Hood v Vittorio Veneto

[Alberto Virtuani]

Alecsandros wrote: "....Littorio class armor deck differed from centerline to outboard of ship: above machinery, the centerline armor was equivalent to ~ 107mm single sheet homogenous armor; outboard, it was equivalent to 98mm single sheet....... Furthermore, above magazines, Littorio had an equivalent of ~ 157mm armor, but on the outboard of the ship, adjacent to the magazines, the thickness was the same 98mm as above machinery. While some armored bulkheads could be in the way of a perforating trajectory......."

Hi Alec,
you are right about the inboard/outboard difference, but the scheme was a bit more complex/efficient. Here below the complete scheme and description of Littorio's horizontal protection over the citadel:
source E.Bagnasco, "Class Littorio Battleships", pag.37(scheme) and 58 (description).

As you see, the horizontal protection was based basically on 2 armor grade steel ("OD = acciaio omogeneo" Nickel - Chrome) decks (with some HT ("ER = Acciao ad Elevata Resistenza") steel backing them and a third intermediate HT deck).

Littorio_Scheme_1.jpg (98.67 KiB) Viewed 896 times

There was a weather deck ("Ponte di castello") of 36 mm Homogeneous + 9 mm HT steel (this was a de-capping deck), a middle deck ("Ponte di coperta") of 12 mm HT steel (I doubt this deck was improving protection, even marginally....) and a main deck ("Ponte di batteria") of 100 mm homogeneous + 12 HT steel over machinery (frame 83 to 130) inboard and 90 mm homogeneous + 12 mm HT steel outboard. Over magazines (frames 54 to 83 and 130 to 174) the main deck was 150 mm homogeneous + 12 mm HT inboard and 100 homogeneous + 12 mm HT steel outboard.

Even discounting at all the 33 mm HT steel...., Littorio's had a minimum armor grade horizontal protection over machinery of 136 mm homogeneous steel inboard and 126 mm homogeneous steel outboard, while over magazines it was 186 mm inboard and 136 mm outboard.

In addition there were several bulkheads ("Paratie Paraschegge") as thick as 36, 24 mm and 15 mm, contributing to the protection of the vitals close to the outboard area, while there was an upper belt ("Corazza di murata"), contributing to protect the outboard part at long-average ranges from shells with AoF of 35°of 70 mm KC vertical armor around and over the whole citadel.

In conclusion, while I agree with you about the potential "weakness" and discontinuity of the outboard part (5 to 7 meters large) scheme, I really wouldn't count on many crippling hits in a potential confrontation with QE's.....

Bye, Alberto

[Alberto Virtuani]

Dave Saxton wrote: In actual tests post war, no British battleship gun -including the 15"/L42- was able to penetrate more than 5" deck at ranges less than 32,000 yards."

Hi Dave,
Agree. More (even if one hit is not enough to statistically demonstrate anything) in real combat situation, the 15"/L42 shell of Warspite was anyway unable to penetrate Giulio Cesare vitals at Punta Stilo from around 24 km, despite this ship had a vulnerable horizontal protection of 110mm HT steel divided on 3 decks to which an armor of 25 mm was added during reconstruction for a total of 135 mm over machinery (and almost 160mm only over magazines). The shell hit a funnel base and exploded with heavy casualties over the main deck of 80mm, without penetrating it (but severing the uptakes and intakes to one of the two boiler rooms, that was evacuated, forcing speed to be reduced initially to 18 knots; later 2 boilers were relighted).....

Bye, Alberto

[alecsandros]

Hi Alec,
you are right about the inboard/outboard difference, but the scheme was a bit more complex/efficient. Here below the complete scheme and description of Littorio's horizontal protection (source E.Bagnasco, "Class Littorio Battleships", pag.35,37 and 58) over the citadel.

Hi Alberto,
I know the division of armor plates on Littorio class.
According to German research in the 30s and 40s,
Unless the divided plates are positioned within a particular distance from each other (to allow yaw effects to manifest fully), the division of armor between more plates was less effective then having a single plate of same thickness. 3 decks of 50mm each, positioned in relative proximity to each other were far , far , far less effective then a single 150mm deck.

For multiple sheets of armor in close proximitiy (including in direct contact with each otehr), the formula usualy employed is sqrt ( (deck 1)^2 + (deck 2)^2 + ... ).

Thus the end result is about 98mm effective thickness on outboard, 107mm effective above machinery and 156mm effective above magazines on centerline.

[alecsandros]

Dave Saxton wrote: In actual tests post war, no British battleship gun -including the 15"/L42- was able to penetrate more than 5" deck at ranges less than 32,000 yards."

Hi Dave,
Agree. More (even if one hit is not enough to statistically demonstrate anything) in real combat situation, the 15"/L42 shell of Warspite was anyway unable to penetrate Giulio Cesare vitals at Punta Stilo from around 24 km, despite this ship had a vulnerable horizontal protection of 110mm HT steel divided on 3 decks to which an armor of 25 mm was added during reconstruction for a total of 135 mm over machinery (and almost 160mm only over magazines). The shell hit a funnel and exploded with heavy casualties over the main deck of 80mm, without penetrating it (but severing the uptakes and intakes to one of the two boiler rooms, that was evacuated, forcing speed to be reduced initially to 18 knots; later 2 boilers were relighted).....

