Were The Japanese Ocean Liners Converted To Aircraft Carriers A Waste Of Resources?

Obviously, to have this ATL working you gotta have the IJN train proportionally more pilots for these larger CVs.

And the IJN had the resources to do that. But what it did not have the capacity to do was expand its carrier arm while at the same time throwing 8,000 aircraft away in the Solomons between 1942-1944. If committed to a carrier air wing strategy the IJN had to devote more of its resources to training and less to the Solomons in 1943.

As For Shokaus and Taiho etc. actually at Pearl Harbour apparently all japanese CVs carried the maximum they could operate (Kaga and Shokakus 72, Akagi 66 or 69, Soryus 57, plus spares). Shokakus again carried 72 each at Eastern Solomons. There was definitely a shortage at Coral Sea and Midway though.

Hawaii -
Kaga - 21, 27, 27 = 75
Sho/Zuikaku - 18,27,27 = 72
Akagi - 21, 18, 27 = 66
Soryu/Hiryu - 21,18,18 = 57.
 
Thanks for that Glenn.

As to the auxiliaries, it appears that indeed there was a limit of 10,000 tons for any other warship than a BB or CV, so they can't be made 50% larger unless they just cheat, but then they did that with Soryu and Hiryu so why not?

Still though, after reading a bit more, i'm more baffled than before why they have ordered Junyo and Hiyo insted of two proper carriers. They knew that the Vinson act of 1938 allowed for two 20,000 tons carriers, and apparently an immediate response to this US plan was to convert Zuiho (and maybe Shoho, but have to re-check). Also apparently the initial planning for Maru 4 keikaku included 2 BB and THREE CVs, but in the end they only ordered Taiho. Perhaps this has to do with the China war and limited funding as the army was appropriating as much as they could.

Still, the thing is, if they wanted two CVs to carry 53 (48 operational) aircraft each, they could do it on 15,000 tons or less and like i pointed earlier such a ship could go easily to 28-29kt, this not only being able to fully work with Kido Butai, but also saving almost 20,000 tons of steel! But such a ship can easily carry as many aircraft as Soryu, so it's a win-win. The worse thing is the Junyos were built on military slips, thus blocking them from building two real warships. At least if they would have been built in some civilian yard those slips could conceivably be open and used for two appropriate size warships of any type, be it CVs or CAs, anything from Maru 4.

But hindsight is a wonderful thing.
 
Taihō's upper and lower hangars were approximately 150 m (492 ft 2 in) long and 5 m (16 ft 5 in) high. The upper hangar was 1 m (3 ft 3 in) wider than the lower. Fighters were normally stowed in the middle and forward sections of the upper hangar and were raised to flight deck level using the bow elevator to facilitate more rapid handling. Dive bombers occupied the remaining upper hangar spaces with torpedo bombers stowed in the lower hangar. With greater all-up weights and longer take-off runs than the fighters, these planes were brought up to the flight deck using the aft elevator where they could then be spotted as far astern as possible

The Shōkaku-class carriers' 242.2-meter (794 ft 7 in) flight deck had a maximum width of 29 meters and overhung the superstructure at both ends, supported by pillars. Ten transverse arrestor wires were installed on the flight deck that could stop a 4,000-kilogram (8,800 lb) aircraft. If the aircraft missed those, it could be stopped by one of three crash barricades. Although space and weight were allocated for two aircraft catapults, their development was not completed before the Shōkaku-class ships were sunk. The ships were designed with two superimposed hangars; the upper hangar was about 200 meters (656 ft 2 in) long and had a width that varied between 18.5 and 24 meters (60 ft 8 in and 78 ft 9 in). It had a height of 4.85 meters (15 ft 11 in) while the lower hangar was 4.7 meters (15 ft 5 in) high and only usable by fighters. The lower hangar was about 20 meters (65 ft 7 in) shorter than the upper one and its width ranged from 17.5 to 20 meters (57 ft 5 in to 65 ft 7 in). Together they had a total area of 5,545 square meters (59,690 sq ft).[6] Each hangar could be subdivided by five or six fire curtains and they were fitted with fire fighting foam dispensers on each side. The lower hangar was also fitted with a carbon dioxide fire suppression system. Each subdivision was provided with a pair of enclosed and armored stations to control the fire curtains and fire fighting equipment.

