German Battleships and convoy hunting.

[delcyros]

From what is visible on the wreckage, the belt was penetrated by 16" and 14" hits (all deflected, so there were no vitals hit), and at least one torpedo hit the catapult deck

[DerAdlerIstGelandet]

Yes I agree syscom but it did not happen that way...

[syscom3]

This was for a hypothetical encounter of the Bismark and torpedo bombers from an escort carrier.

[DerAdlerIstGelandet]

Okay agreed then.

[delcyros]

Even if you place the torpedo hit´s exactly, at least 14 hit´s are needed to sink a Bismarck class BB (minimum according to compartimentation (including all weaks) and floating reserve), around 20 would be more reasonable. That´s really a lot. If we take into account that around 80 (out of 300+planes total) torpedo bomber got 12 hits on bigger sized Yamato´s and Musashis (bigger ok, but they were more maneuverable than the Bismarck´s also) you will need around 100-120 torpedo bombers to sink a Bismarck class ship with CVE-means only. How many torpedo bombers carried a single CVE? Usually 0. How many planes would carry in case they had torpedo´s? Between 6 (Audacity) and 30 (Sangamon) planes total, that are around 3-12 torpedo planes per CVE, so you would need to accompany some 10 Sangamon class escort carriers for a decisive blow (just mathematicly, but this is nonsense, I know). That´s more than was avaiable for a single convoi (or even five), it´s almost it´s own fleet, or isn´t it?
And three-ten planes performing their run alone would be good food for AA (in case they are fast enough to be tracked by firecontroll), if a CVE decides to atack wave by wave.
No, I don´t think it is a reasonable scenario. CVE would be good to report a raider, but they are too slow (rarely made 15 kts.) to track them for a prolonged period and they hadn´t the logistic background to do concentrated attacks on their own.

[syscom3]

Look at it this way, suppose using the numbers from the Yamato were applied to the Bismark from a single CVE carrying 12 torpedo bombers.

One out of every three torpedo's launched could be expected to hit. Just for this scenario, say only two would hit. Now consider that after attack the planes return back to the CVE for another reload and go back. It wont take time at all for a quite a few torpedo's to have hit it. The same situation happened between the USN and IJN fleet action in the battle of the San Bernardino Straight (in the PI, 1944).

One thing that was proven in the PTO was AAA from the fleets couldnt stop all of the attackers. More than enough got through. Considering that the Bismark would not be operating in a large sized task force with its massed number of guns, I would say not many attackers would be shot down.

Plus, once the Bismark was under torpedo attack, it would have to go into evasive maneuvers which meant it would not be getting closer to the convoy it was hunting. Every hour it was under attack and maneuvering meant other RN and USN forces (air, sea and air) would be getting closer to it.

[delcyros]

I got your argument.

WW2 records show that the hit percentage compared to started planes was well below 5% as long as the ship is maneuvering. And with 12 torpedo bombers You could expect something between 0.6 and 1.2 hits, that´s not much (esspeccially since the raiders are quite immune) but it might effects the ships range or (to a lower degree) speed. Keep in mind that between 10 and 30% of the air relaised torpedos will fail to detonate properly. Twelve bombers are a good number to deal with by AA fire. I don´t expect that a number of them will be shot down (since US and british planes can sustain much more battledamage than their japanese counterparts) but it will be hard to get a clean shot anyhow. Those twenty torpedo bombers attacking Tirpitz got not a single hit, while none of them was shot down (5 severly damaged), post battle reports showed that AA fire was very effective, so they had to release the torps from longer distance or unfavourable angles. Unless the bravery of the pilots is extraordinary or the will to do suicide (the closer they get on the BB the better the chances to hit and the more effective is AA), which would result in both, more hits and higher loss rates, I see no sense in this tactic from the RN/US point of view (which generally was careful).
A first line Carrier (just like those to attack Musashi&Yamato) would have a better chance to perform effective torpedo runs due to the higher number of planes involved (fighters going to starfe the BB´s AA, Bombers attacking the ship from above while in the same time torpedo planes perform attacks from the sides).
Another concern with CVE is their very limited worth at Beufort 5 or higher. At stage 6 only rarely sortieswere flown. And since the raider always seek bad weather circumstances (ok-planes do have a longer range) and factoring the north Atlantic weather there would be a narrow window for any CVE operations. And those CVE would be very exposed to the raiders once they get contact (which would happen in case they are ordered to stay in convoi formation sooner or later).
However delaying the ship, knowing it´s position and a good deal of teamwork between task forces and CVE will hunt the raiders effectively, hands down.

