1930's Japanese Navy - What would you have done differently?

To add to what I had just said, I was having a similar discussion on a naval forum. Got a reply from someone somewhat familiar with WW2 era fire control. It looks as though the director was indeed used - but the "spotting" might have been done once every 3-5 salvos in a situation like this, the salvos fired between intervals are all based on the most recent update.

is generally referred to as the problem of 'spot pyramiding' (often leading to over correction during rapid fire). This happens when the interval between shots or salvos is less than the time of flight plus the spotting interval, meaning that when a salvo lands there's already another one (or more) in the air. In such situations the spotting will undoubtedly become muddled. The only way to prevent confusion is for the spotter to stop reporting each and every fall of shot, and only do so when he's asked to do it. What happens is that the guys in the plot press a button on the rangekeeper (the main fire control computer) and then after a calculated interval that makes allowence for time in flight, a buzzer will sound, alerting the spotter that a salvo is about to land that needs to be reported on.

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I don't know exactly what the spotting interval would be, but it would require data fed to the director, this being relayed to the plotting room, the firing solution being calculated, relayed the the individual turrets and corrected.

I't think with a 5" gun at 5000 feet this would be a good 15 seconds, 8 for the flight of the salvo and 7 to accomplish all the fire control steps listed above. Actually, 7 seconds seems little time to accomplish all the above, but I am not sure.

If this is correct, with a firing rate of 20 per minute, we have 5 salvos fired for every one correction.

Perhaps this has a lot to do with the lesser accuracy of smaller guns (smaller compared to a cruiser or battleship weapon).

different distances might require different solutions/techniques.

Some Navy's, when firing long distance with battleships/cruisers where the time of flight exceeded the rate of fire, adopted spit salvos. 1/2 the guns firing and then the other 1/2 to keep the time gap between salvos landing down. This did depend on turret layout/design as some turrets didn't allow independent loading or elevation.

A number of Navies got it wrong in emphasizing long range gun fire from destroyers during the 1930s as the very same guns, mounted on cruiser or battleship hulls had longer practical battle ranges. Especially the worse the weather got. The guns had higher command (and were dryer), the gun directors/fire control was higher up giving better visual range and the steadier hulls provided both a better firing platform and higher rate of fire in rough weather. The guns favored by many navies during the 20s and 30s for destroyers could easily out-range their fire control equipment.

Thanks for sharing the stuff, parsifal.

So in summery 4768 German shells from 5-15" guns registered about 47 hits or about 101:1. Breaking this down further we see 34 hits from BB/CA primary batteries shooting 1398 shells or 41:1 rate, and the smaller guns got 13 hits on 3370 shells expended or 259:1. So enough info to suggest that the bigger guns generally do much better.

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Here we have a situation were hits by the main armament were definitely more accurate even when both had the same firing platform. Something above and beyond the firing platform caused this disprepancy. The German 5" Guns (actually a 5.9" weapon) had a rate of fire of 6-8 rounds per minute, the main armament 2-3 rounds.

Just as a side note - The Germans did not use dual purpose weapons for the most part. The 5.9" weapon were excellent surface to surface but useless as AA. They had 12 of the 5.9" weapons, and for AA 16 x 105mm, and 28 20mm-37mm barrels. Probably would have served the Bismarck better to have true dual purpose weapons, possibly could have prevented the torpedo strike that ultimately led to her demise. Still for her time though (1941) she had a pretty impressive array of AA weapons.

I understand though why the Bismarck had her 5.9" secondaries, and the Yamato had her 6.1" weapons. These were relatively high rate of fire and fast traverse for surface combat, but outgunned the standard 5". The biggest interwar fear seemed to be having your capital ships sunk by smaller faster vessels using torpedoes, be it destroyers or torpedo boats. And these mid-size weapon were excellent for that purpose.

OK, a bit off track, largely due to me!

The year is 1930. From a carrier standpoint you have the Hosho, Akagi, Kaga, Ryuho is in progress, the Hiryu/Soryu are maybe on the drawing board, the Shokaku class are probably not that far along.