Bye, Alberto

... British APC projectiles had typical fuze delays working to around 0.025 seconds from initial fuze, with typical variations down to 0.020 and up to 0.035 sec, IIRC.
This gives a 400m/s projectile (fuzed) exploding after traveling 8 to 14 meters from position of fuzing. I suppose that's about where it exploded on Caesare ?

[Alberto Virtuani]

@Alecsandros:
Hi Alec,
re. horizontal protection: the 2 "minimum" armor decks outboard (36 and 90 mm) are not in close proximity, they are separated by 2 levels in the ship, exactly as in e.g. Bismarck and Richelieu (1 deck distance) class . Would these latter have the same limited protection against plunging fire and bombs ?
Adopting your formula for the Bismarck over machines (as per this site scheme) gives an horizontal protection of just 94 mm for the whole area against plunging shells..... albeit supplemented by a stronger side armor of 145 mm against relatively short range shells.....

On Littorio's there is anyway the 70 KC vertical armor that contribute to horizontal protection of the "weaker" outboard area at long-average ranges......

I agree a single deck is more efficient than multiple ones of the same total width , but not up to this point.......

Contradicting German conclusions, the 2 vertical (inclined) plates of the main belt (70+280mm, these ones clearly in close proximity) demonstrated to work very well in the tests performed by Italians before the war, and thus it was decided to adopt them for the Littorio's.



re: hit on Cesare, I personally suspect that the shell did not work correctly, burning in advance, before reaching the main deck, but I'm not sure as I have not found a complete damage report for Cesare. For sure, the shell did not penetrate the vitals.

Bye, Alberto

[Dave Saxton]

It was actually the British who stressed that two plates in direct contact with each other did not provide an effective thickness of the sum of the two plates and actually provided less effective thickness than if the plates were spaced. One can see this in the official specifications of the KGV class. The effective horizontal protection claimed is 127mm over the machinery and 150mm over the magazines. These are the thickness of the actual armour plates laid over the top of the structural steel of the decks. As far as the Admiralty was concerned the deck structures and the weather deck and the splinter deck accounted for nothing to the effective deck protection. The same for turret armour and belts in direct contact to the underlying ship's structure.

This was fairly well known world wide, although the British attained actual test data to support it. For example, the IZ of North Carolina was 18,000 yards to 28,000 yards vs the new American 14"/50 gun. This requires a deck protection of only 105mm. The main armoured deck on NC was 88m STS inboard and 102mm STS outboard laid over the 36mm STS structure. The 36mm structure accounts for little in the USN calculations. There is evidence that the 38mm weather deck was considered a yaw inducing deck but once again it is not accounted for much in the calculations. All this STS layered is not very weight or cost efficient but it was what the structural engineers apparently wanted.

The German (actually Krupp's) findings (and vindicated by British studies post war) that two spaced decks can provide an effective thickness at least equal to sum thickness of the two plates is based on very specific design principles. It is not just any spaced plates arrangement. The quality and/or the effective thickness of the main plate must be well above standard. What makes this possible in part is de-capping and yaw becoming fully manifest. A wide interspace is essential to this design. Thus the German designs used only two widely spaced decks of armour grade steel not laid over a structural component. The armour plates performed both ballistic and structural roles. This is of course very efficient in terms of weight, which was apparently a primary design priority. The non ballistic deck in between (to use G&D's term) was only 6mm structural steel so as not to up set the yaw becoming fully manifest.

The Italian use of only 12mm on their in between deck probably was for the same reasons. The Italian belt not having a large interspace is not necessary in contradiction to the German findings, because it was designed to destroy incoming rounds, rather than stop them by providing a larger effective thickness.

[Alberto Virtuani]

Dave Saxton wrote: "The non ballistic deck in between (to use G&D's term) was only 6mm structural steel so as not to up set the yaw becoming fully manifest. "

Hi Dave, thanks for the very clear explanation. However, wasn't the "non-ballistic", intermediate deck of Bismarck a 20 (or even a 24) mm one as per this very site technical description ?

Bye, Alberto

[Dave Saxton]

Dave Saxton wrote: "The non ballistic deck in between (to use G&D's term) was only 6mm structural steel so as not to up set the yaw becoming fully manifest. "

Hi Dave, thanks for the very clear explanation. However, wasn't the "non-ballistic", intermediate deck of Bismarck a 20 (or even a 24) mm one as per this very site technical description ?

Bye, Alberto

According to official drawings -6mm.

[dunmunro]

The Littorio class would be extremely vulnerable to diving hits that could easily pass under their shallow belts. A diving hit such as the hit on Bismarck might imperil a magazine but could also cause massive flooding within the Littorios undivided machinery spaces.

A 1942 scenario would see the QEs equipped with gunnery radar including a combined warning/gunnery centimetric radar.

