WI: Japanese before WWII decided to build auxiliary carriers instead of auxiliary cruisers?

trurle

Banned
IOTL, Japan built (or converted) both auxiliary carriers and auxiliary cruisers. With skew to auxiliary cruisers.
https://en.wikipedia.org/wiki/List_of_Japanese_auxiliary_cruiser_commerce_raiders

After all, cruiser conversion was much cheaper compared to carrier conversion, and combat efficiency of both conversion was dubious.
Auxuliary carrier Akitsu Maru was the only one of sort.
https://en.wikipedia.org/wiki/Japanese_aircraft_carrier_Akitsu_Maru

Therefore, the questions:
1) Could you imagine sequence of events leading to much more Japanese auxiliary carriers?
2) What will be change of Japanese strategy and tactics if several more (say 10) auxiliary carriers are available in WWII? Please focus on strategy/tactics rather than changes of course of war (the changes would be small anyway).
 
The questions:
1) Could you imagine sequence of events leading to much more Japanese auxiliary carriers?
2) What will be change of Japanese strategy and tactics if several more (say 10) auxiliary carriers are available in WWII? Please focus on strategy/tactics rather than changes of course of war (the changes would be small anyway).
I would posit 10 Tankers converted to Oilers/aircraft ferry ships. If you had crated aircraft stored below the flight deck, and assembled aircraft upon the flight deck, you could get quite a nice improvement to the IJN/IJA aircraft deployments in far away places, and there would be no talk about the range of such ships.
 

trurle

Banned
I would posit 10 Tankers converted to Oilers/aircraft ferry ships. If you had crated aircraft stored below the flight deck, and assembled aircraft upon the flight deck, you could get quite a nice improvement to the IJN/IJA aircraft deployments in far away places, and there would be no talk about the range of such ships.
Sounds interesting. It would become hybrid of Hayasui class with Akitsu Maru.
https://en.wikipedia.org/wiki/Japanese_fleet_oiler_Hayasui
 
Sounds interesting. It would become hybrid of Hayasui class with Akitsu Maru.
https://en.wikipedia.org/wiki/Japanese_fleet_oiler_Hayasui
I like that!

You asked about tactics, and I would guess it would depend on exactly when the IJN/IJA wanted to start these conversions, how long they took, and thus when the ships become operational. Pre-war would be ideal, but don't think that is going to happen.

On the design, get your lightweight (You will not be having to build to withstand landings, after all, so 'just strong enough to bear the weight load' is all you need) FD up high, and just stack crated aircraft up in the storage space below. Fill FD with assembled aircraft, fly them off, then use multiple, deck edge 'freight elevators' to bring crates up to the FD. If you design a set of heavy, waterproof, blackout tenting to be quickly raised up and around the FD, you can provide your assembly workers a dry, warm, well-lit workplace within which to get the next set of aircraft unpacked and assembled. Rinse and repeat.

Combining storage of crated aircraft with a flying off deck/assembly area, should give quite a bit more capacity to any single ship of this type, and perhaps one ship could ferry aircraft to multiple, widely separated islands, using the travel time between to ready the next batch to be flown off when you reach the distance you plan to launch them from. I don't have a clue about the ratio of crated/assembled aircraft storage space requirements, but perhaps a 4:1 is not unreasonable? 30 on deck would give 120 in crates if that is the case, so one of these might be able to deliver 4-5 times what an OTL Akitsu Maru could, if you don't mind starting off with a FD full of assembled planes, and a storage deck packed full of crated planes.
 

trurle

Banned
I like that!

You asked about tactics, and I would guess it would depend on exactly when the IJN/IJA wanted to start these conversions, how long they took, and thus when the ships become operational. Pre-war would be ideal, but don't think that is going to happen.

On the design, get your lightweight (You will not be having to build to withstand landings, after all, so 'just strong enough to bear the weight load' is all you need) FD up high, and just stack crated aircraft up in the storage space below. Fill FD with assembled aircraft, fly them off, then use multiple, deck edge 'freight elevators' to bring crates up to the FD. If you design a set of heavy, waterproof, blackout tenting to be quickly raised up and around the FD, you can provide your assembly workers a dry, warm, well-lit workplace within which to get the next set of aircraft unpacked and assembled. Rinse and repeat.

