Battleship Vittorio Veneto

From the Washington Naval Treaty to the end of the Second World War.
RobertsonN
Member
Posts: 197
Joined: Wed Jan 05, 2011 9:47 am

Re: Battleship Vittorio Veneto

Post by RobertsonN » Wed Feb 22, 2012 10:59 pm

The other figures for deck penetration of the 15/50 that were given in that September 1942 document
(and for which there is no obvious ambiguity due to misprints) are: 67 mm @ 19000 m, 74 mm @ 20000 m, 105? mm @ 24000 m and 124 mm @ 26000 m. A lighter 824 kg SAP shell with a 20 m/s higher MV of 870 m/s gave somewhat lower figures: 61 mm @ 19000 m, 68 mm @ 20000 m, 97 mm @ 24000 m and 114 m @ 26000 m.
Different (probably earlier) figures given from O.T.O. Melara were: 73 mm @18000 m and 130 mm @ 28000 m.
The author comments that the Sep. '42 figures are probably for a lower muzzle velocity (elsewhere it is stated that an MV of 870 m/s was intended for the 885 kg AP but that this was reduced to 850 m/s to reduce dispersion at longer ranges) and more conservative (they give lower vertical penetrations).

alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Battleship Vittorio Veneto

Post by alecsandros » Thu Feb 23, 2012 6:54 am

Dave Saxton wrote:
Some factors to consider here:
1) The angle of fall at this range of the high velocity Italian 15" means that the shell is striking 72* from the normal. Striking at the normal it takes homogenous armour 20% the caliber to effect de-capping, but as the striking angle becomes more acute it requires less thickness.
But it's not about 15" shell. It's about 16" shell (which, btw, I didnt' know was ever comissioned in the Italian Navy ?).

The point I was making above was exactly angle of fall: it's one thing to decap 16" shell @ 18* AoF (assuming it existed), and another to decap a 16" shell at 25* AoF. Firing distances are the same... (~ 26.000y for US 16"/L45 and British 16"/L45, and the supposed Italian 16"/L50...)
2) The total thickness of the de-capping plate is more than 36mm.
It's 36mm AOD + 9mm ER, IIRC. USing the square root function, we get ~ 37.5mm effective. Nathan gives it an "effective" thickness of 42mm. Even taking Natha's figure, this is about ~10% of the diameter of a 16" shell, half of the usual 20% figure mentioned for complete decapping...

On the other hand, Italian homogenous armor is not at all so well-known to me. I only have Nathan's armor comparison paper on it.
So maybe it worked as mentioned above... Who knows ?
Yet, for the time being I am a bit skeptical about figures significantly better than US STS and German Whotan.

RobertsonN
Member
Posts: 197
Joined: Wed Jan 05, 2011 9:47 am

Re: Battleship Vittorio Veneto

Post by RobertsonN » Thu Feb 23, 2012 11:15 am

The book does not say a 16 in shell was used but that one was simulated, however that was done.

At 18 deg angle of fall, the virtual thickness of a 36 mm deck is about 116 mm.

As importantly, for this very oblique impact, the force acting upwards on the cap is all on one side of the cap, which intuitively makes it easier to knock off. At normal impact the reaction of the armor is pushing the cap back symmetrically on the shell.

User avatar
Dave Saxton
Supporter
Posts: 3093
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: Battleship Vittorio Veneto

Post by Dave Saxton » Thu Feb 23, 2012 3:01 pm

alecsandros wrote:It's 36mm AOD + 9mm ER, IIRC. USing the square root function, we get ~ 37.5mm effective. Nathan gives it an "effective" thickness of 42mm..
That's true as far as energy comsumption or resistance to penetration, but what about the ability to de-cap?
The point I was making above was exactly angle of fall: it's one thing to decap 16" shell @ 18* AoF (assuming it existed), and another to decap a 16" shell at 25* AoF.


25* AoF is still 65* from the normal, so still rather acute.
On the other hand, Italian homogenous armor is not at all so well-known to me. I only have Nathan's armor comparison paper on it.
So maybe it worked as mentioned above... Who knows ?
The properties required for best performance in a de-capping array are not necessarly the same as needed for a single plate. For one thing, higher elongation % or ductilty may not be the best indicator of armour quality in a de-capping array (not that is otherwise in all cases). As tensile strength increases, hardness also increases, but ductility is reduced. However, increased hardness and tensile strength works better against un-capped projectiles at resisting penetration.