Battleships - You have the 4 old battleships from the Fuso and Ise Classes, the 2 Nagato class, and the venerable 4 of the Kongo class. The Kongo class had had it's first modernization, other than that no modernization of the battleships.

Cruisers- the old Furtaka class is around, the Takao and Myoko classes are pretty well built out, and the Mogami's were being started, and the Tone class was maybe on the drawing board.

From a destroyer standpoint, you have the Mutsuki's, and old style class, and the the first of the new style destroyers withthe first power and weatherproof 5" turrets. All the rest of the destroyers had not been built yet.

Fighters are experimental mono-wing prototypes at this point, the Zero and the Claude are far in the future. Your attack craft is the B2M1, fresh in production with a speed of 132 knots, but it could carry 800kg of torpedoes or bombs.

At this point, what do you do? Here is a summary of a few things I mentioned, maybe a few other ideas.
1) Scrap the idea for the Yamato class, funnel this money into carrier development
2) Perhaps scrap the Fuso's and Ise's - I'm not sure what this would get you but even if it's maybe 20% the cost the vessel it's worth it.
3) Nagato's and Kongo's - continue with modernization, look at also ugrading the Nagato's power plant to give them the speed to keep up with the carriers, and least the Kaga and Akagi
4) Research an alternative torpedo for the deck stored torpedoes on the Heavy cruisers. Something less volatile than the type 93's.
5) Destroyers - these were excellent vessels for the most part. the 5"/50 gun though that just came into production - make sure it has the traverse speed and elevation to be a true dual purpose weapon. If it requires more weight, increase the tonnage on future destroyers to accomodate this. This would dramatically help Japan's fleet AA needs. Also, soon as the 3.9"/60 is available, try to get at least 1/3 of the destroyers armed this way, having an "AA destroyer" to accompany the carriers would be the role they fill. And get started on the Matsu class sooner - it's not a technological issue that prevented earlier deployment of these, just an indifference to sub defense.
6) Aircraft - pay more attention to self sealing fuel tanks, armor, armored windscreens. An ideal early war fighter would be a zero but with armor and self sealing fuel tanks, and sacrifice range, much like the later A6M3 Type 0 Model 32 version of the Zero. Changing the 2 cowl mounted light machine guns to 2 wing mounted 12.7mm's would be nice to, and it's not a huge increase in weight.
7) Submarines - Focus on diving depth and speed instead of size. The large behemoth Subs the Japs had were of little use, though keeping them as sub tenders as an idea. From a doctrine standpoint, use them to attack shipping and pickoff the occasional damaged warship as opposed to looking at them as part of the battle line.
8 ) The 25mm cannon - hard to say on this one, as even by the end of the war the Japanese still though it was an excellent weapon. Maybe they were right to some degree, but loading procedures need to be changed to increase the practical rate of fire to the 240 instead of 120 RPM. And a more substantial mount for the triple version might be needed to better handle the recoil/vibration. Getting a license or even ignoring patents to make the 40mm Bofors would be nice, but first they have to realize their 25mm is not up to par.
9) Depth charges - Pay attention to other navies and use the K-gun and Hedgehog or at least something similar.
10) Radar - research, beg, steal, spy, but make sure you are close to on par with other countries radar technology by the start of the war.


Another though as well - Pearl Harbor. It might actually be better to not attack Pearl and lure the US Fleet to battle to protect the Philipines. If they respond early in the war, say by first quarter of 1942, you will have a lot of advantages. Draw them close enough to the Philipines and your land based air will support you. The US AA capability by this time is nothing special. And the vessels, if sunk go to the bottom of the Ocean and are not repairable at Pearl. Given the ability of the aircraft, the quality of the pilots, and giving the Japanese 6 fleet carriers with the possible support from land based air and I'll take that any day over what the US fleet can do with maybe 3-4 carriers and Battleship Row. Just don't overcomplicate things, and keep your battleships with your carriers so they can help with AA fire.