Combining storage of crated aircraft with a flying off deck/assembly area, should give quite a bit more capacity to any single ship of this type, and perhaps one ship could ferry aircraft to multiple, widely separated islands, using the travel time between to ready the next batch to be flown off when you reach the distance you plan to launch them from. I don't have a clue about the ratio of crated/assembled aircraft storage space requirements, but perhaps a 4:1 is not unreasonable? 30 on deck would give 120 in crates if that is the case, so one of these might be able to deliver 4-5 times what an OTL Akitsu Maru could, if you don't mind starting off with a FD full of assembled planes, and a storage deck packed full of crated planes.
The assembled aircraft enclosing box volume vs crated parts volume depends on the level of assembly. Typical compromise solution was to have propeller blades, cockpit panels, wings, radiators, tail plane and stabilizers all assembled to level to be either tied along halves of fuselage or tucked inside it. Typical fast-assembly fighter crates would be 2 crates 2x2x5 meters each, giving volume advantage of 5.5:1 (or 3:1 if aircraft with foldable wingtips is used).
Regarding the idea of tents and on-ship assembly, it seems attractive but likely has only niche applications. A lot of aircraft would be damaged during parts mating in rolling seas conditions, and habitability of tents will be very poor.

Some improvements are possible though. Crates walls can be reused to create a semi-rigid assembly hangar on top deck. Wooden walls will give more thermal isolation and provide some protection against wave washout. After assembly is complete, the walls can be dumped aboard or stored below flight deck. Gimbal-stabilized cranes can be used to mate large parts (like wings of halves of fuselage).

Main show stopper for such a factory-ship may actually be a lack of technicians. Would need to ferry technicians on flying boats from ship to ship, depending on need. That overhead may lead to decision to just take trip a little longer and then to unload crates in port. At least if port do exist and environment is safe.
 
I like the idea above. My thought would be to use the auxiliary carriers as the ground attack support for hostile landings. This would (should) free up the fleet carriers for exclusive use for fleet engagements.
 
I like the idea above. My thought would be to use the auxiliary carriers as the ground attack support for hostile landings. This would (should) free up the fleet carriers for exclusive use for fleet engagements.
That and make moving land based aircraft forward as easy and quick as possible, as you wouldn't need to have a string of airbases from which to stage them from. However, the ships above are not carriers in and of themselves, but merely transports that can fly off aircraft, not recover them and rearm them. For that you would need actual CVE's or CVL's, which would be more capable, but would take longer to convert.
 
The assembled aircraft enclosing box volume vs crated parts volume depends on the level of assembly. Typical compromise solution was to have propeller blades, cockpit panels, wings, radiators, tail plane and stabilizers all assembled to level to be either tied along halves of fuselage or tucked inside it. Typical fast-assembly fighter crates would be 2 crates 2x2x5 meters each, giving volume advantage of 5.5:1 (or 3:1 if aircraft with foldable wingtips is used).
Sweet. I didn't know that, so I have just learned some additional interesting facts. Thanks.

Regarding the idea of tents and on-ship assembly, it seems attractive but likely has only niche applications. A lot of aircraft would be damaged during parts mating in rolling seas conditions, and habitability of tents will be very poor.
Ever see the curtains in hospitals, where they hang from a curved rod, and you just pull them around? I'm picturing something like sails of old (although definitely not white), but now instead of a vertical mast, they are 'run up' within a steel framework, forming a tunnel of sorts, and secured tightly on both sides of the flightdeck. Now run the second layer on the outside of the steel framework, and secure it likewise. So you end up with an enclosed, dry, well lit workspace in any but very heavy weather, in which case, you cannot really assemble the aircraft anyway, right?

Main show stopper for such a factory-ship may actually be a lack of technicians. Would need to ferry technicians on flying boats from ship to ship, depending on need. That overhead may lead to decision to just take trip a little longer and then to unload crates in port. At least if port do exist and environment is safe.
Why not have them flown ashore after assembly of the last planes? Seems likely that if your staging aircraft into a new base, your going to be needing ground crews, and why not fly them in in the seaplanes when the job is done. Workers would have to be trained to be able to assemble aircraft while afloat, true enough, but this is true whether or not they are IJN or IJA types, right?

I think you have asked a really interesting question here, and looking forward to what folks come up with!
 

