Why no turtleback?

[TTTT]

The Germans really liked their turtleback armor, which they used in all their big ships. This can also be seen in the never built H-class battleships, which would have had a slightly thicker turtleback and slightly thinner main belt.

The heavily angled 110-120mm scarp behind the main belt certainly added a lot to the total, effective side armor of Bismarck, which was thicker even than Yamato.

But what was the reason other nations, like Great Britain, dropped it in their new battleships?

Weight? Space?

[marcelo_malara]

The Germans really liked their turtleback armor, which they used in all their big ships. This can also be seen in the never built H-class battleships, which would have had a slightly thicker turtleback and slightly thinner main belt.

The heavily angled 110-120mm scarp behind the main belt certainly added a lot to the total, effective side armor of Bismarck, which was thicker even than Yamato.

But what was the reason other nations, like Great Britain, dropped it in their new battleships?

Weight? Space?

Well, the armoured deck of the KGV class was the upper deck, exposed to the weather, a turtleback would give the ship the aspect of the subs or of an old destroyer.

[TTTT]

No, as far I can see KGV's main armor deck were where Bismarck's battery deck were, below the 1-inch weather deck.

Hood had a similar placement, but turtleback,albeit thinner than Bismarck's.

[marcelo_malara]

No, as far I can see KGV's main armor deck were where Bismarck's battery deck were, below the 1-inch weather deck.

Hood had a similar placement, but turtleback,albeit thinner than Bismarck's.

My mistake, I was interpreting the next deck up as a forecastle, which KGV did not have.

[marcelo_malara]

I think that to have a turtle back you need that the belt reaches one deck higher than the level of the armoured deck, if not an incoming shell would impact directly the slope without passing thru any armour. In the KGV the belt does not extend further up the amoured deck, whereas in Hood and Bismarck does.

[TTTT]

Yes, that's a good explanation.

Interesting to see that also Richelieu has slopes, but not on her main deck.

[marcelo_malara]

Yes, that's a good explanation.

Interesting to see that also Richelieu has slopes, but not on her main deck.

Interesting too is her thickness of 150/170mm on the main deck.

[Cag]

Hi All,

As has already been said the KGV class had its armour on the main deck laid above and between the forward and aft transverse bulkheads, mated to the side armour to create an armoured box.

However there was additional side, and more importantly for this discussion, deck armour on the lower deck forward and aft of these bulkheads to protect the magazines from splinters and also to cover the steering gear aft.

These did have a slope at their edges similar to a turtleback, for example in the Prince of Wales damage report one of the shells that hit aft penetrated the ships side, partially exploded and the nose of the shell ricocheted off the sloped part of this armour and back out of the ships side exiting further aft.

Hope that helps a wee bit,

Best wishes
Cag.

[Mostlyharmless]

The advantage for the RN, USN and IJN of having a high main armour deck was that you could have a large protected volume with a shorter citadel which allowed you to have thicker belts and a thicker main armour deck. This made sense to the British as they wanted to make devastating single hits as unlikely as possible as they remembered the three battlecruisers lost at Jutland.

The Germans wanted to have the longest citadel possible because they remembered Lutzow sinking due to flooding forward and thus they were happy to go with four turrets. The fate of Musashi suggests to me that the KM was not being totally unrealistic. They may even have found a way to use decapping and yaw to protect from fairly long range shell hits (note may). However, the bomb hits on Scharnhorst at La Pallice revealed that their scheme didn't work against bombs.

[marcelo_malara]

The advantage for the RN, USN and IJN of having a high main armour deck was that you could have a large protected volume with a shorter citadel which allowed you to have thicker belts and a thicker main armour deck. This made sense to the British as they wanted to make devastating single hits as unlikely as possible as they remembered the three battlecruisers lost at Jutland.

The Germans wanted to have the longest citadel possible because they remembered Lutzow sinking due to flooding forward and thus they were happy to go with four turrets. The fate of Musashi suggests to me that the KM was not being totally unrealistic. They may even have found a way to use decapping and yaw to protect from fairly long range shell hits (note may). However, the bomb hits on Scharnhorst at La Pallice revealed that their scheme didn't work against bombs.