If you happen to have the foresight at this point that these fragile airplanes that

I think the better hit rate by heavy guns has a lot to do with the inherently greater stability of the firing platform, plus the better accuracy of the range finding and fire control gear, whether it be radar assisted or purely optical, in the capital ships.

But even with all the accuracy in the world, actually hitting something at sea was to a big extent, a matter of luck, and luck increases the more times you get to roll the dice. Hence rof is a major determinant of hitting something

Part of the problem with scrapping and alternate construction were the different naval treaties. The Japanese did the best of any nation by far in hiding things, Like the Yamato construction but they weren't ordered until 1937.
Different classes of ships had different restrictions and the big 5 were watching to see what each other were doing.

Rebuilds could only be done on the oldest ships first and there were restrictions what was supposed to be done. Scrapping ships she didn't have to after fighting tooth and nail to keep them in the early treaty talks would have raised a few eyebrows.

Once Japan pulled out of the treaties all bets are off but that was not until the mid 30s and now you run into dockyard capacity problems, you can only rebuild so many old ships and build so many new ones at the same time.

parsifal said:

I think the better hit rate by heavy guns has a lot to do with the inherently greater stability of the firing platform, plus the better accuracy of the range finding and fire control gear, whether it be radar assisted or purely optical, in the capital ships.

But even with all the accuracy in the world, actually hitting something at sea was to a big extent, a matter of luck, and luck increases the more times you get to roll the dice. Hence rof is a major determinant of hitting something

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Yes, the big guns got the bigger rangefinders. Destroyers were lucky if they got a 3 meter rangefinder (and one at that). Battleships often had 11 meter or larger rangefinders and multiple ones. They sometimes averaged results or at least use the 2nd and 3rd range finders as double checks.

For a small change to make some extra resources available, why not have the IJN not start any of its development of midget submarines? AFAIK, Japanese midget submarines damaged two ships with torpedoes during WW2, HMS Ramillies and the tanker British Loyalty, which was a terrible return for the investment made. As well as avoiding adding useless equipment to many I-boats that would free up Chitose and Chiyoda to be converted to aircraft carriers before WW2.

In addition, although a submarine with a high submerged speed Submarine No.71 - Wikipedia, the free encyclopedia was tested pre-war, the idea of fast submarines capable of independent operation was initially rejected in favour of the use of midgets. Without the midgets, might a quicker development of an I-201 analogue have been attempted? The problem with both No. 71 and I-201 is that they needed German designed Diesels for adequate range. In addition, I-201 used the German ST-52 steel formula and German welding methods for a strong and smooth hull.

Unfortunately, I feel bound to add that the I-201 class were not ready for war by August 1945, so that making a choice to develop I-201 and purchasing the technology necessary from Germany in late 1938 (as soon as No. 71 had been tested), would leave it doubtful if the I-201 Class could take part in the early 1942 battles (OTL according to Wikipedia "The IJN General Staff made an official request for high-speed submarines in October 1943" I-201-class submarine - Wikipedia, the free encyclopedia).

Ah not correct. IJN midget subs were involved in at least 9 operations that I know of. Success was patchy, but then all of the major powers that developed midget subs experienced similar problems. They were essentially nuisance weapons, and in this, IJN midgets were about as successful as any of their contemporaries.

A really good source to get to know IJN midget sub operations can be found here

Imperial Submarines

As an example of the Midget sub operations of the Jpanase, I can cite many instances of their use, but one will suffice to illustrate

"Guadalcanal. At 0255, I-16 launches Lt ( j.g.) Hoka's midget submarine HA-10 about 3,000 yards NE from Lunga Point. At 0816, after penetrating a screen of destroyers, HA-10 fires one torpedo and damages Cdr (later Rear Admiral) James S. Freeman's (USNA '21) ALCHIBA (AK-23) that is starting to unload her cargo of aviation gasoline, bombs and ammunition. Freeman beaches ALCHIBA to avoid her sinking. She continues to burn for four days. After the attack, HA-10, Hoka and Inokuma go MIA. I-16 returns to Shortland".

parsifal said:

Ah not correct. IJN midget subs were involved in at least 9 operations that I know of. ...snip..

