Bismarck construction flaws

[lwd]

The final straw was the failure of several Mark 21 BDF used in the 16" Mark 8 AP projectiles when firing on the JEAN BART at Casablanca during Operation Torch -- after inspection of the duds (about half of the shells) some of the fuzes were found to have failed due to this corrosion problem

I'll take his word until someone produces some solid evidence to the contrary.

Which shells ?
Mass fired 786 x 16" shells that day.
...

It doesn't really matter does it? The point was that a problem was identified and that that same problem likely exited (depending on when the shells were manufactured) on the Washington as well.

[alecsandros]

It doesn't really matter does it? The point was that a problem was identified and that that same problem likely exited (depending on when the shells were manufactured) on the Washington as well.

Well, it is more complicated than that.
Mass fired quite a lot of shells against battery El Hank, situated inland. If the US forces managed to study unexploded 16" shells, they most surely were found around battery El Hank.
Now, the AP shells in general had the tendency to not explode at all. This is because the way they were designed - to first perforate a given amount of steel, and than to travel some distance, and only after that to explode. [remember the 15" hit on Prince of Wales con tower, or the 14" hit on Bismarck;s forecastle - the shells simply did not find enough armor to fuze - deceleration rate was to slow] So, first the fuze must be initiated, "timer" started, and only after the time delay passed would the filler explode. US 16" AP shells for instance had an average of 0.033seconds fuze delay.

The shells interaction with armor plate was different from the interaction with the ground [as this appears to be the case].

Thus, I don't think any aspects can be inferred to ship-to-ship capabilities, especialy as Massachussets fired very well against several naval targets that day, against which the shells performed exactly as expected.

[lwd]

It doesn't really matter does it? The point was that a problem was identified and that that same problem likely exited (depending on when the shells were manufactured) on the Washington as well.

Well, it is more complicated than that.
Mass fired quite a lot of shells against battery El Hank, situated inland. If the US forces managed to study unexploded 16" shells, they most surely were found around battery El Hank.
Now, the AP shells in general had the tendency to not explode at all. This is because the way they were designed - to first perforate a given amount of steel, and than to travel some distance, and only after that to explode. [remember the 15" hit on Prince of Wales con tower, or the 14" hit on Bismarck;s forecastle - the shells simply did not find enough armor to fuze - deceleration rate was to slow] So, first the fuze must be initiated, "timer" started, and only after the time delay passed would the filler explode. US 16" AP shells for instance had an average of 0.033seconds fuze delay.

The shells interaction with armor plate was different from the interaction with the ground [as this appears to be the case].

Thus, I don't think any aspects can be inferred to ship-to-ship capabilities, especialy as Massachussets fired very well against several naval targets that day, against which the shells performed exactly as expected.

They could also have come from shells fire vs Jean Bart that missed (I think several of the merchant ships sunk in the harbor weren't really the targets but collateral damage from the engagement vs Jean Bart). However that's irrelevant. The corrosion problem that was discovered meant that starting about 6 months after manufacture the fuze had an increasing probability of simply not functioning at all. The imlication is clear that any hit that might otherwise have resulted in a high order detonation could end up with no detonation due to the corrosion problem and that the probabilty of it was dependent on the manufacturing date of the projectile. It has little to do with what the shells are interacting with.

[alecsandros]

The imlication is clear that any hit that might otherwise have resulted in a high order detonation could end up with no detonation due to the corrosion problem and that the probabilty of it was dependent on the manufacturing date of the projectile. It has little to do with what the shells are interacting with.

This has been discussed several times before,
the point is that the projectiles which did hit naval targets during the Naval Battle of Casablanca appear to have functioned just as one would expect AP shells to behave. G%D mention 2 ships sunk in the harbor by 16" shells, 5 hits on Jim Bean and 3 destroyers damaged by Massachussets main guns, one of them badly damaged.

Anyway,
We don't know how many shells did or did not function during Washington's engagement with Kirishima, but the obvious quesiton for me is: if they did not function (explode), and thus became inert missiles traveling at 600m/s, where did they go ?
Where are the exit holes mentioned ?

[lwd]

But we don't know if the shells that sunk the other ships in the harbor or for that matter the ones that damage the destroyers "should" have detonated or even if they did detonate. For that matter were the DDs all hit by main gun fire or was some of the damage inflicted by secondaries? Furthermore if the shell didn't explode because it wasn't expected to it doesn't mean that it would have if it was expected to.

[alecsandros]

For that matter were the DDs all hit by main gun fire or was some of the damage inflicted by secondaries?

According to the reports, only by 16" gunfire.

Furthermore if the shell didn't explode because it wasn't expected to it doesn't mean that it would have if it was expected to.

And it doesn't mean that it wouldn't either.

[tommy303]

On the whole, I would expect most of the 16-inch AP fired from Massachusetts to have functioned more or less within the parameters of the fuze design. The battleships AP was fuzed with Mk21 BDF fuzes. Unlike the German BDZ C/38, the Mk21 was not a graze action type fuze. The USN was almost paranoid in seeking absolute bore safety, and so the fuze did not fully arm until actual impact and needed the deceleration produced by 4-inches of armour plate or an equivalent; graze action fuzes arm fully a very short time down range, and some designs are fully armed before the shell even leaves the muzzle. Taking the BDZ C/38 as an example, a graze action fuze will function or initiate at very oblique angles of impact and initiation will occur against half the thickness of armour or even close spaced multiple layers of structure. The Mk21 was less likely to initiate at more oblique impacts but was probably less likely to suffer enough damage to malfunction at higher velocities and low to normal angles of impact than a typical graze action fuze.