I have the chemistry and mechanical properties of AOD and ER filed away somewhere. AOD and ER were vanadium based alloys rather than a nickel/chrome alloy, or chrome/moly alloy. I don't think this is necessarly a bad thing and may have been better. The HY steels adopted by the USN after WWII to replace STS are very much like ER and AOD. The main draw back is that vanadium based alloy steels are difficult to weld properly and do not like to be heat cycled.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Battleship Vittorio Veneto

Post by alecsandros » Fri Feb 24, 2012 10:16 am

I took a closer look on Nathan's decapping revisited, which takes into account some 320mm APC shell tests done versus a mock-up version of Vittorio Venetto.

Our situation:
upper-deck: 36mm AOD + 9mm ER. The compound would have 45mm, while the laminate would have an effective thickness of 37.5mm, if using the sqrt formula.

The attack would be made by 16" (406mm) APC shells, striking at acute (60-80*) obliquity. But what kind of shells ?

Looking at
http://www.navweaps.com/index_tech/tech ... ap_pic.jpg

we see that the most common APC shells used in the war were Type 1 and Type 2 hard-capped shells. German and US naval shells were usualy type 2, with all other navies probably using type 1's.

Thus, the impact of a 406mm shell over the armor deck would be placed into one of the following categories from the drawing:

1) IF we consider the sqrt formula for the laminate, then T/D = 0,09 and for 60-80* obliquity we are in the blue area. "only type 1 projectile cap knocked off"
2) IF we consider the compound of 45mm thickness, T/D = 0,1108, and we're still in the blue area, albeit closer to the orange border ("50% chance of type 2 projectile cap knocked off")

===
So, I guess the results are confirmed by this drawing, because the Regia Maria was using Type 1 shells, decappable, apparently, by this armor at this obliquity.
On the other hand, I don't think the 36+9mm laminate could decap an American superheavy shell, or a German 380mm shell, even at very high obliquity from the normal.

delcyros
Member
Posts: 213
Joined: Mon Feb 07, 2011 9:26 pm

Re: Battleship Vittorio Veneto

Post by delcyros » Fri Feb 24, 2012 10:30 am

Acc. to Nathan Okun, all USN APC, except a single batch of 6in APC and US Army APC (not used on battleships) were type 1 capped.

RobertsonN
Member
Posts: 197
Joined: Wed Jan 05, 2011 9:47 am

Re: Battleship Vittorio Veneto

Post by RobertsonN » Fri Feb 24, 2012 11:27 am

Italian AP shells were pointed, which gave them a good performance against vertical armor (because the shell could dig well into the armor while removing much less armor than for a blunt nosed shell, i.e. early on low energy is required in relation to penetration into the plate) but rather poor horizontal penetration (tendancy to scope, as pointed out by Dave Saxton; here it is a blunt nosed shell that requires lower energy for a given distance into the plate).
For near normal impact, the cap is pushed back onto the shell and cap removal can really only take place by breaking up the cap, which unless it is brittle will require considerable energy expenditure. For oblique impact, the cap is acted on asymmetrically and cap removal may require only breakage of the joint or fixing to the shell.This process requires much less energy than the process near normal impact. If the shell is very blunt, as in the csae of US shells, breakage of the fixing will probably be sufficient for cap removal. However, for Italian and other pointed shells, the head of the shell still offers the cap considerable support even after the fixing has been broken so that the cap is more difficult to remove at oblique impact.

The Italians designs used spaced systems to take advantage of decapping. This being the case, it may be that one reason they chose pointed shells was to make them more difficult to decap. The Americans sources contain no indication that they considered decapping. They used thick AON sytems and chose blunt shells to maximize penetration of thick horizontal armor.

Bagnasco says that after the War the Italians found out that the Americans had more efficient machinery and that their ship fittings were lighter than corresponding Italian ones, which allowed more weight to be used for military characteristics. Only after 1943 did the Americans show much interest in decapping.

The historical sources contain no classification of caps as type 1 or 2. This is a recent suggestion. US shells were probably the easiest to decap at oblique impact beacuse their blunt heads offered little support to their caps. The Italians did test their protective deck layout in 1935. There is no evidence that the Americans, despite their much greater resources, ever tested theirs either against shells or bombs.

alecsandros
Senior Member
Posts: 4349
Joined: Wed Oct 14, 2009 2:33 pm
Location: Bucharest, Romania

Re: Battleship Vittorio Veneto

Post by alecsandros » Fri Feb 24, 2012 11:54 am

Nathan himself presented doubts about the final conclusions of decapping revisited. After all, there weren't so many tests (or not enough are known to us today) done at the time so as to draw clear-cut conclusions.


@Delycros,
There were no US battleship guns present in the tests taken into consideration by Nathan in his "decapping revisited" thread. That doesn't mean they were all type 1...
And there is at least 1 example that shows very good horizontal performance of 16" US BB shell:
The 2x16" shells from Massachussets against Jean Bart functioned pretty god damn well at acute obliquity (65* from the normal IIRC), and passing through multiple layers of armor decks (allthough not at the correct spacing, and probably not quality). The first shell passed 22+150+40mm of armor, and than exploded in the empty 150mm magazine. The second passed 16+16+13+100mm of steel (allthough probably not of armor grade material), and than exploded inside a ballast tank.
It is my impression that without retaining the caps, the shells couldn't have functioned properly...