[Alberto Virtuani]

@Dunmunro:
Hi Duncan,
I agree about the belt of Littorio's being very shallow and this would have posed some risks. They were however designed for Mediterranean seas and very limited range, so there was not much waterline level change to be taken into account.....
On the other side, the QE's would be exposed to Littorio's hits at any "height", under and over waterline, due to their lack of any IZ vs the Italian 15", at all practical ranges.

Radar is a great tactic advantage in general, but not so much in a battle to the death going to a very short range, as per this proposed scenario.

Bye, Alberto

[dunmunro]

@Dunmunro:
Hi Duncan,
I agree about the belt of Littorio's being very shallow and this would have posed some risks. They were however designed for Mediterranean seas and very limited range, so there was not much waterline level change to be taken into account.....
On the other side, the QE's would be exposed to Littorio's hits at any "height", under and over waterline, due to their lack of any IZ vs the Italian 15", at all practical ranges.

Radar is a great tactic advantage in general, but not so much in a battle to the death going to a very short range, as per this proposed scenario.

Bye, Alberto

There is about the same probability of an RN 15in shell diving under Littorios' belt as there is in actually hitting the belt. It would appear that the magazines of Littorio could be entered directly by a shell striking the water just short of the main belt and diving under it. The 14in shell from PoW that passed under Bismarck's belt burst near the junction of two transverse bulkheads causing immediate flooding of the forward inboard compartment (and one more inboard of that) and slow flooding of the boiler room abaft the after transverse bulkhead. However flooding was limited because of the number of longitudinal bulkheads on Bismarck (the rebuilt QEs are similar). A similar hit on a Littorio would flood one entire transverse machinery space and cause flooding into another - such a single hit would severely cripple the target ship.

Certainly there is a much greater probability of a RM 15in shell penetrating even the 13in portion of a QE belt, than of an RN 15in penetrating Littorio's belt but it would be wrong to say that penetration of QE's belt is certain because in actual combat target obliquity would often be much greater than 40 degs where the 13in belt would probably defeat an RM 15in shell at typical target ranges. Additionally the 5in main armoured deck (MAD) on a QE is quite low and many trajectories that defeat the main belt will see the shell striking the MAD rather than entering a magazine or machinery space.

[Alberto Virtuani]

Dunmunro wrote: "There is about the same probability of an RN 15in shell diving under Littorios' belt as there is in actually hitting the belt.............but it would be wrong to say that penetration of QE's belt is certain because in actual combat target obliquity would often be much greater than 40 degs...... "

Hi Duncan,
I agree that everything can happen ina n hypothetical naval scenario......
However,underwater hits (from a shell not designed to work properly underwater....) very seldom explode (see the German 15" that penetrated PoW at DS). At short range, a shell should travel underwater some 10 meters to be able to pass under the 2 meters deep (4,4 meters total height) belt of Littorio's and other 7 meters to pass the Pugliese cylinder system to reach the final bulkheads.... I would not rely only on a lucky (activating) underwater hit to win this battle, as statistically they are they rare (exception was at DS....).

In this proposed scenario the fast approach of Littorio's to close range would be directly on the British line with an angle of 20 to 30 degrees to keep aft turrets bearing, therefore striking angle very close to 90°. Once at short range (well under 20 km), a classical broadside duel would provide 90° striking angle to shells. QE's had no sufficient speed to impose any other combat situation to the Littorio's.

I think it's a very unwise tactic to put a ship without IZ against another that have, as DS well demonstrated.

Bye, Alberto

[Alberto Virtuani]

Dunmunro wrote: "....the 5in main armoured deck (MAD) on a QE is quite low and many trajectories that defeat the main belt will see the shell striking the MAD rather than entering a magazine or machinery space."

....... just to add that the problem is not the 5" MAD (that would have defeated the shell when it pass through the belt well above waterline), but the 2" HT slope (with a steep angle anyway as Dave has pointed out) that was not improved at all during modernization.

Any hit passing the belt ,close enough to waterline, had a free path to magazines and machinery. This was the flaw of QE's armor scheme vs a modern gun, the same that possibly doomed the Hood at the DS.

Bye, Alberto

[slaterat]

The ace in the hole for the QE"s is the 15 /42. It's battle tested, faster firing , more accurate and has a bursting charge twice as large as the Italian 15/50. It seems to me that all of the high velocity big guns have inconsistency when it comes to accuracy. If the Italians want to make it a close action they will be the ones facing withering gunfire. I think the Italians would be better off keeping the distance long and hoping to get a magazine hit. The citadel and engine rooms are fairly safe on the Littorios , so if they start to take upper damage, to guns turrets, command and control ect ,then they could safely retire.

Slaterat

[alecsandros]

Dave Saxton wrote: "The non ballistic deck in between (to use G&D's term) was only 6mm structural steel so as not to up set the yaw becoming fully manifest. "

Hi Dave, thanks for the very clear explanation. However, wasn't the "non-ballistic", intermediate deck of Bismarck a 20 (or even a 24) mm one as per this very site technical description ?

Bye, Alberto

According to official drawings -6mm.

... I have some drawings with 20mm as well (St52 construction steel), but only on the centerline of the ship, maybe 2 meters right and left from the center. That is different form the 6mm deck.