HI. I do not understand this, why a higher armoured deck means a shorter belt? The belt has to protect the sides of magazines as well as the machinery, what you said only makes sense if the machinery space is shorter due to being higher, but that would mean it protruding above the water line, what is not a good idea.

Regards

[Steve Crandell]

HI. I do not understand this, why a higher armoured deck means a shorter belt? The belt has to protect the sides of magazines as well as the machinery, what you said only makes sense if the machinery space is shorter due to being higher, but that would mean it protruding above the water line, what is not a good idea.

Regards

It seems obvious to me. If you move the armor deck "up" in the ship, then more weight must be devoted to the belt armor which must reach higher in the ship to meet the armor deck. This means there is less weight to devote to extending the armor belt to areas outside the citadel.

[Mattzo]

Hi All,

As has already been said the KGV class had its armour on the main deck laid above and between the forward and aft transverse bulkheads, mated to the side armour to create an armoured box.

However there was additional side, and more importantly for this discussion, deck armour on the lower deck forward and aft of these bulkheads to protect the magazines from splinters and also to cover the steering gear aft.

These did have a slope at their edges similar to a turtleback, for example in the Prince of Wales damage report one of the shells that hit aft penetrated the ships side, partially exploded and the nose of the shell ricocheted off the sloped part of this armour and back out of the ships side exiting further aft.

Hope that helps a wee bit,

Best wishes
Cag.

Just to add to this, this profile shows the armour layout of the King George V class, with the 'turtleback' aft.




This photo of Duke of York under construction shows the layout clearly - there is the flat deck immediately aft of the citadel, and then the 'turtleback' which covers the shafts and steering gear.

[Mostlyharmless]

What I meant was that the designers wanted to have a certain volume of citadel protected from shells. Having the main armour deck higher enabled them to get the same volume with a shorter citadel. Thus Bismarck had a citadel of around 70% of the ship's length whereas at the other extreme South Dakota and Yamato had citadels of around 53% (I haven't actually checked recently) of the length. This obviously allowed thicker total deck armour with those designs. KGV and Vanguard show a compromise. However, Vanguard has more protected volume than Bismarck despite a shorter and narrower citadel.

The issue of belt weight is more complicated. The main belts of Bismarck, KGV and South Dakota all go up to one deck below the weather deck (South Dakota saves weight at the expense of being a little wet). Bismarck could have a thinner belt than KGV because of the scarp but has an upper belt, which costs weight but allows a saving in the weight of the barbettes. The failure to extend the belt deep enough was a weakness that would be addressed in the H39 design.

[marcelo_malara]

What I meant was that the designers wanted to have a certain volume of citadel protected from shells. Having the main armour deck higher enabled them to get the same volume with a shorter citadel. Thus Bismarck had a citadel of around 70% of the ship's length whereas at the other extreme South Dakota and Yamato had citadels of around 53% (I haven't actually checked recently) of the length. This obviously allowed thicker total deck armour with those designs. KGV and Vanguard show a compromise. However, Vanguard has more protected volume than Bismarck despite a shorter and narrower citadel.

The issue of belt weight is more complicated. The main belts of Bismarck, KGV and South Dakota all go up to one deck below the weather deck (South Dakota saves weight at the expense of being a little wet). Bismarck could have a thinner belt than KGV because of the scarp but has an upper belt, which costs weight but allows a saving in the weight of the barbettes. The failure to extend the belt deep enough was a weakness that would be addressed in the H39 design.

I have no plans of Yamato. In the case of South Dakota, your number of citadel/LOA is correct at about 53%. In the case of Bismarck I measured it at about 63%. But, you are overlooking that South Dakota has three turrets, and if I add just the length of one barbette, 10 m, then citadel goes up to about 60% of the LOA, no much shorter than Bismarck´s.

I disagree with your statement of pure citadel volume, because the volumes that the citadel mainly protects (magazines and machinery) can not be made shorter and higher for the same volume, as I said the limit of height is the water line, about 10 m from the bottom of the ship. Those protected volumes are constrained in beam and height, so the only variable you have to accommodate them is length.

Regards

[Mostlyharmless]

I had a 170.7 metres citadel of 241.5 metres at waterline or 70.7% but it is less if you use the overall length from https://www.kbismarck.com/proteccioni.html.