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Mea culpa! I apologise for not thinking beyond the initial Japanese advance. By looking through the details on the Combined Fleet site, I tried to make a list of the midget's successes. However, I do take the point that their main value may have been the need to guard against their attacks.

During the Guadalcanal Campaign, two USN ships, Majaba (AG-43) and Alchiba (AK-23) were damaged (Alchiba clearly very severely although she was repaired), whilst in the 1944-5 Philippines Campaign, the destroyer USS Renshaw (DD-499) was also torpedoed and damaged. In addition in the Philippines, the dock landing ship USS Shadwell (LSD-15) may have been torpedoed and SS Oliver Kelly was hit by a torpedo which did not explode. Finally, off Okinawa the destroyer USS Halligan (DD-584) was torpedoed by HA-67 and sunk. This seems to be the only clear sinking by the midgets although the tanker British Loyalty was damaged beyond economical repair.

I still think that the same design effort aimed at high speed submarines would have produced a greater return.

For sure, but it was Japanese submarine policy rather than equipment that was the problem. The best printed account of Submarine Operations that I know of is Carl Boyds and Akihiko Yoshidas book "The Japanese Submarine Force and WWII" by Bluejacket books. Western histories portray the Japanese submarines as not attacking Allied merchantmen, which isnt true. They would attack, and for about half their missions, they engaged in dedicated antishipping operations. in 1942, the 50 something strong submarine fleet sank more than 1 million tons of allied shipping.

But it was not a dedicated German style campaign centrally focussed and co-ordinated like the German effort, and significant resources were wasted on frivolous and often dangerous operations. Without a doubt the greatest waste of resources were the re-supply efforts and nuisance raids that were mounted. Fleet co-operation was the forte of Japanese submarines, but results were a poor return for the investment. Simply learning the German methods would have yielded the japanese a much better return for their submarines.

In the Barents Seas battle 31st Dec 1942, Hipper struck again hitting 3 times with 120 shells, crippling the destroyer HMS Onslow.

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The data in this case needs to be looked at more closely. Hipper first opened fire on the Achates at 0940 hours from a range of 14,900 meters (beyond visual range at the time), scoring a hit with its first salvo. However, its forward radar was knocked off line for about 50 minutes by a short in the ships power supply, and it ceased fire after only a few salvos. For the next 30 minutes or so it fired only few salvos in Kummetz's efforts to keep the British destroyers engaged with the Hipper, while turning the convoy into the guns of the Luetzow force approaching from the south. Then at 1016 hours the Hipper turned to bring its aft radar to bear and opened fire on the Onslow from 12,000 meters scoring four direct hits with an expenditure of only 48 rounds. Hipper then expended 51 rounds on Bramble for an unrecorded number of hits. At 1117 hours it opened fire on the Achates once again, from a range of 17,700 meters scoring a hit once again with its first salvo, followed by two more direct hits and several near misses in the next few minutes. Achates would later sink from the damages. Shifting fire to Obedient Hipper hit it and near missed it from a range of 11,600 meters. That's 9 direct hits that should be credited to Hipper during the battle.

If we look at the firing in segments it scored 4 direct hits on Onslow at night for the expenditure of only 48 rounds which is equal to only 6 broadsides. It scored 3 direct hits on Achates, from enormous range for 8" at night, with a like number of salvos fired. It almost scored one hit for each salvo fired each time it opened a dedicated fire using its radars.

Breaking up the firing into segments can give a better view of the hits scored per rounds fired at a given range, than looking at total rounds fired during the entire battle, because the ranges may vary and the condition of the ships firecontrol equipment can also vary greatly. For example, Exeter scored two hits on Graf Spee from a range of 19,400 yards by its third and fourth salvoes, or two hits per 18 rounds fired, or one hit for two salvoes fired. That is remarkable shooting, especially considering it had no radar, albeit the visibility was excellent. Then the Graf Spee started hitting the Exeter knocking out its turrets and it firecontrol and the ships command and control systems. Exeter scored no more hits despite a large expenditure of ammunition. Likewise Graf Spee's shooting was very good; scoring 7 direct hits and three damaging near misses on the Exeter alone during the first 15 minutes of the battle. Once Graf Spee lost its radar and its foretop rangefinder things changed, however.