The Shōkaku-class carriers were initially intended to have an air group of 96, including 24 aircraft in reserve. These were envisioned as 12 Mitsubishi A5M ("Claude") monoplane fighters, 24 Aichi D1A2 ("Susie") Type 96 dive bombers, 24 Mitsubishi B5M ("Mabel") Type 97 No. 2 torpedo bombers, and 12 Nakajima C3N Type 97 reconnaissance aircraft.[10] All of these aircraft were either superseded by larger, more modern aircraft or cancelled while the ships were being built, so the air group was revised to consist of 18 Mitsubishi A6M Zero fighters, 27 Aichi D3A ("Val") dive bombers, and 27 Nakajima B5N ("Kate") torpedo bombers.[11] In addition, the ship carried 2 Zeros, 5 "Vals", and 5 "Kates" as spares for a total of 84 aircraft.

Taihō's planned air complement varied considerably throughout her design and construction. Initially, it was envisioned she would carry 126 aircraft (with 30 of these in reserve). Later, this was pared down to 64, raised again to 78 and finally reduced to 53. One reason for the discrepancy in numbers was (in sharp contrast to the United States) the Imperial Japanese Navy's lack of insistence that its carrier planes have the smallest possible folded wingspan (many designs' folded only near the tips, while the wings of the Yokosuka D4Y Suisei dive-bomber did not fold at all). Her aircraft capacity was also changed based on previous wartime experience and the fact that Taihō was expected to carry larger newer-model carrier planes still under development at the time of her construction: 24 Mitsubishi A7M2 Reppu "Sam" fighters, 25 Aichi B7A2 Ryusei "Grace" torpedo bombers and four Nakajima C6N1 Saiun "Myrt" reconnaissance planes. As none of these types were available at the time of her commissioning, Taihō went to sea with older-model aircraft.

I stand corrected about the two level hangar (i'm sure i read something like that, maybe it was about Shinano?), as for the variation of Taiho's airgroups, according to a book on Taiho it seems the first one for 126 was only the number provided to the finance ministry so as to impress (as in give them the money for the ship).

On the other hand in Kojinsha i read the initial airgroup was planned for 63+15 (total 78) A5M/D3A/B5N, later updated to 60+1 (61) A7M/B7A/C6N, of which 13 were in a deck-park.
 
Thanks for that Glenn.

As to the auxiliaries, it appears that indeed there was a limit of 10,000 tons for any other warship than a BB or CV, so they can't be made 50% larger unless they just cheat, but then they did that with Soryu and Hiryu so why not?

Still though, after reading a bit more, i'm more baffled than before why they have ordered Junyo and Hiyo insted of two proper carriers. They knew that the Vinson act of 1938 allowed for two 20,000 tons carriers, and apparently an immediate response to this US plan was to convert Zuiho (and maybe Shoho, but have to re-check). Also apparently the initial planning for Maru 4 keikaku included 2 BB and THREE CVs, but in the end they only ordered Taiho. Perhaps this has to do with the China war and limited funding as the army was appropriating as much as they could.

Still, the thing is, if they wanted two CVs to carry 53 (48 operational) aircraft each, they could do it on 15,000 tons or less and like i pointed earlier such a ship could go easily to 28-29kt, this not only being able to fully work with Kido Butai, but also saving almost 20,000 tons of steel! But such a ship can easily carry as many aircraft as Soryu, so it's a win-win. The worse thing is the Junyos were built on military slips, thus blocking them from building two real warships. At least if they would have been built in some civilian yard those slips could conceivably be open and used for two appropriate size warships of any type, be it CVs or CAs, anything from Maru 4.

But hindsight is a wonderful thing.

Is the 10,000 tons you quote the clause in the Washington Treaty that says any warship over 10,000 tons or armed with guns larger than 8" is a battleship and therefore its displacement has to be taken out of the tonnage quota for battleships?

If that is the case it (IIRC) only applied to warships and not auxiliaries. The British built at least one auxiliary larger than 10,000 tons whilst the treaty restrictions were in force and Jane's Fighting Ships 1939-40 says the Japanese have about 10 oilers displacing 14,050 tons that were built in the 1920s.

It gives the displacements of the 3 seaplane carriers ordered in 1934 as 9,000 and Nisshin ordered in 1934 is not mentioned. The older seaplane carriers Kamoi and Notoro, which were converted oilers are listed as 17,000 tons and 14,050 tons respectively.

The submarine depot ship Taigei, the future Ryuho, has a standard displacement of 10,000 tons, but Turagizaki and Takasaki (The Unspellables) the future Soho and Zuiho (but not necessarily in that order) are given standard displacements of 12,000 tons although their dimensions were smaller than their predecessor.
 
Just some quick thoughts:
Is the 10,000 tons you quote the clause in the Washington Treaty that says any warship over 10,000 tons or armed with guns larger than 8" is a battleship and therefore its displacement has to be taken out of the tonnage quota for battleships?

Yes that is what i had in mind. When you can, could you please send me the London Treaty text too, i think you were mentioning both but i only seem to have received the WT. Thanks a lot.

