Midway with expanded Kido Butai?

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There seems to be some cherry picking of information about a Wasp v other carriers in the above comparisons.

Pre-war everyone's carriers were limited by the constraints of the various Treaties. That meant:-
1922-1936 a total tonnage limit (135,000 for US & Britain, 81,000 for Japan). The US enshrined that in domestic law which they only increased by 40,000 tons in Second Vinson Act in 1938, when they didn't need to for international purposes. That US increase allowed the building of Hornet, and an allowance towards Essex.

Add to that limits on individual carrier size (27,000 to 1936, 23,000 thereafter with exceptions for Lexingtons & Akagi & Kaga) but subject to the overall limit.

Wasp was designed to use up the the available Washington tonnage after taking account of what was available by converting Langley CV-1 to a seaplane carrier as permitted by the Treaties, prior to the expiration of the Treaty on 31 Dec 1936. She was being designed when Second London Treaty was being discussed and negotiated and laid down 1 April 1936, just days after that Treaty was agreed. By that time the Japanese had announced their departure from the Treaty system

So here are some numbers from my sources incl Friedman US Aircraft Carriers

Wasp
Standard displacement 14,700 tons
Full load displacement 19,116 tons
Flight deck 727x93 feet
Hangar deck 522x63 feet
Airgroup - 74

By early 1942 her air group consisted of 18xF4F-3, 30xSB2U-2 & 6 TBD-1, total 54. By swapping out the fixed wing F4F-3 for folding wing F4F-4 later in the year and moving to SBD-3 and TBF-1 she was able to increase the airgroup to c65.



Commencement Bay class
Standard displacement ? (Wiki says 10,900 tons)
Full load displacement 21,397 (design 24,275 tons)
Flight deck 501x80 feet
Hangar deck 216x69 feet
Airgroup - 33 (18xF6F, 15xTBM-1)

The Commencement Bay was based on a modified tanker hull, not that of a purpose designed carrier. It would therefore be less efficient space wise for a given tonnage. Unlike a purpose designed carrier the hangar ran for a much shorter length due to the need to accommodate other things. Much of the space under the flight deck aft was taken up with machinery & crew spaces

And for the Japanese ships from the Kagero book on the pair
Soryu (as completed 1937)
Standard displacement 15,900 tons
Full load displacement 18,800 tons
Flight deck 712x85
Hangar deck ?
Air-group - 71 (55 + 16 spares) - A5M4 Type 95 fighters (12+4), B5N1 Type 97 TB (9+3), D1A2 Type 96 dive bombers (27+9), 7 C3N Type 97 recce

Hiryu (as completed 1939)
Standard displacement 17,300 tons
Full load displacement 20,250 tons
Flight deck 712x89 feet
Hangar deck ?
Air-group - 73 (as Soryu + 2 additional C3N)

By 1941, with increasing aircraft size, the air groups comprised 21 A6M, 18 B7N & 18 D3A. Total 57.

It is important to note that Japanese carrier capacity, like that of Britain, was determined by hangar capacity. USN SOP involved deck parks even in pre-war days, thus increasing the numbers able to be carried by a ship of comparable size. And both Japanese ships were designed to be faster than Wasp requiring more powerful machinery. They had over double the installed shp giving an extra 4 knots or so in top speed.

As for the Essex class being a pre-war design, it depends on when you consider WW2 started, 1939 or 1941

The design process started in May 1939, after Hornet was ordered, when there was only 20,400 tons to play with. The design characteristics weren't signed off until Feb 1940 by which time, unfettered by Treaty considerations from Sept 1939, the design had grown to 26,500 tons standard. It would continue to rise the final 27,100. The Two Ocean Navy Act of mid 1940 allowed the US to build multiple ships of that size. That size increase was intended to provide the capacity for a full 5 squadrons of 18 planes each, but of the much larger & thirstier aircraft being designed for them. Those were the F4U, SB2C and TBF.

The Japanese without Treaty restrictions, moved to a much larger vessel of 26,675 tons standard with the Shokakus laid down in Dec 1937 & May 1938.
 
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Bending the keel is complete nonsense. To heat steel in contact with the heat sink of the ocean to the plastic deformation temperature of steel is physically impossible. What is your source for this?
 