Dont agree. The statistics presented are raw statistics and ought not be skewed by selective editing of this kind. German gunnery had a reputation for being very good, and that is reflected in the statistics already. If we start selecting the statistics like that, the purpose behind them is lost or prejudiced by our selective editing. If we are looking for average rounds per hit, we have to look at the whole package, and not go looking for the statistics that might make our favourite ship or nationality present in a better or ideal light.

There are instances that I know of where the British scored 1st salvo hits as well, but selecting statistics in that fashion will just serve to skew the overall results, and only serve mostly a propaganda purpose. Thgis discussion is not about the ideal, or the worst for that matter, its about total rounds per hit. For that we have to look at eveerything

The intent of these statistics was to show, in as complete a fashion as possible, how many rounds were fired per hit.

With regard to ranges, they will only vary firstly if one side has a speed advantage, or both sides are either trying to open the range, or conversely close the range. If the both sides have similar speed, and they have opposing range objectives (ie one wants to close and one wants to open), overall, there will be little or no effect on battle ranges). This is effectively what happened at north cape. Once Scharnhorst determined she wanted to disengage, it took a long time for her to open the range, because DOY was trying for the opposite

There are also conflicting reports about the number of hits actually achieved. these results appear to be based on German Admiralty after action reports, which by then were under considerable political pressure to produce a report in the most favourable terms. British admiralty after action reports do not corroborate these numbers of hits at all, although the RN admitted the loss of the MSW HMS Bramble, which is not even mentioned in the DKM report.

In other words, German records for this battle, as far as damage to enemy are concerned, cannot be relied upon.

They are actually compiled from the British reports.

I think the better hit rate by heavy guns has a lot to do with the inherently greater stability of the firing platform, plus the better accuracy of the range finding and fire control gear, whether it be radar assisted or purely optical, in the capital ships.

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As it has been shown, hits by the secondary armament from capital ships (usually 5" guns)was very poor as well, so the firing platform, while certainly a plus for big capital ships is not the answer as to why the 5" weapons had a lower hit rate.

As far as range finders go, the taller range finders on capital ships were for the main armament. Their secondary armaments used smaller range finders that were more akin to what you would find on a destroyer.

So, due to the lower accuracy of 5" guns on capital ships, and the facts above, you really cannot tie inaccuracy of 5" guns compared to cruisers or battleships main armament to the better firing platform and fire control.

But even with all the accuracy in the world, actually hitting something at sea was to a big extent, a matter of luck, and luck increases the more times you get to roll the dice. Hence rof is a major determinant of hitting something

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Equating hitting a ship to getting lucky on the dice is inaccurate.

Let's look at a 9 gun Cruiser. It with a salvo at 30,000 yards, gets a correction based on fall of shot, continues this for a few salvos and hits on the 4 salvo. This is about a 5 minute process to allow for fall of shot and adjustment. Was this because one of the shots "got lucky"? or was this a series of "educated guesses" if you would that were driven closer to their target by corrections of observed fall of shot?

I'd definitely say these were "educated guesses". When you have one moving ship trying to hit another moving ship miles away, and when you have to figure in things not covered by the firing solution, such as mount dispersion, there is indeed a bit of luck involved with hitting another vessel. But, it is not just a blind sot in the dark or a lucky roll of the dice. Feedback from fall of shot is crucial, which is why "straddling" a ship was so important. And repeated shots at a vessel will generally get closer and closer.

And in the above cruiser, 36 shots were fired for one hit. Does not sound great, but when you look at it as salvos instead, you have 4 salvos fired for one hit, and it is more common than not to only hit with one round even if 8-12 are being fired in a salvo.

To extrapolate it all to be a "lucky roll of the dice" and where firing as money shots as possible is not doing it proper justice.

