ship and the highest point of the ship that is liable to be struck by a shell within a particular set of angles of descent. It concerns not only the vertical aspects of the target, but the horizonatal as well as it accounts for any strike in between waterline and foretop regardless of whether or not the strike is against vertical or horizontal surfaces.

Hitting space on the other hand, concerns only those areas where a hit from a shell at particular angles of descent will produce a strike measured through the waterline of the target, ie from one side of the target to the other. At close ranges danger space is generally wider than hitting space, but at extreme ranges the two are almost identical because of the steep angle of trajectory.

[José M. Rico]

This drawing will help illustrate these concepts.



_ Ballistic data as taken from: http://www.kbismarck.com/38cm.html

[Bgile]

Yes, although your drawing shows only hits above the waterline and doesn't include the superstructure, it does illustrate the concept.

My point was that since Bismarck's vitals are immune to hits on her main belt, the only way to get into them is to hit the relatively small area represented by the panzerdeck, or get below the belt as PoW did.

Obviously you can put turrets and FC out of action and wreck the unarmored areas as the British did in the final engagement, but you can't penetrate the vitals of this ship unless you can penetrate the deck armor.

[tommy303]

This also provides a graphic representation of the two concepts:

[Karl Heidenreich]

Guys,

thanks for the graphics. They help a lot.

[lwd]

...My point was that since Bismarck's vitals are immune to hits on her main belt, the only way to get into them is to hit the relatively small area represented by the panzerdeck, or get below the belt as PoW did.....

Wait a minute. I thought only part of her "vitals" were possibly immune.

[Bgile]

...My point was that since Bismarck's vitals are immune to hits on her main belt, the only way to get into them is to hit the relatively small area represented by the panzerdeck, or get below the belt as PoW did.....

Wait a minute. I thought only part of her "vitals" were possibly immune.

I believe Nathan Okun's calculations showed that belt + scarp + armored bulkhead was not penetrable by anything except one of Yamato's guns at range = 0. My impression is this was true for the entire length of the citadel.

[nathanokun]

"Danger space" is the hull that can be hit at and above the waterline (upper hull side from the waterline up and the weather deck), though a downward-moving shell can hit the below-deck area sometimes, particularly at a high angle of fall. This puts reserve buoyancy and engine/boiler rooms (most extend up somewhat above the waterline) in direct danger of penetrating hits. This is where an "over" hit in the "shadow" of the ship behind it would be stopped by running into the ship structure (usually limited to the hull in most charts) first, on top of those hits that would run into the hitting space when they hit on the near-side of the hull (hull width) -- shadow + hitting space (hull width from the side) = danger space.

"Hitting space" is that hull horizonal area **at the waterline** that can be hit by the same shell, so it is smaller at closer ranges than the danger space -- this is what would put below-the-waterline gun magazines in danger at the given range. Thus, it is always the hull width against an enemy on your ship's broadside and hull length against an enemy firing over the bow or stern (much larger, so raking fire is not a good thing to be on the receiving end of!). Hitting space is thus a subset of the total danger space. The USS MONITOR, other than the turret and small conning tower, would essentially ALWAYS have the hitting and danger spaces essentially the same, since the hull's weather deck is only a few inches above the waterline.

The 32cm vertical KC n/A side armor (on top of about 2.5cm of Shipbuilding Steel 52 (high tensile steel) hull plating and a 10cm teak cushion; slightly tilted outboard in the bow region) backed up by the 11cm (12cm alongside TIRPITZ magazines, I think) sloped Wh armor deck at 68 degrees from the vertical is more-or-less proof against any shell hitting this pair of plates from the side at any range. Penetrating the belt with an undamaged projectile will cause it to be tilted up somewhat horizontally from its original angle of fall, so that the impact on the sloped deck is usually over 70 degrees, which makes that plate VERY difficult to penetrate with any projectile slowed down by the main belt first. My computations showed nobody could penetrate it, but I did not try every possible gun and shell, so it might be possible at very close range for some gun, but that is unlikely to happen unless BISMARCK/TIRPITZ is already smashed up.

