American SH shells - Famed or Folly

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Billy
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American SH shells - Famed or Folly

Post by Billy » Mon May 01, 2017 10:44 pm

The use of the Very heavy 2700 lb shells have been vaunted over the years. And looking at it it has allot going for it.
1. Resonably good initial velocity - 2500fps ( for the 50 )
and awesome momentum energy values.
2. Excellent velocity retention at range.
3. Excellent deck penetration values at long range.

However what seems to be not immediately apparent is that it had to pay a compromise.

So what Ive found so far is.

Armour belt penetration is not a momentum based calculation but has more to do with velocity.
ie. According to the experts for a 2100 lb shell vs a 2700 lb shell in armour penetration. The 2700 lb'er needs 94% of the velocity of the 2100 lb shell for the same penetration despite the much greater momentum. So therefore for the same charge the lighter shell will have quite a large margin not just in velocity but in penetrion too. So then following this reasoning, the earlier 45 calibre gun firing a lighter 2100 lb shell now at 2600 fps instead of 2300 fps would have just about the same penetration as the the later 50 cal long version. Only its a lighter gun with less recoil and less weight. My own tentative calculations would suggest a 12 % penalty firing the heavier shell in armour penetration values. There is also velocity retention but it has quite a lead up with and by the time it does its already at long range where hits are unlikely compared to the greater advantage of the better penetrations at normal practical battle ranges. That and the lighter shell is a flatter shooter with bigger danger space ( more chance of a hit ) and less time of flight.

Then theres deck penetration. The 2700 lb'er seems to have been designed for long range gunnery with great deck penetration capability. Again at long range and the ranges they anticipated were far beyond that which were actually engaged in in ww2 ( short medium to medium ranges far more common) The longest range hits were Scharnhorsts hit on Glorius at 26000 yards (24km) and there was a similar distance hit from a Brittish ship on an Italian warship. It also seems that at those longer ranges ie 26000 yds the heavier shell didnt carry that much of an advantage anyway ( not at the very ling range where it does carry an edge) and with the included unlikelyness of a hit seems a heavy penalty to pay. It seems night action and close range encounters were the more common in the Pacific.

Then there is also other unforeseen consequences. The 2700 shell was longer so that can also hurt penetration in higher obliquities. Base slap and shell destruction without penetration.

Just seems an actual compromise that is too expensive to pay given its limited or non practical uses.

Byron Angel
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Re: American SH shells - Famed or Folly

Post by Byron Angel » Mon May 08, 2017 10:01 pm

I do agree that the likelihood of hits at 30k+ yds was perhaps less likely under service conditions than suggested by peace-time practices and projections, but some thoughts for consideration -

> Rule of thumb considered that the likelihood of a deck hit versus side hit reached 50/50 at about 15deg angle of fall. This would equate to about 20k+ yds for a 16in gun; at 30k+ yds angle of fall would be about 30deg. This is not to say that a deck penetration into the vitals of a modern first class well protected ship would necessarily be achieved at such ranges. But such a big projectile getting over the vertical protection and into the hull of the target ship would nevertheless produce a great deal of damage above the armor deck and whatever was going on beneath the armor deck had important components that were locate or routed above the armor decks (barbettes, funnel uptakes, intake fans, fire control director circuits, bridge communication circuits, etc).

> A sacrifice in maximum possible vertical penetration performance was certainly made as the price for optimizing deck penetration performance; but vertical armor penetration performance was still quite respectable. Numerous older and/or less well protected (hence more vulnerable) capital ships were afloat then: the old updated battleships and battle-cruisers of the IJN (which represented the principal projected opponent of the USN prior to WW2), French battle-cruisers (Dunkerque Class), German light battleships (Scharnhorst Class).

> The fact that Bismarck's vertical protection scheme was deemed to be technically proof against almost any battleship gun afloat at any range in terms of a projectile piercing and reaching her vitals at short ranges suggests that perhaps USN designers were on the right track. In the event, the performance of the US 2700lb AP projectile versus the horizontal protection of Jean Bart and against general protection schemes of the older Kirishima, Yamashiro and Fuso suggest that the trade-off paid off for the USN in WW2.