On another subject touched earlier, i.e. just ordering two Shokakus instead of Junyos, i had another look at the info on slips etc. So it appears that indeed Hiyo can be replaced by another Shokaku or even Taiho itself if the design is ready by late 1939 (it was approved for construction in early 1939, but not sure if the detail design would have been ready in time for this ATL)
As for the Junyo, it appears the Mistubishi-Nagasaki slip it was built was the shorter 225m one, the other 275m one was building the Musashi. So if they don't order Junyo they can build an Unryu type instead. I would still have an Unryu over Junyo any day though.

Actually, come to think of all this, the navy does not even need more money or anything to build these ships, the 60% that the navy was paying from the cost of the two Junyos can easily buy Unryu i would think, while Taiho was already being paid for. The only issue that might be problematic is the machinery for them, but in theory they could just fit the Unryu with twin destroyer turbines, it will be still a formidable 32kt fleet carrier. Those slips will then be available in mid to late 1941 to start building ships from Maru 5, or just from the 1941 supplementary program, anything they wish!

To kinda paraphrase another subject, an Unryu is worth two Junyos.
 
To kinda paraphrase another subject, an Unryu is worth two Junyos.

Strategy is the successful comparison of apples to oranges. Which is more valuable? Speed, mass, or ability to take damage? I'd propose a formula something like this -

Aircraft carried * speed + tonnage / 100.

Junyo = 54*25+25000/100 = 1600
Unryu = 57*34+18000/100 = 2118
Zuiho = 30*28 + 12000/100 = 960

For defensive missions speed would not be as important. So for offense an Unryu might be worth 1.3 Junyos, for defense they're about even.
 
Characteristics of Japanese Auxiliaries

I was looking up the IJN's tanker force in my copy of Jane's Fighting Ships 1939 this afternoon, something about the Unspellables (which were on the next page on their submarine tender configurations) caught my eye.

The future Ryuho, has diesels producing 13,000 bhp for 20 knots. The future Soho and Zuiho have diesels of 13,000 bhp too, but they have a maximum speed of 19 knots.

I checked that against Warships of the Imperial Japanese Navy 1869-1945. According to that Taigei had 4 diesels producing 14,000 for 20 knots before they were replaced with destroyer type machinery before her rebuilt into Ryuho. The other two Unspellables had 8 diesels producing 56,000 shp for a maximum speed of 29 knots, which was also replaced with destroyer machinery when they were converted into Soho and Zuiho.

I looked up the seaplane carriers as well. Chitose and Chiyoda were listed with steam turbine machinery producing 15,000 shp for 20 knots and Mizuho's steam turbines only produced 9,000 shp for a maximum speed of 17 knots.

The actual figures were diesels producing 15,200 shp for 22 knots on Mizuho and a combined steam and diesel plant (COSAD or CODAS?) producing 56,800 hp (44,000 shp and 12,800 bhp) for a maximum speed of 29 knots.

Therefore it looks as if the Japanese were (as usual) lying through their teeth about the characteristics of their warships and auxiliaries by saying the machinery of the seaplane tenders and submarine tenders had machinery that was considerably less powerful than it actually was.

Another thing I noticed that I did not know before was that at least the 3 submarine tenders were designed so that they could be converted into fast tankers as well as light fleet carriers.
 
As this is evolving into a better prepared Japan thread...

Point Of Departure 1931

Japanese Merchant Fleet

The British Official History on Merchant Shipping and the Demands of War, Japan had 1.7 million G.R.T. worth of merchant ships over 100 G.R.T. (4% of the world fleet) in 1913, which rose to 4.5 million (7% of the world fleet) by 1937. The same source said that in 1939 Japan had 47 tankers over 1,600 G.R.T with an aggregate displacement of 400,000 G.R.T out of a total merchant fleet of 1,054 ships over 1,600 G.R.T. with an aggregate displacement of 5 million tons.

Quote from the British official history on the War in the Far East
During the 1930s Japan had improved and enlarged her merchant fleet by replacing slow and out-of-date vessels with fast new ones. By 1940 the merchant fleet consisted of over 700 ocean going freighters, 132 passenger-cargo vessels, off which forty-nine were capable of speeds of 15 knots or over, and forty-nine ocean-going tankers. The total tonnage of this fleet on the outbreak of war in December 1941 was approximately six million and the percentage of imports carried in her own vessels had risen from fifty-four in 1937 to sixty-five in 1941. From 1937 onwards, having denounced the Washington Treaty on Naval Limitation, Japan began to strengthen her naval forces at the expense of merchant shipbuilding output, since even in this period steel supply was limited and naval yards could cope with only some 40% of the naval requirements the remainder having to be met by civilian shipyards.
To illustrate it there is a table, which shows that 1,713,985 tons of merchant ships were built 1937-41, declining from 442,382 tons in 1937 to 237,617 tons in 1941. 497,901 tons of warships were built over the same period, rising from 55,360 tons in 1937 to 225,159 tons in 1941.