Now, this heavy cruiser could fire as fast as it's capable of. That would be about 17 salvos, or 153 rounds. But I doubt you are increasing your chances of hitting, as you are only getting correction every 4 salvo or so. There is a reason why the fall of shot was waited for before firing the next salvo. And either all navies had this wrong, meaning that firing as many salvos if possible instead of waiting for fall of shot to correct, or your opinion on this matter is incorrect.

Now, it seems when ship got closer the rate of fire intensified. To what degree I am not sure, but it very well became faster than the time needed to fire, spot, correct, and fire. But this was at much closer ranges where the chance of hitting was much higher.

An apparently minor thing to do differently would be the development of aircraft carrier catapults. In 1934-5, Kaga was fitted with the only IJN design to be tested. I have heard a rumour that the design started from those already used to launch sea planes and that, unfortunately, the designers missed the subtle difference that, while sea planes need a trolley to carry them, the aircraft carried on a carrier have wheels. Thus the catapults on Kaga were launching the aircraft from trolleys rather than just pulling them. I suspect that they may not have been flush with the deck. Jon Parshall gave some information in an old post elsewhere "Air Technical Intelligence Group (ATIG) Report #1, p. 3, mentions that air catapults were tried, but set aside as being "too complicated and unnecessary." ATIG Report #5, page 6 describes a catapult fitted (presumably on Kaga) in 1935. It was compressed air, with hydraulic retardation, and apparently could reach a speed of 55 knots".

If we want to go really over the top, why not replace possibly the World's worse catapult designers by the best (i.e. Colin Mitchell)? Instead of using gunpowder or compressed air, why not realize that high pressure steam would be available on most carriers and could allow aircraft to be launched at a fairly fast rate as steam could be produced faster than air could be compressed. Of course, the designers would still need to design a mechanism that did not lose too much steam per launch.

Suddenly it is no longer so critical that Soryu, Hiryu, Shokaku and Zuikaku can run at 34 knots. What if we used Shokaku's machinery to drive two carriers at 28-9 knots? How would Coral Sea have worked out if the Japanese force had deployed four Centaur Class carriers Centaur-class aircraft carrier - Wikipedia, the free encyclopedia instead of the OTL Carrier Division 5? I suspect that a Centaur class ship without radar would cost about half as much as a Shokaku but I admit that the lack of a thick armoured main deck (127 mm ?) would create a potential vulnerability (only potential in 1942 as the USN didn't use armour piercing bombs until later).

Shokaku's hangars are longer than those of Centaur, partly at least because Centaur's catapults stop its hangar going too far forward, and partly because Shokaku is much longer than Centaur. Navypedia Shokaku aircraft carriers (1941) - Imperial Japanese Navy (Japan) gives the dimensions as "Upper hangar: 190.0x~20.0x4.8m, lower hangar: 160.0x~20.0x4.8m." whilst the Centaur Class hangar is normally given as 274 ft. x 62 ft. x 17.5 ft. The comparison is misleading because, while Centaur has two 54 to 55 ft. long elevators at both ends of the hangar which are not included in the hangar length, Shokaku's three elevators are included in its hangar length. However, even after excluding the space lost to the elevators, Shokaku has more than twice the hangar floor space of Centaur because of its double hangar (which would have restricted Shokaku from using post-war aircraft because of its lack of height).

Despite this, Shokaku was only designed to carry 84 aircraft, 12 of which were to have been stored as disassembled reserves. The RN planned to operate 42 aircraft from Centaur post war and those aircraft were much larger than 1941 IJN aircraft (the planned complement included, for example, Sea Hornets). Again it comes down to being able to launch with catapults. Aircraft can be parked on Centaur's deck because less space is needed to fly them off. It seems likely that 60 A6M2s, D3A1s and B5N2s could be operated from a Centaur without too many problems (apart from strengthening the aircraft for catapulting). There is a last point that Centaur had space for about 800 tons of aviation fuel (in service, 349,000 gallons of AVCAT AVGAS) in better protected tanks than Shokaku, which could only carry 500 tons (doubled to 1,000 tons for Taiho).

