Bismarck vs. Iowa

[RobertsonN]

Regarding the poorer results at oblique impact for shells having small cavities (and therefore charges), the only reason I can think of for this is that a smaller cavity moved the centre of gravity of the shell further back, which meant that the transverse moment on the shell during the initial turn away from the normal was even larger, which made breakup more likely. The original reason for the light 16 in Mark I British shell was that it was more likely to remain intact on oblique impact.
Regarding Nowaki, a piece on Avalanche Press referred to elsewhere on this site says the Iowa shot better than NJ, and attributed this to Iowa's guns being warmed up whereas NJ's were not. This lower accuracy during the warmup phase was thought to be caused by the (relative) lightweight construction of the 16/50. It was a powerful gun for its weight.
How accurate were official range tables and flight times? For example, Avalanche says the Iowas tended to overshoot especially at long ranges because, among other factors, the barrel wear was lower (i.e. better) than estimated. Of course, the Americans had more experience of firing at extreme ranges and were therefore more aware of problems than others.
Regarding Bismarck, the MV given is always 2690 ft/s. I take it this was the new gun figure. Does anyone know what the average MV was?

[Bgile]

The US Super Heavy 16" shells did not have poor results at oblique impact.

[RobertsonN]

Perhaps the American shells were superior metallurgically to British ones, so that their 'standard' condition was equivalent to 'custom' British ones.
Gercke gives some discussion of such matters. The shell is hardest at the front and becomes progressively softer and more elastic going back (and therefore resists transverse forces better). The Germans also found that they needed to restrict the hardness of the front of the shell somewhat to ensure intact penetration with a still functioning fuze.

[Dave Saxton]

The difference in weight isn't going to make much difference vs cemented armour as the more important factor is velocity.

dave do you have a source?
Seems to me the formula used for Unterlagen zur Bestimmung Hauptkampfentfernung was using the energy aproach.

Hi Thorsten,

Hoyer mentions that it boils down mainly to striking velocity in practice -among shells of similar caliber. Also Nathan Okun has presented some ideas on this issue in agreement with Hoyer. Nathan's theory is it's because of the greater stiffness of cemented armour.

[Tiornu]

Regarding Nowaki, a piece on Avalanche Press referred to elsewhere on this site says the Iowa shot better than NJ, and attributed this to Iowa's guns being warmed up whereas NJ's were not. This lower accuracy during the warmup phase was thought to be caused by the (relative) lightweight construction of the 16/50.

I would be interested in the source for this. NJ fired seven salvos and scored "several" straddles. Considering these were all two- and three-gun salvos, the gunnery must have been pretty good.
Vanguard's gun range was 33,550 yards, with a maximum of 37,870 yards with super-charges (about a thousand yards short of Bismarck's max).

[lwd]

I think the details of this have been given on this site somewhere. Found at least part of it at: viewtopic.php?f=1&t=1145&p=34788&hilit= ... sey#p34788
Here it is:

The Nowaki gunnery reports for Iowa's and New Jersey's are summarized, salvo by salvo, complete with spotting corrections observed and applied, in Part II of the Fischer-Jurens paper. Anyone who wants to can extract the number of probable straddles, and the number of guns in each straddling pattern, from there. In general it appears that New Jersey straddled twice firing seven two and three-gun cold-gun salvos at about 32000 yards. Iowa straddled on her first eight-gun hot-gun salvo at a range of about 36000 yards, thereafter drifting off target as Nowaki began to maneuver evasively. There may have been other straddles for Iowa as well, as the range corrections for salvos 2 and 3 (of 5 in total) were less than 200 yards, i.e. only about 1/3 of the expected range pattern. These two salvos were also off about 100 yards in deflection -- to be expected, considering what Nowaki was doing. Were Nowaki actually an enemy battleship -- a much larger and less-manueverable target -- it is likely that at least one or two of the first 24 rounds fired would have been hits.

Dispersions would not normally be mentioned in the report of a combat shoot unless they were for some reason seen to be unusual. The gunnery report typically tracks only the correction required to bring the mean point of impact on to the target. Unless commentary is made to the contrary, it may safely be assumed that the observed variations in pattern size and shape, etc., were seen to be unremarkable.

Bill Jurens

Some additional details are also at:
viewtopic.php?f=36&t=2637&p=27014&hilit ... sey#p27014
But looking up the article mentioned above is probably the best bet.

[Thorsten Wahl]

The Germans also found that they needed to restrict the hardness of the front of the shell somewhat to ensure intact penetration with a still functioning fuze.

not only the germans
british research on optimal hardness of cap/projectile brought conflicting requirements regarding hardness at low and high obliquity impact. High hardness lowers ballistic limit at low obliquity <30° but failed (more shatter and higher ballistic limit) at high oblique impacts at around 60°

Regarding Bismarck, the MV given is always 2690 ft/s. I take it this was the new gun figure. Does anyone know what the average MV was?