The appendix on the Japanese Economy has other tables showing that their shipyards would go on to build 3,301,000 tons of merchant ships over 500 tons between 8th December 1941 to 15th August 1945, i.e.: 273,000 tons to the end of 1942; 769,000 tons in 1943; 1,699,000 tons in 1944; and 560,000 tons to 15th August 1945. If they had adequately protected the freighters bringing iron ore from the Southern Area, Japanese would have been able to double its steel output 1943-45. Although the increased total would still have been dwarfed by America's production, it would still have allowed a significant increase in the number of warships, auxiliaries and merchant vessels produced by Japan over 1943-45.

Ideally Japan should have built up its merchant fleet to at least 9 million tons and preferably 12 million tons between 1931 and 1941. Apart from making Japan better prepared for war, transporting all her imports in domestic bottoms instead of about 60% would have saved foreign currency which could have been be used to increase Japan's stockpiles of strategic raw materials. Japan probably didn't have the shipbuilding capacity to do it without cutting back on is output of warships and even IOTL the supply of steel 1937-41 was tight. However, they could have bought more new and second hand ships from abroad.

The British shipbuilding industry would have been glad of the work, because construction had declined from 1.5 million tons a year over 1928-30 to 190,000 tons in 1932, 137,000 tons in 1933 and then gradually climbed up to 972,000 tons in 1938, still well short of the pre Depression output. Furthermore Great Britain and Ireland had 3½ million tons of merchant ships laid up in 1932, while Japan only had 250,000 tons laid up, one fourteenth of the British total.

However, I don't know if the Japanese Government could afford to subsidise a 50% expansion of its merchant marine, even if it was spread over 10 years, especially in combination with the expansion of the Imperial Japanese Navy that I am going to propose. Therefore expansion of the Japanese merchant marine between 1931 and 1941 ITTL is limited to doubling of the tanker fleet to about 100 ocean going vessels in December 1941 and if Japanese shipyards don't have the capacity to build them they buy them abroad.

Changes To Imperial Japanese Navy Building Programmes 1931-42
1931 Fleet Replenishment Law

Taigei, built to an enlarged design displacing 15,000 tons, standard and propelled by 6 diesels producing 21,000 bhp for a maximum speed of at least 20 knots, but officially the maximum speed was less than that. The 50% increase in size was to allow her to be converted into a higher capacity fast tanker or an aircraft carrier capable of carrying 54 aircraft. (All compliments will be in units of 3 or 9 as Japanese naval air squadrons normally had 9 aircraft each.)

Instead of the 4 large torpedo boats of the Otoro class, which were built to exploit the 600 ton loophole in the First London Naval Treaty they built 8 Type A escorts of the Shimushu class to exploit the 2,000 ton loophole. The Japanese could have built something bigger, but it would also have been more expensive and I'm trying to minimise the increase in cost over the real world.

1934 Fleet Replenishment Law

Instead of the 16 Otori class that were ordered (8 built and 8 cancelled in favour of 8 submarine chasers) build 32 extra Type 8 escorts. All 32 ships were still ordered, but the Japanese also built 16 submarine chasers of about 300 tons instead of 8.

3 seaplane tenders and 2 submarine tenders built to an improved version of the enlarged Taigei design. Their displacements were 50% larger than the ships that were really built and their machinery was 50% more powerful also, i.e., increased from 8 diesels producing 56,000 bhp to 12 producing 84,000 shp.

1937 Fleet Replenishment Law

4 Shokaku class ordered by having 2 extra ships built in place of Yamato and Musashi. This also means the Japanese don't have to build the munitions transport Kashino. Some of the money saved would be required to pay for the aeroplanes for the carriers air groups and train the aircrew to operate them. However, a considerable amount of money, steel and shipyard resources should be saved, which was used to buy more escort vessels and auxiliaries.

20 Type A escorts were ordered instead of 4, which with the 40 ordered in earlier programmes gives Japan 60 ocean going escort vessels organised into 4 squadrons of 12 plus 12 spares. The Japanese could have built Matsu class destroyer escorts because the 105,000 ton destroyer quota was abolished at the end of 1936, but they would be more expensive and consumed more resources.

3 enlarged Nisshins instead of the real Nisshin and 2 Katori class training cruisers. In common with the earlier auxiliaries built under the shadow programme they were 50% larger in displacement and had machinery that was 50% more powerful.