Strictly my opinion, of course.

Byron

Thorsten Wahl
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Re: American SH shells - Famed or Folly

Post by Thorsten Wahl » Tue May 09, 2017 11:30 am

both shells wer fired using the same energy at the muzzle (about 300 MJ)

expected result at 24 kyard
Shell ----AOF---- Speed ----flightime --nominal single plate penetration
2240lb---22°---- 1538 fs ---38,8 s ~4,5 Inch deck pen, ~14,5 Inch vertical pen
2700lb---23,8°-- 1533 fs ---41,2 s ~5,5 Inch deck pen, ~15,5 Inch vertical pen

penetration acc ORD 653 armor penetration curves 1942
penetration calculated with US empirical ( Thompson F-Formula) Buord. Sk. 78841
--------------------------------------------------------------------------------------------------------
Comment
F-formula tends to
overestimate required velocity necessary for low obliquity penetration of thick Class A-armor (for 15" US avrg Class A armor required velocity for penetration (NBL) was only about 90% of calculated velocity acc Buord. Sk. 78841 for the light projectile )

and tends to
underestimate required velocity for penetration of relatively thin class B-armor (US avrg armor 110-120% at high obliquity depending on projectiletype and AP-cap and 105-110% at low obliquity against smaller caliber (6"-) weapons.

based on real shots against armorplates.
---------------------------------------------------------------------------------------------------------
some time ago i made a superficial energetical comparison of both projectiles. The lighter projectile probably requires a little bit less energy then the superheavy( about 1-2%) for a given depth at most impact conditions. But the difference appears negligible, with usual differences in projectile- and plate-quality in mind.

At ranges of 24 kyard and above the flighttimes ~40sec became the real problem
at 30 kyard flightimes becomes 53(light)/56(superheavy) seconds.

Any ship not unlikely outmaneuvers the predicted firing solution.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

Thorsten Wahl
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Re: American SH shells - Famed or Folly

Post by Thorsten Wahl » Tue May 09, 2017 3:23 pm

> The fact that Bismarck's vertical protection scheme was deemed to be technically proof against almost any battleship gun afloat at any range in terms of a projectile piercing and reaching her vitals at short ranges suggests that perhaps USN designers were on the right track. In the event, the performance of the US 2700lb AP projectile versus the horizontal protection of Jean Bart and against general protection schemes of the older Kirishima, Yamashiro and Fuso suggest that the trade-off paid off for the USN in WW2.

Strictly my opinion, of course.


Kirishima was defeated at comparatively short distance (non deck compromiting), with it's almost "paper thin" side protection for battleships, sheer size of shells dont played any role. Washington moved the MPI back and forth over the ship especially several underwater hits sealed the sinking.

Fuso was not sunk by american shells but torpedoes
At the same Battle Yamashiro faced 6 US BBs of TG 77.2 armed with -non Superheavy- firing guns and outflanked before by US destroyers and being torpedoed. It received the "finishing HE-Shells", beeing basically blind against radar directed firing of the american BBs at non deck compromiting range.

Jean Bart appears as question mark. With regard to armor quality and presentation of armor to the incoming shell.

Bismarck
Sum of nominal armour plate thicknesses over magazines was 160 mm. This seems comparative to latest US horizontal BB protection with regard to potential fatal hits into a magazine.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

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Alberto Virtuani
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Re: American SH shells - Famed or Folly

Post by Alberto Virtuani » Thu May 11, 2017 12:18 pm

Thorsten Wahl wrote: "Bismarck. Sum of nominal armour plate thicknesses over magazines was 160 mm."
Hi Thorsten,
sorry for my probably stupid question: where have you found this figure ?
I had in mind 50+80 mm (= 130 mm) over machinery and 50+95 mm (=145 mm) over mags. Are you referring to an equivalent thickness, as effect of the decapping weather deck ?