None of the Illustrious/Implacable class were "written off" or "constructively wrecked".

Formidable was the only one to see no service after completing trooping trips in Feb 1947. But after being repaired in 1941 she served through to 1945 when she suffered two kamikase hits. She was laid up largely unmaintained and was found to be in such poor condition in 1949 that Victorious replaced her for modernisation. But despite all the comments about bent keels, no one has thus far produced any documentary evidence to confirm it. She was the first to be scrapped in 1953.

Illustrious, bombed off Malta in Jan 1941 and probably the worst damaged of all, survived the war despite further damage in 1945 from a kamikaze near miss. Refitted 1945/46 she became a trials and training carrier, continuing in the role until the end of 1954.

Indomitable, bombed in 1942, repaired and torpedoed in 1943, repaired again and kamikazied in 1945 (without the flight deck being penetrated). In reserve 1947-50 she was refitted and served as the Home Fleet flagship before being laid up again in 1953, as the next generation carriers began to enter service.

Post war manning problems meant that they RN preferred to keep the light carriers as operational carriers rather than the armoured carriers, except for Implacable and then Indomitable 1946-53.

As for the Malta class design, it was never signed off by the Admiralty. It began life as a double hangar armoured carrier design, like a bigger Audacious class before a redesign was ordered and the final unarmoured open hangar was produced.

And before being too critical of British carriers just remember both the IJN and the USN adopted the armoured flight deck. While the Midway class remained an open hangar design the hangar sides were protected by the armour of the 5"/54 pedestals. However in comparison with previous US carrier designs, there were far less openings in the hangar sides due to the need for much greater supporting structure for the armoured flight deck. But of course that design was never tested in the same way as the Illustrious class.
 
Reluctant Poster said:
Bending the keel is complete nonsense. To heat steel in contact with the heat sink of the ocean to the plastic deformation temperature of steel is physically impossible. What is your source for this?
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This got me thinking about my experiences in the utility business. A big coal fired boiler has a furnace made up of waterwalls which are steel tubes with fins welded to them. The fins are butted together to make an airtight enclosure, the required air for combustion is fed by a number of large fans. The remarkable thing about water wall construction is that the walls are cooled by water running through the tubes at or near boiling point. In a typical 500 MW utility boiler the water pressure is ~2600 psi. Water at this pressure boils at 674 F and this is the cold side of the tubes! The tubes are made of ordinary carbon steel not some super alloy. I compared the composition of SA-210 which is a typical tube material with that of Ducol which is the steel used in British warship construction (and post war merchant ships) and found them to be very similar. Further research found that Ducol has actually been used in boiler pressure parts. Obviously, the steel used in the construction of the carriers can withstand very high temperature without deformation. The idea that a hanger fire could distort the hull is complete nonsense.

 
Macandy said:
A significant design advantage US carriers enjoyed was their open hanger decks. Explosion and fire was vented, rather than contained.
Click to expand...
This myth has been debunked previously in this forum. Others have posted images of US carriers with flight decks bulged up. This does give me the opportunity of reposting the image of Enterprise "venting" most of her forward elevator 400 feet in the air.
 
I should also have stated the origin of the Formidable hanger fire myth. I have seen this on the internet different forms. Some state a Firefly accidentally discharged its 20mm cannon, others that a Corsaires 's 50cal started the fire. According to Stuart Slade in the anti armoured carrier screed he wrote on the Navweps website the fire occurred and "The heat deformed the hull and that was it." The implication is that it was scrapped shortly after this incident. If this were true the incident occurred post war.
The reality is quite different. There is a kernel of truth in that there was a hanger fire on the Formidable on May 14, 1944. The fire took an hour to put out because the fire curtains had been rendered inoperable by the Kamikaze attack on May 4. Note that the sprinkler system worked indicating it wasn't distorted by the fire. Repairs were undertaken at Sydney as part of a general refit which took a month which was was not unusual (US carriers struck by Kamikazes often went back to the west cost for repairs being out of action for three months, some were repaired at Ulithi taking a month). I compiled a list of kamikaze attacks on US carriers and the time taken to repair them. Note that the 3 months out of service included transit time. Repair likely took about a month.
 