[trackend]

The Bismark was undoubtedly a tough nut to crack and the Homogeneous Armour steel was very robust however it is forgotten that many torpedoes not only used contact exploders but as in the case of the 18inch British Mks carried by the String bags they used the duplex pistol which enabled either contact or proximity detonation this enabled deep setting and there by attacking the weaker parts of vessels namely the keel plates that where much thinner than the well protected sides.
This type of detonation was attempted to be countered by the fitting of degaussing equipment (Magnetischer Eigenschutz) but was limited in effect by the torpedoes only passing within a few feet of the ship as opposed to the considerable distance that magnetic mines operated from sitting on the sea bed as they did.
The best defence that the Bismark had against this type of explosion was as with most navel vessels , multi compartmentation this meant that it would take numerous hits in various areas in order to flood sufficient compartments to cause the ship to founder. I believe the Bismark had in the order of 200 compartments in each of her 4 decks. So even that method of attack was not easy but as was the case in reality although the ship remained afloat, as a fighting unit it had no ability to continue to fight after everything from stem to stern had been raked by enemy shell fire and the gunnery control systems had been destroyed.

[delcyros]

Yes.
I don´t know how well either magnetic pistols or MES were working, but I suspect that both had disappointing reliabilty prior to 1943 (referring to the replace of magnetic pistols from Victorious and Ark Royal in 1941 as well as the three mine hits at Gneisenau and Schanrhorst during their channel operation[I suspect this were magnetic ones but I don´t know]).
The degree of total compartimentation of Bismarcks hull (including the hulls decks above the normal waterline) is stated with 800, but this figure only tells us how many "spacial units" were there. A torpedo hit usually will cause several "units" to be flooded, so it´s better to take on the main compartimentation (divided by each other with armor grade plates of at least 45 mm thickness), so they are really tough nuts to crack). We do have 23 of those, called Abteilungen, in case of Bismarck (of course each is divided into watertight rooms and sometimes even those are watertight subdivided, too).
The only warship to carry effective bottomprotection was the Yamato-class with it´s 50-80 mm armored hull bottom (which also had enough void cells to contain blast effects). However it wasn´t fully protected, the protection leaves the engine and turbine room blanc, only the main magazines are protected (rarely 20% of the hittable hullsize). While the ship had the highest subdivision known (1174 watertight spacial units, ignoring the void and fuel cells) for any warship, it´s protection was very biased:
The main armor zone covered most of its units (1005) leaving some very large spacial units without any protection in the bow and stern, this is even more worrisome if we factor that almost 35% of the substructure is unprotected by any substantial TDS.

[DerAdlerIstGelandet]

Originally Posted by trackend

The Bismark was undoubtedly a tough nut to crack and the Homogeneous Armour steel

You can go to Kiel, Germany and see one of the Steel Plates from the Bismarck that was just left sitting on the docks after not being used on the ship.

[trackend]

Thanks for the post Del I noted that you said the bow and stern where not as robust as the the rest of the Bismark I'm sure this must have been the reason for the stern breaking off when it hit the sea bed as described by Dr Bob Ballard when he located the wreak-site.

I would be interested to visit Kiel Adler Ive only been to Germany twice once on business too Koblenz and once to see the Rhine in flames festival.
I took this shot of a piece of Tirpitz'es belt Armour at Duxford museum last year.

[delcyros]

Yes, I saw it once (am sure it was KCnew). But we don´t know why it is there. Most certainly because the plate was rejected for use on Bismarck (it carries testmarkings).
This is a problem for so many heavy armor plates: One example; For Littorio we extrapolate it´s armor strength from a very single armor plate specimen (which may be rejected for use as well). According to the understanding of armor in Italy (which was the best in prewar times) it is kind of a surprise that this armor has only slightly better quality than japanese ones. But again, it may be wrong to extrapolate from a single plate of unknown source...

