Belt Armour - what is it good for !

[xj900uk]

I seem to recall they scored several direct hits with their Tallboys over the course of at least two raids (+ a few others where they couldn't find the target).  On the first successful raid,  the Tirpitz coped a Tallboy on the 'foredeck which actually caused irrepairable damage (at least for the facilities available in Norway).  So the Germans came up with the idea of semi-sinking it near a harbour entrance (can't remember which one) and use it as a block-ship/gun battery to protect the defences.

[Panther Bait]

I think the first Tallboy hit in the bow (Operation Paravane) passed all the way through the ship before exploding.  Did a lot of damage but didn't sink the Tirpitz.  The second (successful) Tallboy raid got 2 direct hits on the port side and a few near misses.  The Tirpitz rolled over to port and capsized in shallow water almost immediately.  About 1000 of the 1700 on board at the time were killed (most probably drowned).

[JohnDillworth]

gratuitous picture of torpedo bulges:

[wwengr]

ORIGINAL: JohnDillworth

gratuitous picture of torpedo bulges:

Now I understand! I'll explain to my girlfriend that I have a torpedo bulge. (Around the waist! What were you thinking!) It's a cooler name than spare tire or love handle.

[jackyo123]

ORIGINAL: JohnDillworth

Japanese shells, at least the 8"" ones had a blunter nose than Allied ones. It was found that they traveled underwater a bit better that way. I don't know if it ever came into play in actual combat, but someone was thinking about it. It seem BB's can take 1 or 2 torpedoes and get away but most other ships are in big trouble. I don't know if that is a product of armor or sheer tonnage.

According to a note in Frank's 'Guadalcanal', there is only 1 recorded instance of a Jap 'underwater' projectile working as designed during the war - and that was, IIRC, during the 3rd naval battle around Guadalcanal. Going from memory, I think Kirishima was the ship firing it.

According to the same note, again from memory, the Japanese had found pre-war that projectiles that hit a ship below the waterline did far more damage, so they changed the ballistic properties of their shells to not deform or explode when hitting the water, and that could maintain strength when traveling through ten feet or more of water and striking the target deep below the waterline.

[xj900uk]

Anti-torpedo bilges played havoc with a battle-wagons streamlining, speed and fuel consumption.  No wonder most of the 'spare tyre BB's' couldn't do much above 20 knots,  which is why one certain US Admiral described them as 'too damn slow' to keep up with his carriers...

[Iridium]

ORIGINAL: xj900uk

Anti-torpedo bilges played havoc with a battle-wagons streamlining, speed and fuel consumption.  No wonder most of the 'spare tyre BB's' couldn't do much above 20 knots,  which is why one certain US Admiral described them as 'too damn slow' to keep up with his carriers...

The particular BB pictured earlier could reach 26.7 Kts during trials. More realistic operational speed marks the vessel at 25kts.

[Tiornu]

The blunt cap head of Japanese shell design made it much more likely that the shell would maintain a stable trajectory underwater. This does not mean it made a stable trajectory a probable result, just more likely. The shell that submarined into Boise went under her lower belt. (In that section of the hull, there was no "belt" in the usual sense of an armored waterline--just a totally submerged strake of homogenous armor. US cruiser armor was weird.) I believe three other 8in shells struck Boise's armor in that battle. One hit the thick faceplate armor, left a blunt-nosed imprint there, and accomplished nothing apart from some dramatic splinter damage to the superstructure. Another hit the 5in belt armor, dented it, and caused minimal splinter damage. The third hit the barbette armor, distorting it enough to jam the turret, but broke up in the process; it fizzled rather than exploded. Japanese 8in shells were terrible against face-hardened armor. I think it was Kinugasa that scored these hits.
Other ships were hit below the waterline by Japanese shells, but it's unclear whether these were true submarining shells or simply shells that happened to hit the hull before starting to pinwheel through the water.

[Tiornu]

Three battleship designs had the main belt armor integral with the torpedo protection--Yamato, SoDak, and Iowa. In none of these cases is the armor considered to have been a boon to the torpedo protection. In Yamato's case, there were problems with the joint between the upper face-hardened armor and the homogenous lower belt, while the American ships had their issues at the base of the lower belt. Other battleships had significant armor applied to torpedo bulkheads but not contiguous with the main belt. NC is chief in this category. The torpedo that hit her exploded abreast the armored inner bulkhead; seams were opened, but the extent of flooding was remarkably small, only about 1000 tons including counter-flooding. The main belt did suffer some damage directly above the detonation, and it's been said that she retains the cracked plate to this day. The Montana design also had an armored inner bulkhead, and unless I'm mistaken, all the modernized Japanese battleships had armor added to a torpedo bulkhead. Note that many IJN heavy cruisers also had belts continuing all the way to the bottom through the TDS, but a cruiser's TDS is about as useful as a lizard's bra.
The bulges added during a battleship's modernization are ostensibly a form of torpedo protection, but their primary purpose is to keep the ship afloat after someone slapped 1500 tons of deck armor onto it. The bulge does good service in placing the torpedo's detonation farther away from the centerline, but it also creates the opportunity for some extreme off-center flooding. That would fall into the non-good category.

[John Lansford]

That's why counterflooding was considered a standard tactic after a torpedo hit.  IIRC those bulges also were filled with water or other fluid to provide additional absorbing capability to a warhead's detonation.

BTW, the North Carolina isn't a SoDak design.  It's an earlier class and not as well protected as the SoDak's.

[Tiornu]

The fundamental structure of NC's TDS was considered superior to SoDak's, if only because it was deeper. Designers actually reduced the TDS depth when working on SoDak in the belief that the mass of armor in it would compensate, which appears to have been overly optimistic. The details of Iowa's TDS made it better than SoDak's, but Montana reveals what designers really wanted to do if unfettered by treaty restrictions. Montana looks much more like NC in her TDS. But there was one disadvantage for NC; she was not as flexible in her liquid-loading options as later classes. Though the decision was not unanimous, the USN would switch its stated preference from sandwiching liquid loads between inner and outer voids, adopting instead the use of liquid loads in outer spaces and voids on the inner side. The intent was to limit initial listing after torpedo hits.