Bye, Alberto
"It takes three years to build a ship; it takes three centuries to build a tradition" (Adm.A.B.Cunningham)

Thorsten Wahl
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Re: American SH shells - Famed or Folly

Post by Thorsten Wahl » Thu May 11, 2017 1:13 pm

I'm sorry - made a typing error
typed 6 instead of 5

magazine protection
150 mm total thickness; 50 mm (whether deck) + 100 mm (armor deck)
from official drawing Amt für Kriegsschiffbau "Schlachtschiff F gültig nur für Panzerdicken"

link (zoomable)
https://photos.google.com/photo/AF1QipO ... fVroHc01_D

preview
Image

effective equivalent thickness, as effect of the decapping weather deck ? possibly in the order of ~ 165 - 180 mm if we take a possible gain number statet in W. Hurlich. "Spaced armor" 1950 "When, however, projectiles are not broken, but only decapped or yawed, weight savings of 10% to 20% can be effected if the projectiles are yawed to impact
the main armor at an increased obliquity."

BUT
"If the projectiles are yawed to impact the main armor at a reduced obliquity, spaced armor becomes considerably less efficient than the same weight of solid armor". I found such sample in a US ballistic tests on tests with 3" projectiles versus model deck protection of american BBs. Unfortunately only one test at only 30 degrees obliquity.

the german horizontal protection offers another peculiarity that neither the descriptions from Hurlich for yaw wich "increase" or "reduce" obliquity were applicable. The british ballistic tests describeed the projectile failure as "topple", the projectile makes a somersault on impact on the main armor plate caused by yaw above the so called optimal yaw wich supports pentration.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

Byron Angel
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Re: American SH shells - Famed or Folly

Post by Byron Angel » Thu May 11, 2017 2:14 pm

Thorsten wrote -
Kirishima was defeated at comparatively short distance (non deck compromiting), with it's almost "paper thin" side protection for battleships, sheer size of shells dont played any role. Washington moved the MPI back and forth over the ship especially several underwater hits sealed the sinking.

> With respect, Thorsten, I feel you missed my point, i.e. - that the sacrifice of a small increment of vertical AP performance in pursuit of optimized horizontal AP performance was justifiable, given the likely (IJN) capital ship opposition to be encountered. As for size of projectile, are you saying that the 2700lb projectile failed to do a satisfactory job?

Fuso was not sunk by american shells but torpedoes
At the same Battle Yamashiro faced 6 US BBs of TG 77.2 armed with -non Superheavy- firing guns and outflanked before by US destroyers and being torpedoed. It received the "finishing HE-Shells", beeing basically blind against radar directed firing of the american BBs at non deck compromiting range.

> Your point about the projectile used by the old US BBs at Surigao Strait is correct, but the point I was seeking to make remains the same: the small sacrifice of vertical AP performance in the design of the 2700lb projectile would not have affected the outcome of a battle in which the older, lighter weight 16in projectile performed quite adequately against the opposition encountered ..... which goes back to my above comment about anticipated opposition

Jean Bart appears as question mark. With regard to armor quality and presentation of armor to the incoming shell.

> I'm not sure what question marks there are about the Jean Bart case. Post-action examination of the hit by a French forensic team ascertained that the net angle of attack was (IIRC) 32-33deg to the deck armor surface. US projectile designers were not responsible for the type of armor steel chosen by French designers. They were only responsible for designing a projectile that would defeat the heavy horizontal protection schemes likely to be found on modern capital ships. One can argue that Jean Bart was only a single case, but, to give credit where credit is due, the projectile completely performed as intended on that occasion.

Bismarck
Sum of nominal armour plate thicknesses over magazines was 160 mm. This seems comparative to latest US horizontal BB protection with regard to potential fatal hits into a magazine.

> I am not certain what relevance this has to my previous post; I do not recall, in any case, having made any claims that the US projectile was able to defeat EVERY possible horizontal protection scheme. With respect to Bismarck's horizontal protection scheme, my recollection is that its principal feature was the distance a projectile would have to travel between fuze initiation and the main armor deck whereby typical fuze delay times would cause a projectile to burst before reaching it. My reference to the Bismarck did not in fact relate to that; it actually related to her well-designed vertical protection scheme (belt + scarp) which, according to my good friend Nathan Okun, was technically able to protect her vitals from any sort of belt hit - the logic being that if it were feasible to provide such a degree of side protection in a modern capital ship, then a design favoring best performance against horizontal armor versus vertical armor made some sense.