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Here's the USN verdict on venting:


This from


I took the plan of the Yorktown (similar to Enterprise) hanger and superimposed the damage suffered by the Enterprise to illustrate the effect of the explosion. Note the flight deck was bulged (up to 5') directly above the side vents and downstream of the forward elevator. Blast damage occurred for much of the length of the hanger.

 
Again: the kamikaze's bomb went down several decks and detonated in the elevator well.
This amplified the blast as it was in the well, the explosion had no where to go but up. This how the elevator was thrown clear of the ship.

Here is a link that covers the kamikaze impact, explosion and damage detail, complete with actual diagrams of the damage.

Operations of Kyushu - Battle Damage

Battle damage inflicted on USS Enterprise CV-6, 14 May 1945, off Kyushu, Japan.
www.cv6.org
 
The website you reference is the one that piqued my interest in the effectiveness of venting (or lack thereof). In particular this statement caught my attention:

The website states that it is the damage report of 14 May 1945 but obviously it is not the full report, therefore I went to my collection of USN damage reports and found the one I referenced "USS Enterprise (CV-6) War History". This turned out to be the same report referred to on the website.

The following are excerpts from the original report:


Note that the flight deck was damaged all the way back to Frame 70




in the right-hand side of the photo you can see the elevator opening.


I have revised my markups of the Yorktown drawings to make it clear that the flight deck bulge was directly above the side openings. The pressure wave from a high order explosion moves in a sphere from the center of the explosion. Each portion of the wave continues to move in a straight line until it hits something. There is no mechanism for a segment of the wave to know that there is a path of less resistance to it to follow. There is a direct line from the explosion to the flight deck. That portion of the pressure wave followed it original trajectory and went right past the elevator and side vents and struck the flight deck with its full energy. It can't make a right angle turn to go out the side vents.



The conclusion of the report is quite unequivocal:
 

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That's some fascinating insight. In some other discussion on Midway i've run into some people that are absolutely adamant that the fires on the japanese carriers distorted the hulls, hence making them unrepairable even if one or more of them somehow make it back to Japan. So this idea can be considered debunked and put to rest then?
 


This photo from the Australian War Memorial shows the damage to HMAS Hobart from a torpedo hit.

As has been noted in this thread already the explosion went up and the bent up part is the actual deck.
All repairable and could have been worse. Not a carrier but the effect is clear.
 
The damage that the Japanese carriers suffered at Midway is described in some detail in "Shattered Sword". The damage that they suffered was far more than just fire damage. I'll try to summarise:-

Kaga
Hit by 5 bombs (4x500lb & 1x1,000lb). One on the bridge and 4 spaced out from the forward to after lifts in the upper hangar, destroying the fire mains. Not only was there some 10,000 gals of fuel in the tanks of the aircraft located there to fuel the fire but the ship's aircraft fuelling system was not secured when the bombs hit and so it contributed more petrol to the fire. There was then the lose aviation ordnance in the hangars, estimated to be 80,000lbs of bombs and torpedoes, none of which could be jettisoned, much of which was being cooked by the fire. That triggered a massive fuel-air explosion followed by 6 others that blew out the hangar sides.

There is an artist's rendition of the Kaga immediately before being scuttled later that day. While her lower hull appeared intact the fire and explosions had chewed their way down to the level of the lower main deck with the casemates for the 8" guns. Note the smoking black hole from the island to the aft end of the hangar all the way down to the lower main deck that was still burning. Parshall & Tully expressed the view that even if she could be towed home she was not repairable.


One advantage she had over the other carriers was that there were a greater number of decks between the lower hangar deck and the deckhead of the machinery spaces, so they could remain manned for longer before smoke and heat caused their abandonment. 2x24" Long Lance torpedoes put an end to hr suffering.

Soryu
Hit by 3x1,000lb bombs along the length of the hangars (two in the upper & one in the lower). So both her hangars were immediately ablaze from burning aircraft fuel. It then wasn't long before the fires worked their way down to the deckheads of the engine rooms. She very quickly lost power and was soon on fire from end to end and had to be abandoned within about 15 mins of being hit. Being of generally lighter construction than Kaga those 1,000lb bombs would have done some structural damage but limited to areas above the waterline. Then more damage would be inflicted by her own ordnance cooking off within the closed hangar spaces wreaking further structural damage.