In very general terms, the shelf life of the Mk21 was good when stored in transport containers. The problem of corrosion to the internal parts and sliding surfaces inside the fuze only began when the fuzes were installed in the shells. Shells and fuzes were normally transported separately and only mated when the shells were about to be loaded aboard the ship for which they were destined. It was not fully appreciated at the time, that fumes from the Explosive D shell filler would gradually infiltrate the fuzes and begin to corrode susceptible internal parts and surfaces even though the fuze itself was well protected from outside moisture once installed in a shell. Following a high number of duds early in the war, the problem was eventually diagnosed and subsequent Mods of the Mk21 had Bakelite seals which prevented the Explosive D fumes from penetrating to the interior of the fuze.

In the case of the Massachusetts during the action with Jean Bart, the shells had only been aboard a few months before being committed to the invasion of North Africa, and it is likely that corrosion did not play an important part during the action. Certainly, photographs of surrounding dock areas seem to show cratering in the concrete appropriate to an exploding 16in AP.

[lwd]

Yet we have a report by a well known source that the problem was discovered as a result of examing the rounds fired during that engagement. Indeed the round that hit the turret may well have been the one that identified the problem as I beleive it was the one that ended up in town. Now the shell would not have neceesarily been expected to explode in those circumstances but if the base was relatilfy intact it could have been noted that the fuze did not initiate. This is speculation of course. It is worth noteing that she was commisioned just about 6 months prior to the engagement if the rounds were uploaded at that time there was just enough time for this problem to start surfacing. Washington on the other hand was commissioned ~18 months prior to her engagement with Kiroshima. Which suggest that the corrosion problems could have been significantly worse.

[alecsandros]

Of course,
this is just speculation.

Again, IF Washington's fuzes did not work, where did the 600m/s 16" shells go ?

[lwd]

Of course,
this is just speculation.

The possiblity as to what shells it was that clued them in is indeed speculation. I've seen nothing to refute the fact that the problem was discovered after and as a result of Mass. shooting during Tourch. Which woul hardly have allowed for any corrective action to be taken before Washington engaged Kirishima.

Again, IF Washington's fuzes did not work, where did the 600m/s 16" shells go ?

??? Where do you thinkthey would have gone? Of course I'm not saying all the fuzes didn't work or even that any didn't work just that it was a possiblity. If they didn't detonate most would almost assuredly end up in the ocean. Some might still be inside Kirishima depending on what they hit others might be resting on one of the nearby islands (examing the track charts might tell if this was possible). One of the points of course is that non detonating hits would be pretty hard to spot at night. It might also support the underwater hits as it would explain why they didn't detonate before they reached Kiroshima's hull, which I think would be expected at those ranges would it not?

[alecsandros]

which I think would be expected at those ranges would it not?

The non-detonating shells would travel to fast to be stopped by anything Kriishima had on board. This would mean double holes for most trajectories (through-and-throgu), thus the ship being holed twice by many shells.
HOwever, there is no mention of this on Lundren's paper, which makes me wonder...

[tommy303]

LWD is correct. I did a little more digging, and apparently half the 16inch hits on Jean Bart were duds, and several of them were directly attributed to corroison by the ammonia fumes given off by the Explosive D. The diagnosis was easy with several shells on hand to examine, although the solution of using liquid bakelite took until mid-1943 to implement.

[alecsandros]

LWD is correct. I did a little more digging, and apparently half the 16inch hits on Jean Bart were duds, and several of them were directly attributed to corroison by the ammonia fumes given off by the Explosive D. The diagnosis was easy with several shells on hand to examine, although the solution of using liquid bakelite took until mid-1943 to implement.

I don't understand how this was concluded.
There were 5 hits on JB: 2 penetrations followed by explosions, 2 shells broken up in contact with heavy armor and 1 indetermined.

The "analysis" probably concerns the 2 shells that broke up in contact with turret and barbette armor. However, it is very slippery to conclude that those 2 shells wouldn't have functioned properly provided they would have perforated the armor.

ALso, 2 shells is a pretty damn small statistical selection.

[lwd]

...The "analysis" probably concerns the 2 shells that broke up in contact with turret and barbette armor. However, it is very slippery to conclude that those 2 shells wouldn't have functioned properly provided they would have perforated the armor.

Not at all. If the fuze did not initiate vs the turret or barbette why would it have initiated vs lesser armor?

ALso, 2 shells is a pretty damn small statistical selection.

Yes and no. If you find a problem in 2 out of 2 or 3 or even 2 out of 5 it's pretty clear that a problem exists. What's not clear is how significant the problem is. In this case though they could check the fuzes on rounds stll in the magazines and correlate it with data on when the rounds were assembled. The rounds fired at Torch didn't define the problem by any means but they gave a clue that it existed.

[alecsandros]

Not at all. If the fuze did not initiate vs the turret or barbette why would it have initiated vs lesser armor?

Because the shell was broken up by the impact and the compounded obliquity was quite high.

It all depends on the exact forces acting upon the shell (and most importantly upon the back side of the shell) on the moment of impact. If those forces allow the base of the shell to be relatively undamaged during the initial fases of the impact, the fuze may be activated; if not, and the intitial phases include base slap, or any other damage producing phenomenon on the back of the shell, the fuze may not work at all.

It was common knowledge in all major navies that non-penetrating AP hits were most likely to become inert. Everyone knew about it, but soluitions were very hard to come by.

It was called "fuze blindness" IIRC.