The 14.5cm KC n/A upper hull (on the same backing) starts high enough on the hull that only at an extended range -- and thus lower striking velocity -- would the sloped deck be hit after hitting this thinner belt armor, so this does not give any real improvement on being able to penetrate this sloped region. The 14.5cm upper belt and 8cm Wh near-waterline flat armored deck (11cm/12cm over the magazines for BISMARCK/TIRPITZ, respectively) is also difficult to penetrate, especially as the fuze delay in most shells would stop the shell -- break it mostly into pieces when the filler goes off -- between the two plates in most cases (other than a dud, a defective delay element with an over-long delay, or a Japanese "diving" Type 88/91 AP shell with its super-long fuze delay).

The 5cm Wh weather deck (perhaps 8cm in reinforcing rings around the main barbettes, but I do not have details) spaced about 6.5m above the armored deck gives kind of a thin total deck in purely penetration terms, but the long distance also gives most delay-action fuzes time to destroy the shell prior to hitting the main armor deck when colming in from the side at a shallow angle, so again the chance of penetrating this is not good for a non-Japanese properly-functioning shell. Thus, you have to be firing at a very long range so that the shell is coming down very steeply to allow the distance after hitting the weather deck to get small enough to allow most APC shells to reach the lower armored deck intact in the first place. Note, though, that you get the upper hull smashed up right down to the waterline in the hit region for virtually ALL hull hits even if the main armored deck stops the damage beneath it, so these ships are losing a lot of reserve buoyancy against any hull hit whatsoever to try to protect their lower hull from plunging fire.

Note that firing over BISMARCK/TIRPITZ bow or stern in raking fire eliminates most of this added layered protection (no sloped deck, no thick main belt (just a single vertical transverse bulkhead of reduced thickness), hull plating thin enough in front of the transverse bulkhead armor that the base fuze of most large shells may not be set off until the armor itself is reached, etc.), so BISMARCK/TIRPITZ lower hull is MUCH more vulnerable at any range from the bow or stern. This is somewhat true for most battleships, but the difference is MUCH bigger for these German ships!!

Nathan Okun

[RF]

I seem to recall that in Ballard's book (I can't remember the precise detail's) that there was one hit from Rodney which did pentrate the main armoured belt, evidenced by a huge hole at the point the 16 inch shell struck. From memory I think it was said by one ballistic's expert that the hit occured at a moment the ship pitched at an angle because of the rough swell to cause the penetration that otherwise would not have happened.

[José M. Rico]

RF.- Yes, I think there are at least 2 penetrations on the main belt in the wreck, but note that Nathan Okun is referring to the combo 32cm main belt + 11cm sloped deck. 16 inch shells from Rodney could defeat Bismarck's main belt at the range she was engaging, but it is very unlikely they would pass through the sloped deck too.

By the way, thank you for stopping by the forum Nathan!

[Thorsten Wahl]

Nathan Okun
Note that firing over BISMARCK/TIRPITZ bow or stern in raking fire eliminates most of this added layered protection (no sloped deck, no thick main belt (just a single vertical transverse bulkhead of reduced thickness), hull plating thin enough in front of the transverse bulkhead armor that the base fuze of most large shells may not be set off until the armor itself is reached, etc.), so BISMARCK/TIRPITZ lower hull is MUCH more vulnerable at any range from the bow or stern. This is somewhat true for most battleships, but the difference is MUCH bigger for these German ships!!

First of all, Thank you for your comprehensive work on penetration.

Did you take in account that the hull at the bow was made from 60 mm Wh and also at the bow from 80 mm Wh. Theoretical in this strenght Wh should be able to set off almost every fuse.

Sorry for my bad english.

[Byron Angel]

Thorsten, your English may not be perfect in every single detail, but it is extremely good IMO. You owe no apologies whatsoever.

Byron

[José M. Rico]

Did you take in account that the hull at the bow was made from 60 mm Wh and also at the bow from 80 mm Wh. Theoretical in this strenght Wh should be able to set off almost every fuse.

Sorry for my bad english.

Yes, there was a 60 mm Wh belt forward with an outboard inclination of about 17º abreast turret Anton.
Also don't forget the 50 mm upper deck.

Your English is OK.

[Bgile]

A shell could come in from the bow area and hit only the 220mm armor plate before entering the forward magazine. This is similar to most of her contemporaries.

[José M. Rico]

A shell could come in from the bow area and hit only the 220mm armor plate before entering the forward magazine.

Possible, but unlikely. In most cases a shell would have to go through the upper deck or splinter side belt first.