A nice feature is that you are now producing a cheap but effective design and can simply go over to large scale production when you realize that you need more.

For a related idea, OTL Japan laid down four training cruisers and completed three. Those weren't very useful in a war but at least they were cheap. Could Japan have chosen to build two very basic carriers with the idea of using the hangars as class rooms in peace time for training command? Probably they would want a few anti-submarine vessels as well, so that they could also teach cadets to run Diesel engines.

Garyt said:

There is a reason why the fall of shot was waited for before firing the next salvo. And either all navies had this wrong, meaning that firing as many salvos if possible instead of waiting for fall of shot to correct, or your opinion on this matter is incorrect.

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This was not the doctrine of the USN for cruiser fire and part of the reason why USN cruiser shooting was so awful. The USN adopted the doctrine of shooting as rapidly as possible and walking their salvo pattern back and forth over the target. USN cruiser shooting is remarkable for how poor it was. Didn't matter if it was day or night or with or with out radar-it was terrible. Walking salvos also spilled over into battleship shooting practices as well.


Apparently the Hipper was practicing more deliberate fire methods.

The best chances for scoring at least one hit from a straddling salvo occur when the range has dropped to about 60% or less the max ballistic range of the guns.

Interesting thought, Cherry Blossum. Sounds like you are saying is the need for the Japanese fleet carriers size was largely due to the need of having a long enough area for takeoff?

Another very minor alteration to the carriers that would have helped - open hangars. An open hangar allows planes to warm up down below, allowing a quicker launch. It also makes it easier to jettison ordinance off the side of the ship in the event of a fire. Explosions on the hangar deck would be contained less, which is a good thing, the explosion can vent itself to the open air easier than if it is contained more in a closed hangar design. It also allows other ships to assist better when it comes to fighting fires, and allows the hangar deck to aerate easier to avoid explosions from built up avgas vapor, such as what happened to the Taiho. And yes, you can have an armored deck over open hangar construction if you wish.

I suspect that a Centaur class ship without radar would cost about half as much as a Shokaku but I admit that the lack of a thick armoured main deck (127 mm ?) would create a potential vulnerability (only potential in 1942 as the USN didn't use armour piercing bombs until later).

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It did not take AP bombs to penetrate an unarmored deck - GP bombs would generally explode on the hangar deck of an unarmored carrier. And a bomb exploding on the Hangar deck was generally what was so damaging to aircraft carriers, happened to the Akagi, Kaga and Soryu at Midway and to the USS Franklin and Bunker Hill later in the war. The Japanese without radar did not know US bombers were coming, and with the Franklin and Bunker Hill the US did not want to shut down flight operations everytime a few bogies were detected on radar.

Only Japanese Carrier to have an armored deck was the Taiho, and the US to my knowledge did not have an armored deck carrier comissioned prior til war's end, only the Midway about 8-10 days too late.

And with an armored flight deck, even most armor piercing or semi-armor piercing bombs would not pierce the deck when dropped at dive bombing altitudes. Depends a lot on the thickness of the deck of course and the type of bomb.

This was not the doctrine of the USN for cruiser fire and part of the reason why USN cruiser shooting was so awful. The USN adopted the doctrine of shooting as rapidly as possible and walking their salvo pattern back and forth over the target. USN cruiser shooting is remarkable for how poor it was

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Interesting Wavelength, and that makes sense. I was not aware that anyone would rapid fire from range - I knew as they got closer they would, but not from range. How about US destroyer practices? Same as US Cruiser practices?

and part of the reason why USN cruiser shooting was so awful.

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That's my point - firing as fast as you can without receiving corrections has a strong negative effect on accuracy. It also cause crew fatigue, but that's a different matter.

The best chances for scoring at least one hit from a straddling salvo occur when the range has dropped to about 60% or less the max ballistic range of the guns

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So about 18-19k yards for a cruiser? I would think though the initial attempts and keeping the vessel under fire starting at longer ranges would help, as long as you are within rangefinder range (or if radar is effective)?