It took 3x24" Long Lance torpedoes to finally sink her.


Akagi
Was only hit by a single bomb just aft of the mid-ships lift but it wrecked the fire curtains there and allowed flaming debris into the lower hangar. But there were rwo near misses, the aft one which may have caused extensive shock damage to the after part of the ship and preventing the aft magazines being flooded as well as damaging the rudders, something that was only discovered a short time later as she tried to manoeuvre. But the midships area of the upper hangar contained 18 fully fuelled B5N2 Kates armed with torpedoes and the bomb landed squarely on the first of those. After only some 3 minutes after the US dive-bomber hit her own ordnance started cooking off multiplying the then existing damage enormously. Add to that that the CO2 fire protection system had been damaged and rendered ineffective. So a fire that might have been able to be confined to the upper hangar gradually worked its way deeper with smoke being drawn into the machinery spaces and causing their abandonment.

But it took several hours for things to become hopeless. Any towing attempt would have encountered difficulties with her damaged rudders. And the engine room crews couldn't get back into the machinery spaces due to the heat & smoke. It finally took 3 Long Lances to sink her.


Such were the fires in these three ships that the casuasty rate amongst the engineering personnel was huge, with only a few escaping Soryu & about two thirds being killed in Kaga. Akagi's engineers suffered less due to her damage taking longer to develop & orders being given to evacuate these spaces when her steering failed.

Hiryu
She was hit by 4x1,000lb bombs along the forward third of her flight deck, three of which exploded in the upper hangar amongst 19 Zeros. Fires broke out immediately and the forward flight deck rapidly collapsed into the hangar. The fourth completely destroyed the forward lift. Although her damage control was better than the others the fires were fanned aft by virtue of her pushing on at 30 knots to avoid other attacks. By the time these had ended she was already on fire from stem to stern but was still able to move at 28 knots. Not only did the paint burn of the deckheads in her machinery spaces, but they slowly turned red and began to glow. Eventually they had to evacuate the compartments and the ship ground to a halt. Her own firefighting efforts over many hours plus those of the escorting destroyers when she finally stopped pumped so much water into the hull that she developed a 15 degree list to port. Two and a half hours after stopping she suffered another huge internal explosion which rekindled the flames.

This is Hiryu the next morning still burning. Note the completely destoyed flight deck forward (to the right of the photo. Her island was on the port side rather than the traditional starboard side. The object in front of the island is part of the destroyed forward lift.)

Summary
We really don't know what the material state of these ship's hulls before they were finally scuttled. The fires had penetrated at least as far as the deckheads of the engine room spaces and in Soryu's case penetrated into some engineering spaces. But this was still generally above the waterline. They had all at the very least been completely gutted internally above the waterline. Except for Kaga we don't really know how much the ships' structures had been affected internally by the initial bomb hits or by the subsequent internal explosions.

As for salvaging them, the first problem would have been getting enough crew aboard to control the fires and establish a tow. They were all still burning when scuttled. How long would they have had to wait to allow fires to die down before attempting to reboard (a handful were abandoned on the Hiryu). Akagi would have been a pain to tow with her damaged and jammed rudders.

Even if they could be got home, then the next problem would have been finding the dockyard space and materials to repair them. Japanese plans for Ise & Hyuga had to be curtailed due to lack of materials. They would needed stripped down to the top of the machinery spaces. and rebuilt. How long would that take? Well if we use the example of the light carrier conversions Zuiho, Shoho, Chitose & Chiyoda, they took about 12 months each but were much smaller ships. So probably getting up towards 2 years. And the Japanese were building the Unryu class, very similar to Hiryu, in about 2 years. Would it actually have been worth it?
 
I am familiar with the book, though as i pointed previously i don't necessarily agree with some statements in it and do not consider it the last word on Midway, but thanks for taking the time to compile this resume.