IOTL the Japanese did not start to build new oilers to replace the ships built around the end of the First World War until the 1941 Supplementary Programme, 8 ships with similar characteristics to the civilian Type 1TL ships were built under the 1937 Law.

The Japanese Government still subsidised the construction of 2 large and 5 small liners in this period ITTL. However, only 2 of them incorporated features that would allow them to be converted to aircraft carriers, that is the large ones that became Hiyo and Junyo incorporated. The money saved was used to pay for other projects.

The United States reaction to Japan ordering of 4 aircraft carriers in 1937 instead of 2 was that the Navy Act of 1938 authorised the increase of the American aircraft carrier fleet from 135,000 tons to 215,000 tons rather than the increase of 40,000 tons authorised in the real world. The USN used this to order 2 Yorktowns (CV8 Hornet and CV8A Constellation) in FY1939 for completion in 1941 and 2 ships of a new design to be ordered in FY1940 and competed in 1943 (CV9 Essex and CV10 Yorktown II). The American battleship building programme was not changed.

1939 Fleet Replenishment Law, 1940 Supplementary Programme and 1941 Supplementary Programme

4 Shokaku class aircraft carriers ordered under the 1939 Law instead of Tahio, Shinano, No. 111 and Unryu. (IOTL Unryu wasn't ordered until the 1941 Supplementary Programme). More Shokaku class were ordered instead of Tahio class ships because they were cheaper, consumed less steel and should have been quicker to build. In the real world the Americans ordered 11 aircraft carriers (CV9-19) in their FY1940 programme and 2 more (CV20 and 21) in FY1941 for a total of 13. Therefore ITTL the Americans did not order any more aircraft carriers in response to the Japanese ordering 3 extra ships in 1939.

2 enlarged Nisshins instead of the 3rd Katori class training cruiser ordered under the real 1939 Law and the 4th Katori, which was ordered under the 1940 Supplementary programme. These were completed as aircraft carriers.

The number of escort vessels ordered under the 1941 Supplementary Programme was increased from 30 to 60 to form 4 squadrons of 12 with the rest as spares to cover refits and replace war losses.

12 oilers with similar characteristics to the Type 1TL were ordered under the 1939 Law, but none were ordered under the 1941 Law ITTL. These ships and the 8 ships ordered in 1937 were in addition to the 100 merchant tankers that the Japanese possessed in December 1941 ITTL.

1942 Fleet Replenishment Law

8 Tahio class and 9 enlarged Nisshin class in place of the one Yamato, 2 Super Yamatos, 2 battle cruisers, 2 Tahio class, one Unryu class, 3 seaplane tenders, 2 large submarine tenders and 4 training cruisers ordered under the real 1942 Law. However, they were all cancelled and replaced by 20 Unryu class in the Modified 1942 Law (instead of 5 Tahio and 15 Unryu class ordered in the real world) because they were easier and quicker to build. IOTL 6 of the 16 ships ordered were laid down and 3 completed by the end of 1944. ITTL the Japanese were able to lay down 12 ships and complete 6 by the end of 1944 out of 20 ordered.

The real 1942 Law included 4 escort vessels, which was increased to 34 in the Modified 1942 Law. However, none were ordered under either Law ITTL because the 60 ordered in the 1931 to 1937 Laws had been completed by the end of 1941 and 60 had been ordered in 1941. On the other hand the 42 Matsu class destroyer escorts ordered in the Modified 1942 Law were brought forward to the original version to replace and expand the force of old destroyers converted to patrol vessels.

Miscellaneous

IOTL the Japanese converted 12 destroyers to patrol vessels, which were equivalent to the British V&W class long range escort conversions, but ITTL they converted another 12 destroyers between 1931 and 1940 rather than scrapping them. Combined with the 60 escort vessels ordered between 1931 and 1937 the IJN had a convoy escort force of 84 vessels organised into 6 squadrons of 12 plus spares to cover refits. IOTL they actually had about 30 ships made up of the converted destroyers, 12 torpedo boats and the 4 escort vessels ordered in 1937. In the real world there were also the 30 escort vessels ordered in 1941, but none of them would complete until 1943. ITTL there were 60 on order, but none of them would complete until 1943 either.

IOTL the administrative side of the Japanese convoy escort force was more advanced too because the IJN had set up 2 commands to supervise convoys from Japan to the Japanese Pacific Mandates and French Indo-China (extended to Singapore in 1942) in 1940 instead of 1942. Furthermore as part of the ASW mobilisation they became part of the Grand Escort Fleet command set up in November 1941 instead of 2 years later. They also started to form the 901st Air Group of maritime reconnaissance aircraft 2 years earlier too, but they wouldn't receive ASV radar until 1943.