[delcyros]

It really looks like the stern structure was cut of when it hit the sea bed (at around 27-31 kts), agreed. Bow and stern were more fragile but still very tough if we compare them (Iowa, Yamato, North Carolina, South Dakota, the britisch BC and all french BB had no armor enforcement there, Bismarck and Scharnhorsts had 50- mm Wh, but this is still insufficiant to protect from shells or torpedos. The Gneisenau refit should get 80 mm Wh thick bowbelt (which may protect from 6" at long to medium distances). The structure in the bow was much enforced but the stern was weak (Ballard correctly quotes on the stern cut of Prinz Eugen when it was torpedoed there), particularly if we compare this with contemporary designs (the flask like shape of US and Yamato BB turns the stern into a structural very strong but unprotected unit).

[DerAdlerIstGelandet]

Wow nice pic of there from the Tirpitz, preetty amazing actually!

[delcyros]

I just have finished some conceptional studys on Hipper class CA. I always found it strange that they decided to produce 6 of them (Hipper, Blucher, Prinz Eugen, Seydlitz, Lutzow (the later two not finished) instead of some more pocket battleships (Spee, Scheer, Lutzow).
The Hipper class is a lot larger than a pocket battleship but still inferior to ALL major aspects except for max speed:
displacement:

Graf Spee: 16.000 t
Prinz Eugen: 18.400 t.

speed:

Graf Spee: 28,5 kts
Prinz Eugen: 33,5 kts

endurance:

Graf Spee: 17.460 nautic miles / 17 kts (13.500 sm at 20 kts)
Prinz Eugen: 7.200 nautic miles / 20 kts (~ 9.800 sm at 17 kts)

main artillery:
Graf Spee:6 x 11"/52
Prinz Eugen:8 x 8"/60

secondary artillery:
Graf Spee: 8 x 5.9"/55
Prinz Eugen: none

dual purpose:
Graf Spee: 6 x 4.1"/65
Prinz Eugen: 12 x 4.1"/65

torpedos:
Graf Spee: 6 x G7a
Prinz Eugen:12 x G7a

float planes:
Graf Spee: 2 Ar 196
Prinz Eugen: 3 Ar 196

TDS(main torpedo bulkhead):
Graf Spee: 45 mm
Prinz Eugen: 20 mm Ww

belt armor:
Graf Spee: 80 mm (inclined)
Prinz Eugen: 70 mm Wh (80 mm at the magazines)

deck armor:
Graf Spee: 25 mm (45 mm over the magazines)
Prinz Eugen: 12 mm Wh (50 mm over the magazines)

front turret armor:
Graf Spee: 140 mm KC/NC (non cementated)
Prinz Eugen: 105 mm Wh

conning tower:
Graf Spee: 150 mm
Prinz Eugen: 70-105 mm Wh

So at all the ten years older Graf Spee is lighter, better protected, has a longer range and more punch than the new Prinz for a speed loss of 5 kts.
Eventually the Hipper class CA were intended to be CL with 12 5.9" (four triple turrets). The armor scheme fits better with a CL than a CA (esspeccially for its size) if you ask me. With the advantages avaiable in 1938 they should have spared the ressources for the Hipper class in order to lay down four more pocket battleships. At the same displacement (18.400 t.), the ship could still carry six 11" /55 (C34 instead of C28 design, higher elevation and therefor a decent range (42.000 yrds) and punch+ very high cyclic firing rate (17,3 sec. for each gun but usually 19-21 sec. due to triple gun turret design), the removal of 5.9" would allow weight to install 14-18 4.1"/60 dual purpose. Improvements in the engine dep. would make it possible to (nearly) double the poweroutput of the Diesels, so at least 80.000-100.000 SHP are possible (this amount of power is still distributable to the two screw design). An 18.400 t. ship could still make 31 kts and keep its superior range. There are even 800 t. for additional deck armor left (thus approx. 50 mm or 35 mm + 80 mm over magazines)! What do you think?