To answer to the last question, imo yes, even two mangled carriers worth their weight in gold. If for instance the time/efforts and materials from the building/ conversions of Shinano, Ibuki and the 2 Hyugas (which imo were a waste of material and yard space) are redirected instead to repair/rebuild say Hiryu and Akagi (the most salvageable of the IJN Midway CVs imo - and since this is an ATL i can't but give them a bit more luck to make them more salvageable*), that's a net gain because Akagi and Hiryu will at least be ready for say the Marianas battle, while the 4 aforementioned ships contributed nothing to the war effort, incomplete Shinano was sunk in it's first sortie after an insane amount of work, materials and hope have been put into it, Ibuki was never finished, while the Hyuga conversions achieved nothing, better to have kept the rear guns (perhaps only 10 on Huyga, as one rear turret was landed due to explosion in May 1942, it may or may not be repaired and put back if not converted to BB-XCV), at least they could have lobbed more beehive shells at the american aircraft.

At least Akagi and Hiryu would have launched against their USN nemesis once again, at the Marianas and/or Leyte.

Btw, one option studied was to float Shinano's hull as early as possible, planned for October 1942 i believe, to free the drydock. I guess same accelerated launch could happen with Ibuki's hull, just to get it out of the way. As to the available repair space as of mid-1942, well Shokaku is just finishing repairs at Kure, so let's say Hiryu can then take it's place. While at Sasebo, the huge new repair drydock built for the Yamatos (and apparently used only once) could be used to repair Akagi if free.

Regarding repair times, post Midway plans for converting BBs to full CV were estimated at 18 months, while for CAs at 9 months. As i expect the japanese would move heaven and earth to repair Hiryu and Akagi, i think 18 months for Akagi and say 12 for Hiryu are realistic, and imo still a bit on the pessimistic side.

*Let's suppose for a moment Akagi's rudder is not damaged, either the near miss bomb at the rear lands wider or it actually hits the rear deck as older sources claim, while for Hiryu let's say her last strike is launched at 16.30 as initially planned despite the tiredness of the air and ship crew, so there are much fewer armed and fueled planes to burn/explode.

PS: Of course, as this ATL could involve a different OOB, if say Zuikaku is at Midway one can build a scenario in which Zuikaku herself as well as Akagi and Hiryu are not even touched by bombs, i may have expanded on this idea previously iirc.
 
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A question regarding a hypothetical post-Midway period, in which maybe the japanese did not lose as badly as OTL, or get a draw etc. If let's suppose they don't feel quite as hard pressed by circumstances to convert any suitable (or not) hull to CV/CVL/CVE, do you think they could finish the Shinano as a battleship-carrier (same arrangement like the OTL Hyugas), and the Ibuki as an aviation cruiser (like the Mogami conversion), in time for the rough period of the Leyte naval battles? To free yard space and resources, the Hyugas are not touched in this scenario, they remain full battleships.

OTL for Shinano there were 7 guns in various assembly stages and two partially finished turntables, hence the proposed BB-XCV conversion for this ALT - Shinano. I assume that the japanese wouldn't have the resources to built a few more 46cm guns and the rear turret, but only focusing on finishing all the 7 guns already started and the front turrets, with a seaplane deck at the back like the Hyugas. Also OTL the CV conversion was greatly delayed by first, having to actually design the conversion, and secondly by overworked shipyards with conversions, battle damage repairs etc.

Similarily for Ibuki, the yard space at Sasebo was hogged up by one of the Hyugas, hence starting conversion only in late 1943 after being left idle for something like half year. On japanese wiki it says when they started the CVL conversion they had to first remove some turrets and half the machinery, so the work on it must have been quite advanced when stopped with some turrets and the machinery installed? In this scenario Ibuki is taken straight to Sasebo after launch in May-June 1943.

Would it be quicker to finish these two ships as i propose?

Also, do you think there's a reasonable way to avoid Mutsu blowing up in 1943? Was it really a disgruntled sailor or an unstable ammunition explosion that doomed it, anything new came up on the subject?
 
mack8 said:
Also, do you think there's a reasonable way to avoid Mutsu blowing up in 1943? Was it really a disgruntled sailor or an unstable ammunition explosion that doomed it, anything new came up on the subject?
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There must have been a bunch of disgruntled sailors around the world.
from the early 1890s to end of WW II more battleships (pre dreadnought and dreadnought) had blown themselves up with their own ammunition that had been sunk by enemy gunfire.

Admitting that old, or improperly stored, ammunition can burn/explode without outside intervention it not good for morale.

Walking (or swimming) away from a major magazine explosion is rather rare.
 
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