Summary

Between 1937 and 1941 the Japanese order 8 Shokaku class (4 completed by the end of 1941 and 4 completed in time for the Battle of the Philippine Sea) instead of 4 Yamato class battleships, 2 Shokaku class, Tahio and Unryu. They also complete 6 Unryu class by the end of 1944 instead of 3. The Americans only build one extra aircraft carrier in response (CV8A Constellation) because they embarked on a huge programme of naval expansion in 1940 anyway.

Between 1931 and 1941 the Japanese IOTL ordered 2 large liners, 5 smaller liners and 7 auxiliaries of about 10,000 tons that were designed to be converted to aircraft carriers, plus 4 slow cruisers of about 6,000 tons. ITTL the Japanese ordered 2 large liners, 11 auxiliaries of about 15,000 tons and 20 tankers that could be converted into aircraft carriers over the same period. The 4 extra auxiliaries were built in place of the 4 training cruisers. The 5 smaller liners, were still built, but without the features that would enable to conversion to aircraft carriers. The 11 large auxiliaries were built that were capable of being converted into aircraft carriers with air groups of 54-60 aircraft and a maximum speed of about 28 knots. The tanker conversions can only carry 12 aircraft and a maximum speed of 15 to 18.5 knots (depending on the source) but that was adequate as they weren't intended to operate with the fleet.

At the outbreak of the Pacific War IOTL the Japanese actually had 10 aircraft carriers in service consisting of 6 large ships (Akagi, Kaga, Hiryu, Soryu, Shokaku and Zuikaku), one light fleet carrier (Ryujo), one converted liner (Taiyo), one converted auxiliary (Zuiho) and the Hosho. Fitting out were another auxiliary conversion (Soho), 2 large liner conversion (Hiyo and Junyo) and one smaller liner conversion (Unyo) which would be completed in the first half of 1942. Another small liner conversion (Unyo) and another auxiliary conversion (Taigei into the Ryuho) would be completed in the second half of 1942.

ITTL the Japanese would have had 14 aircraft carriers consisting of 8 large ships (2 capital ship conversions, 2 Soryu class and 4 Shokaku class), one light fleet carrier (Ryujo), 2 converted auxiliaries (Zuiho and one ordered in 1939 instead of the training carrier Kashii), 2 tanker conversion (instead of the Unyo) and Hosho. Fitting out were another 2 auxiliary conversions (Zuiho and one ordered in 1939 instead of the training cruiser Kashihara), Hiyo and Junyo as IOTL and 2 more tanker conversions in place of Unyo, which would be completed in the first half of 1942. Another 2 tankers would be converted by the end of 1942 in place of Chuyo, but the only auxiliary conversion was Taigei into Ryuho as IOTL.

By contrast the Japanese had 5 large aircraft carriers (Lexington, Saratoga, Yorktown, Enterprise and Hornet) plus 2 smaller ships (Ranger and Wasp), but they only had one more aircraft carrier ITTL (Constellation an additional Yorktown class ship). 13 Essex class were on order, but the first would not be completed until the end of 1942. However, the Japanese might complete more cruisers into light fleet carriers.

The Japanese also doubled their aircrew training programme. Guy Robbins in the Aircraft Carrier Story 1908-45 wrote that in December 1941 the IJN had 3,500 pilots of whom about a third were carrier qualified, but I think it would have been more like 1,750 because he also wrote that the Japanese trained very few pilots during the 1920s and that even in the 1930s they trained as few as 100 a year, which wasn't enough to man all aircraft and establish an adequate reserve. However, 3,500 (of whom about 1,200 were carrier qualified) would have been enough to man all aircraft and establish an adequate reserve even though there were 735 aircraft aboard 13 aircraft carriers against 513 aircraft aboard 9 aircraft carriers (Hosho not counted ITTL or IOTL).
 
Most interesting read NOMISYRRUC, however i do have an observation. I'm sure the point has been made before, imo don't think it is realistic to have the japanese build only carriers and completely abandon building any new BBs, all other great powers were building new BBs. You can have a more air minded IJN top brass i guess which could result in Yamatos tailored more to accompany/support the CVs as well as serve with the battle line, being smaller and faster. As for the training cruisers (and indeed the other ATL ships), unless this ATL provides for increased slip size in the shipyards they were built, can't have anything much longer than a Katori built on those slips (have to check which shipyards/slips, but they must be quite small, maybe 150m ones).