Regards / Byron

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Re: American SH shells - Famed or Folly

Post by Thorsten Wahl » Thu May 11, 2017 4:39 pm

then a design favoring best performance against horizontal armor versus vertical armor made some sense.
dont understand me wrong. its not the question of "defeating EVERY possible horizontal protection".

The superheavy shell shrinks the difference between inner and outer limit of vertical and horizontal protection for any combination of given armor weight. This is a comprehensible and rational decision.

its a compromise, ---------------- as usual.

At the cost of 20% more weight compared to an "light weight shell of the same caliber or 50% compared to an 38 cm light weight shell for the same explosive content.

And at the cost of range, the superheavy shell renounced from~10 % range, based on the same energy of propellant charge. On these 10% additional range the same armor is also vulnerable to the lighter shell, (whilst completely save against the superheavy).
If we neglect the hit expectations totally, then the lighter shell allows also for fluke hits with devastating potential at these 10% higher ranges. It doesnt mean it was useful to shoot at this distance. And military command "loves" uncertainty.

The advantage of the SH shell appears in a region of range, where the hit % became inconvinient. In contrast ww2 experience showed decisive shoting results against battleships only at ranges, that where very much lower. With accordingly increased risks.

And battleships represent a considerable value (of the national wealth) of any nation including ~three years of construction of thousands of skilled workers.

Better choose a weapon that can deliver its explosive content from greater range with greater reliability and accuracy ie aircraft. The hit % of their weapons are the same, even the aircraft carrier is 50 or 1000 miles away.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

Byron Angel
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Re: American SH shells - Famed or Folly

Post by Byron Angel » Thu May 11, 2017 11:09 pm

The range of the 2700lb projectile when fired from the 16in/45 @ 2300 fps was somewhat over 36,000 yds. The ballistic performance of the high velocity German 38cm/L52 was indeed superior to the 16in/45 (2700 lbs) up to about 32,000 yds (at which point comparisons become more complicated). IMO, the lesser 36,000 yd range of the 2700lb projectile when fired from the 16in/45 gun was a reasonable compromise between shell weight and reach; 36,000 yds is the furthest distance that a hit by a capital ship main battery upon a moving ship target under action conditions was ever even claimed.

However, when fired from the 16in/50 of the Iowa Class battleships (@ 2500fps), the 2700lb projectile would reach out to about 42,000 yds and ballistic superiority would pass from the 38cm/L52 to the 16in/50 at about 21,000 yds or so.

38cm/L52 15in German gun
16in/50 US gun

21,870 yds - 1,677 fps - 16.4 deg - 32.0 sec
22,000 yds - 1,692 fps - 17.3 deg - 33.3 sec

27,340 yds - 1,552 fps - 23.8 deg -
28,000 yds - 1,587 fps - 25.3 deg - 45.7 sec

32,810 yds - 1,499 fps - 31.9 deg - 55.5 sec
33,000 yds - 1,555 fps - 33.0 deg - 57.8 sec

38,280 yds - 1,516 fps - 40.3 deg - 69.9 sec
38,000 yds - 1,577 fps - 41.6 deg - 72.5 sec


The 16in gun family and its related suite of "super-heavy"projectiles were designed at a time when the threat of carrier aviation was a relatively unknown X factor and at a time when the clear expectation was that Japan would be the likeliest enemy, that any naval war would be fought in the Pacific with its greater degree of average daytime visibility, and that the IJN itself had been busily increasing the reach of its capital ship main batteries through both improved projectile design work and gun elevation increases included in its massive rebuilding program..

As you implied ...... "compromises" are inherent in every design.

FWIW.

Rgds / Byron

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Re: American SH shells - Famed or Folly

Post by Djoser » Thu Aug 31, 2017 11:13 am

Billy wrote:The 2700 lb'er needs 94% of the velocity of the 2100 lb shell for the same penetration despite the much greater momentum. So therefore for the same charge the lighter shell will have quite a large margin not just in velocity but in penetrion too.
F = MV squared

Just as in boxing, speed kills quicker than mass. But beware the heavyweight punch if you are a middleweight.

Good thread, thanks.

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