@RobertsoN

I don't know if the USN conducted decappign tests pre-war. HOwever, their fast battleships had multiple levels of armor decks, indicating that they must have taken into consideration the degradation of shell performance when striking multiple, correctly-spaced armored planes. This is underlined by the yaw tests doen pre-war by the USN...

delcyros
Member
Posts: 213
Joined: Mon Feb 07, 2011 9:26 pm

Re: Battleship Vittorio Veneto

Post by delcyros » Fri Feb 24, 2012 2:45 pm

@Delycros,
There were no US battleship guns present in the tests taken into consideration by Nathan in his "decapping revisited" thread. That doesn't mean they were all type 1...
And there is at least 1 example that shows very good horizontal performance of 16" US BB shell:
The 2x16" shells from Massachussets against Jean Bart functioned pretty god damn well at acute obliquity (65* from the normal IIRC), and passing through multiple layers of armor decks (allthough not at the correct spacing, and probably not quality). The first shell passed 22+150+40mm of armor, and than exploded in the empty 150mm magazine. The second passed 16+16+13+100mm of steel (allthough probably not of armor grade material), and than exploded inside a ballast tank.
It is my impression that without retaining the caps, the shells couldn't have functioned properly...
You have probably noticed that Nathan Okun seperated the types not according to their performance but according to cap attachment. Krupp and US army APC had very different cap attachments and used an extra strong solder to firmly attach the cap to the projectile´s nose. he correlated this observation with differences in perfomances established by decapping trials.

The idea that without cap´s a shell wouldn´t function properly is certainly true- in case it hit´s armour aproaching the hardness level of the projectile´s surface where hit- which in the US´s case would require face hardened armour to defeat the nose and stronger than usual, homogenious armour to damage the base.
French homogenious, ductile armour was not hard enough to damage the US projectile, though face hardened armour certainly was. From french reports, it also appears to be clear from the fact of cap´s seperate impact in the hull that cap-seperation of US super heavy projectiles happened. That doesn´t necessarely mean that the projectile suffers much damage as long as it engages homogenious armour.

RobertsonN
Member
Posts: 197
Joined: Wed Jan 05, 2011 9:47 am

Re: Battleship Vittorio Veneto

Post by RobertsonN » Fri Feb 24, 2012 8:52 pm

I just realized that the test results Bagnasco gives make possible a comparison of the performance of the deck armor layouts of US and Italian battleships against AP bombs dropped from a high altitude.

Friedman gives US battleships as safe to 1600 AP bombs below heights of: 8750 ft (North Carolina), 11800 ft (South Dakota) and 12200 ft (Iowa). These are very likely all calculated results.

Bagnasco gives for the Littorio class against a 1760 lb AP bomb, probably for the 100 mm section of the main deck, as 8200 ft (1935 test); and for the 150 mm deck over magazines against an 1800 lb AP bomb, 14100 ft (1943 test).

Taking these figures, the deck over the machinery was comparable in its effectiveness against AP bombs to that of the North Carolina, while the deck over the magazines was better than that of the Iowa. Whether such a large difference was sensible is another matter. However, certain other designs (the British G3, Nelson and final Lion designs) had similar disparities. The final Lion design was for exactly the same thicknesses as Littorio, namely, 4 in over machinery and 6 in over magazines, showing a reduction over earlier designs similar to that discussed for Japanese battleships of the 111 class by Dave Saxton on this site yesterday.

I agree that on the US ships the upper deck was probably a yaw deck as well as a bomb deck because, without this factor reducing the performance of incoming shells, the official immune zones seem rather implausible.

The Italians, on the other hand, looked for performance reduction of shells through decapping. So far, in Bagnasco's book, I have not seen the term yaw used at all.

User avatar
tommy303
Senior Member
Posts: 1528
Joined: Mon Oct 18, 2004 4:19 pm
Location: Arizona
Contact:

Re: Battleship Vittorio Veneto

Post by tommy303 » Fri Feb 24, 2012 11:44 pm

Friedman gives US battleships as safe to 1600 AP bombs below heights of: 8750 ft (North Carolina), 11800 ft (South Dakota) and 12200 ft (Iowa). These are very likely all calculated results.
Not necessarily. Modified obsolete guns ranging from 9.2 to 12 inch (all the way up to a purpose built 36-inch mortar) were used as test weapons for bombs, and presumably defensive systems.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

Post Reply