Btw regarding the MACs or smaller, slower (and much chearer than the 'Yos) CVEs more comparable to the US ones that we discussed previously, i was looking at some of these (just the bigger, faster ones could easily provide a dozen hulls) as perfect candidates for such conversions:

http://www.navypedia.org/ships/japan/jap_aux_aux_cr.htm
http://www.navypedia.org/ships/japan/jap_aux_aux_scv.htm

Btw, i suspect that the very small aircraft capacity of the japanese MAC conversions was because they still retained most of their cargo carrying capacity. I'm also reading that the larger, faster ones (the Shimanes) were for IJN, while the slower Yamashios with no hangar at all afaik were for IJA. I would see no reason why any of these or the vessels in the links above cannot carry about two dozen planes if converted to full CVEs.
 
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Had another look at the slips, it appears that indeed probably all tenders and seaplane carriers CAN be built 50% bigger, however doing so will bump accordingly (being bigger it might take a bit longer to build) other ships that followed them on the respective slips, especially CVs.

As for the Katori slips, it appears the the largest Yokohama slip was 200m, and until further info, i assume two of the Katoris were laid on it, the other two being build on the smaller 150m slip.

On that 200m slip they can build either an Agano type CL or CL-AA, or an OTL size Nisshin/Chitose type tender/CVL, but a 50% larger such tender will likely be longer than 200m, so it won't fit.
 
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trurle

Banned
Strategy is the successful comparison of apples to oranges. Which is more valuable? Speed, mass, or ability to take damage? I'd propose a formula something like this -

Aircraft carried * speed + tonnage / 100.

Junyo = 54*25+25000/100 = 1600
Unryu = 57*34+18000/100 = 2118
Zuiho = 30*28 + 12000/100 = 960

For defensive missions speed would not be as important. So for offense an Unryu might be worth 1.3 Junyos, for defense they're about even.
Such FOM (figures of merit) is always a simplification. But to do it seriously (for defence) the FOM=(covered_area*firepower*time_before_destroyed)^(1/3)
covered_area=speed*speed
firepower=aircraft
time_before_destroyed=tonnage

therefore, more realistic equation of combat FOM (normalized for 1600 for Jyuno):
Junyo = 1.693*(25*25*54*25000)^(1/3)=1600
Unryu = 1.693*(34*34*57*18000)^(1/3)=1793
Zuiho = 1.693*(28*28*30*12000)^(1/3) = 1111

Difference between models in my FOM is less pronounced compared to Glenn239 version. Unryu and Zuiho are therefore very close in "bang per buck" (utility divided by cost). Of course, all of this calculation is nonsense. Threshold factors like torpedo protection bulge efficiency (penetrated or not?) or details of construction of compartmentalization and ventilation system (which killed Taiho carrier) may make any of 3 listed classes vastly superior or inferior to others. The devil is in the details.
 
Most interesting read NOMISYRRUC, however I do have an observation. I'm sure the point has been made before, imo don't think it is realistic to have the japanese build only carriers and completely abandon building any new BBs, all other great powers were building new BBs. You can have a more air minded IJN top brass i guess which could result in Yamatos tailored more to accompany/support the CVs as well as serve with the battle line, being smaller and faster.
I'm not sure that it's realistic for Japan to build more aircraft carriers instead of the Yamatos either. However, I have read that Yamamoto and his faction was pressing for the construction of more aircraft carriers in place of the Yamato class, which is why I put it in.
As for the training cruisers (and indeed the other ATL ships), unless this ATL provides for increased slip size in the shipyards they were built, can't have anything much longer than a Katori built on those slips (have to check which shipyards/slips, but they must be quite small, maybe 150m ones).
I thought that might be a problem. It would have been a good thing in itself if the Japanese had built more long slipways and/or extended some of the existing ones between 1931 and 1936, but it would also have cost more and I don't want this thread to evolve into a Japan wank.

Therefore the 7 auxiliaries built IOTL would be built to the OTL designs and if it was not possible to build 4 Nisshin class in place of the 4 Katori class then don't built anything at all. The money and shipyard resources thus saved would be spent on the extra tankers and escort vessels built under the 1939-41 Programmes.

Btw regarding the MACs or smaller, slower (and much chearer than the 'Yos) CVEs more comparable to the US ones that we discussed previously, i was looking at some of these (just the bigger, faster ones could easily provide a dozen hulls) as perfect candidates for such conversions:

http://www.navypedia.org/ships/japan/jap_aux_aux_cr.htm
http://www.navypedia.org/ships/japan/jap_aux_aux_scv.htm

Btw, i suspect that the very small aircraft capacity of the japanese MAC conversions was because they still retained most of their cargo carrying capacity. I'm also reading that the larger, faster ones (the Shimanes) were for IJN, while the slower Yamashios with no hangar at all afaik were for IJA. I would see no reason why any of these or the vessels in the links above cannot carry about two dozen planes if converted to full CVEs.