According Krupp Datasheets for the SK 38 C34(e) gun - WA52-444 und WA52-453(e) life expectancy for the barrel was 242 shoots.
but rapid firing will more rapidly decrease this value. Limit velocity loss for worn barrels was a 10% drop in Vo.

the drop in velocity was not linear (used barrels wore out faster) even the barrel was not chrome plated.

[lwd]

... the drop in velocity was not linear (used barrels wore out faster) even the barrel was not chrome plated.

I would have thought just the opposite in the absence of plating. I'd think there would be less friction due to the wear. Differential hardening maybe?

[RobertsonN]

Thanks for info on wear of German 15 guns: none of the sources I have contain anything at all on wear. A 10% drop in MV corresponds to a lower limit of about 2420 ft/s, so that average MV might have been quite close to the average figure of 2575 ft/s for the British 15 in gun when supercharged. I am a little surprised that the Germans produced lots of data and the well known range, angle of fall, flight time, danger angle, dispersion curves for new gun MVs, because these all somewhat overestimated the danger they posed to the enemy, who would always face guns that had fired a fair number of shells.
Does the comment that wear "might be more with rapid firing" mean that wear might have been more difficult to gauge when the guns were used intensively? The Bismarck had fired her guns a lot against various targets, especially destroyers on the night of 26/27 May. Might a false estimate of what the wear was have significantly added to the problems she had with finding the range against Rodney/KGV? Underestimating wear would lead to a tendency to shoot short of the target.

[Bgile]

My impression of that last engagement is that Bismarck shot better than the British until she lost her main spotting position in the foretop. She also seems to have shot well against KGV with the secondary position until it was destroyed.

[Tiornu]

Did Bismarck fire any 38cm shells at the destroyers? Her 15cm battery was having a difficult enough time trying to stay on target as the ship slewed back and forth.
Bismarck was certainly shooting better than Rodney...until she wasn't.

[RobertsonN]

With regard to destroyers, one was struck by a large splinter which was called the "Bismarck herring".
It was believed to be an 8 in shell that destroyed the Bismarck's primary fire control.
The RN in their development of the Vanguard design to incorporate war experience added a considerable amount of splinter protection to bridges, directors, director communications with the citadel etc. because damage to control positions and directors had significantly degraded the fighting capabilities of both POW and Bismarck. The protection of Vanguard still lacked the heavily armored CT and communications tubes of most foreign ships though. Furthermore, the protection given to the main fire control director position of Vanguard would not have sufficed against an 8 in shell. Perhaps such protection was ruled out on stability grounds that high up.
At the same time, the RN intended to reintroduce the common shell to increase the likelihood of such "non-vital" but still incapacitating damage (South Dakota was another example). By the end of the War (ADM 481 Suppl. 6), they also believed the common shell was capable of great underwater travel (120 ft) to score damaging hits under the belt (like, but probably independently of, the Japanese and inspired more likely by such hits on both POW and Bismarck). The APC was not thought suitable for this role. As a result of the Bismarck actions, it also appears that the RN had abandoned its earlier position (post-Baden trials) that it was possible to sink an opponent with a 100% APC outfit.

[Bgile]

It's not clear to me how one can expect a shell with a .025 fuze delay to travel 120 feet under water.

[Thorsten Wahl]

Thanks for info on wear of German 15 guns: none of the sources I have contain anything at all on wear. A 10% drop in MV corresponds to a lower limit of about 2420 ft/s, so that average MV might have been quite close to the average figure of 2575 ft/s for the British 15 in gun when supercharged. I am a little surprised that the Germans produced lots of data and the well known range, angle of fall, flight time, danger angle, dispersion curves for new gun MVs, because these all somewhat overestimated the danger they posed to the enemy, who would always face guns that had fired a fair number of shells.
Does the comment that wear "might be more with rapid firing" mean that wear might have been more difficult to gauge when the guns were used intensively? The Bismarck had fired her guns a lot against various targets, especially destroyers on the night of 26/27 May. Might a false estimate of what the wear was have significantly added to the problems she had with finding the range against Rodney/KGV? Underestimating wear would lead to a tendency to shoot short of the target.

As far as I know the SK 38 was equipped with a Vo measuring apparatus, so it was possible to determine the Vo loss by wear and fed the data direct into the firing computer without using wear tables. Additional the wear corresponds with an increase of the point where the projectiles were rammed(Ansetzpunkt). When this point was shifted into the barrel by ~50 cm the gun was worn.

any wear will result in a systematic error wich is easy to correct like more dense air.

SUPP 6 /481 "underwater performance of shell" was a technical report on designin shells with stable underwatertravel performance.

[Thorsten Wahl]

SUPP 6 /481 is also the first british ballistic report wich mentions a horizontal protection of 6 inch for Bismarck-Class.

Seems there were some additional findings in between 1942 CB 04039 Addendum 2 Ballistic protection (of british and german Battleships) and 1945 that led british experts to recalculate the horiozontal protection, wich was estimated in CB.... with only 3.2 " neglectin the impact on projectile performance of the 1.9 " whether deck.