I haven't followed the link, but I think they could have carried 27 aircraft (3 squadrons of 9) while retaining their cargo carrying capacity. That would have been useful because the main job ITTL would be to escort convoys on the routes from the Southern Area to Japan and from Japan to Truk. Therefore the Japanese could have provided the convoys with better protection without reducing their capacity to transport oil and as a bonus the tanker based aircraft carriers could also refuel the escort vessels.
 
Regarding the MACs, imo probably they could not carry cargo if they will be fully converted to CVEs, as the hangars for at least 24 aircraft will presumably occupy most if not all the former cargo holds etc.

As for the Katoris, like i said any other warship instead of them is better, they could for instance start building Aganos (that were delayed OTL because there was no slips available) on the 200m slip, and build couple of darn Katoris on the 150m one if they really want them that badly. I think the 200m one could probably fit an Oyodo as well, which could mean either they finish both Oyodos, or some other ships from the 1939 or 1941 programes get laid down earlier than OTL (Oyodo itself was built on a slip that could take an Unryu Class CV).

Finally, wonder how realistic would be for Yamamoto to just stomp his feet in 1940 and obtain at least cancelling Yamato-class no.111 or at the latest, order it scrapped immediately when construction stops in late 1941, thus making the slip available for another warship in mid-1942 (another Unryu class if Midway still happens). But it is confusing what one can read about Yamamoto and IJN in general, on one hand he is said to be very airminded, on the other hand things like Midway are given as showing that they (he?) still saw the BBs as the main force of the fleet. You can't have both, either he was airminded or not. If he was really air minded pobably what happend at Midway could be explained as simply just giving the BBs something to do to keep morale high and all that (like King/Pye wanted to do in the USN), though the cost in fuel absolutely was not worth it. But at Guadalcanal he didn't hurled every available BB at the americans as soon as practicable to really given them something to do (and potentially useful at that - yes i know about the oiler/fuel limitations and maybe they can't send all 11 BBs like at Midway, but say half of them surely, imagine the airfield being bombarded by half a dozen BBs earlier in the campaign or even same time as OTL), so it's all quite puzzling.

But i considerably digress.
 
Anyway, there can be lots of permutations on this subject (IJN slips/shipbuilding etc.) for fun here's my idea of some rough shipbuilding timeline to get a better IJN.

-When building Ryujo cheat a bit more and make it as large as necessary to carry the designed number of aircraft effectively (48 but even more would not hurt either). Will still be a CVL but more like Ranger and probably slower at say 28kt but would be a more useful ship.
-finish Akagi's modernization, fit 12 and preferably 16 Type 89 12,7cm AA guns etc.
-order another Hiryu class instead of Junyo and another Shokaku or Taiho (preferably with 16 Type 98 10cm AA guns instead of 12) instead of Hiyo.
-cancel Yamato-class no.111 and build another Taiho, and finish Shinano resources permitting either as full BB or just BB-XCV in 1944 - even that is better than nothing.
-when the shadow carrier program is activated convert all the available auxiliaries first (if they are slightly larger and have two level hangars like Ryujo would help of course, as a trade-off they can be fewer, say six), finish Nisshin as a CV not tender in 1941/early 1942, then convert Chitose and Chiyoda etc.
- if still want to convert liners, as the 21kt Taiyo is so slow and ineficient for size, either fit it and it's sisters with destroyer turbines for 23 or so kts (perhaps) and just about able to work with the 24kt slow BBs, or don't convert any more liners afterwards and proceed to convert almost similar speed (18-21kt) AMCs or auxiliary seaplane tenders to CVEs, convert as many as possible in 1943-44 for mainly ASW roles, to be followed by as many 1TL and 2TL carrier or MAC conversions as possible.
-as no/fewer Katoris are built the thus made available 200m slip can build Aganos and/or Oyodos, thus freeing a slip to lay down Unryu itself from the emergency program of 1941 earlier than otherwise possible.
-If Midway still happens plan to convert Ibuki immediately to CVL; should be ready in early part of 1944.
-Unryu type CVs ordered after a debacle at Midway must be simplified as much as possible and fitted with two shaft half-cruiser machinery for 28-29kt with 76-80,000HP but retaining aircraft capacity, let's call it the Amagi class; hopefully the building time can be reduced to 18 months and maybe 6 could become available in 1944.
 
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Did the Taiyo class carriers have arresting gear or not?

Most sources say no.

Despite what can one read in old sources, reputable researchers indeed show that the Taiyos and the other CVEs had arresting gear, how would it be otherwise anyway, they didn't convert them to carriers with two elevators and able to hold about 30 aircraft split between A6Ms and B5Ns and intended to support the fleet without being able to land the planes!
 
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