trurle

Banned
Ever see the curtains in hospitals, where they hang from a curved rod, and you just pull them around? I'm picturing something like sails of old (although definitely not white), but now instead of a vertical mast, they are 'run up' within a steel framework, forming a tunnel of sorts, and secured tightly on both sides of the flightdeck. Now run the second layer on the outside of the steel framework, and secure it likewise. So you end up with an enclosed, dry, well lit workspace in any but very heavy weather, in which case, you cannot really assemble the aircraft anyway, right?
It resembles heavy-duty curtains some transport companies nowadays use to protect loading/unloading areas from elements. Also these are used in cheap clean rooms to keep away dirt. My experience with these curtains was what curtains are better than nothing, but but can still fail easily and junctions leak too much air plus thermal insulation is non-existent, therefore strong heaters/aircon/fans are necessary to maintain controlled environment. In 194x, ships has very weak electrical power networks, so environmental control of large tented hangar is going to be problematic.
Why not have them flown ashore after assembly of the last planes? Seems likely that if your staging aircraft into a new base, your going to be needing ground crews, and why not fly them in in the seaplanes when the job is done. Workers would have to be trained to be able to assemble aircraft while afloat, true enough, but this is true whether or not they are IJN or IJA types, right?
I thought about strategy to use assembled planes to transfer technicians, but feel such arrangement is over-complication. Factory-ferry vessel can assembly only small seaplanes with a limited crew capacity (likely max. 4 passengers per seaplane). Will need multiple shuttle flights to transfer hundreds of ground crew. Not impossible, but transfer is going to be very slow, eating away any potential time advantage. Using combination of rendezvous with long-range heavy seaplanes (like a couple of H6K2-L fabricated IOTL) with motor boats may offer faster solution for the ground crews transfer.
 
I would posit 10 Tankers converted to Oilers/aircraft ferry ships. If you had crated aircraft stored below the flight deck, and assembled aircraft upon the flight deck, you could get quite a nice improvement to the IJN/IJA aircraft deployments in far away places, and there would be no talk about the range of such ships.

Converting oil tankers runs up against the short numbers Japan posessed. 60 to 80 in 1941, depending on how they are counted. Japan went to war with a merchant and military cargo fleet roughly half that needed for full commercial and military traffic.
 
The real need for Japan from the 1930 - 1941 period should have been increasing their merchant marine capacity by 15 - 20%. Not having enough bottoms, not having a rational plan to move products and raw materials in their new empire, and lack of a coordinated ASW plan is what doomed (or greatly shortened) their ability to effectively battle the allies. Sorry trurle for sidetracking your thread.
 
I wonder why people still focus on more flightdecks for the IJN before WW2. Carriers were not the main issue here, as Japan already had more than anyone else. Problem was to get enough trained aviators on them as well as aircraft, which were always in short supply. It should be noted no carrier ever in the IJN carried its maximum load in both peace and wartime. Simply said, there were already more flightdecks available than there were pilots and aircraft to use them.

In wartime the Japanese did historically build a number of new aircraft carriers, but only a few got their assigned airgroups, due to shortages in both aircraft adn pilots. None of the Unryu class CV's of 1944 got a full airgroup and even Taiho had to do with fewer than normal aircraft (53 out of a capacity of 84), while both Shokaku and Zuikaku had a simmilar capacity of 84+ and never carried more than 74. This was all a result of the limmited flighttrainingcapacity of the IJN, where too few recruits were trained at a time, besides the typial Japanese shortage in aircraft engine production.
 
The real need for Japan from the 1930 - 1941 period should have been increasing their merchant marine capacity by 15 - 20%. Not having enough bottoms, not having a rational plan to move products and raw materials in their new empire, and lack of a coordinated ASW plan is what doomed (or greatly shortened) their ability to effectively battle the allies. Sorry trurle for sidetracking your thread.

I'm not sure when it was conceived, but by the end of 1941 there was a crash program underway to expand the cargo fleet by 100 percent. Steel had been stockpiled for this as well as copper & other mtls. The war emergency allowed deficient spending to cover construction costs. Fleet expansion was desired in the 1930s but tax revenue, credit limits, an fiscal sense prevented a rapid construction.
 

trurle

Banned
I wonder why people still focus on more flightdecks for the IJN before WW2. Carriers were not the main issue here, as Japan already had more than anyone else. Problem was to get enough trained aviators on them as well as aircraft, which were always in short supply. It should be noted no carrier ever in the IJN carried its maximum load in both peace and wartime. Simply said, there were already more flightdecks available than there were pilots and aircraft to use them.

In wartime the Japanese did historically build a number of new aircraft carriers, but only a few got their assigned airgroups, due to shortages in both aircraft adn pilots. None of the Unryu class CV's of 1944 got a full airgroup and even Taiho had to do with fewer than normal aircraft (53 out of a capacity of 84), while both Shokaku and Zuikaku had a simmilar capacity of 84+ and never carried more than 74. This was all a result of the limmited flighttrainingcapacity of the IJN, where too few recruits were trained at a time, besides the typial Japanese shortage in aircraft engine production.
I would disagree with statement "Japan has too much flightdecks". Ground losses of aircraft in Guadalcanal campaign (with many aircraft lost even while in crates) clearly indicate the insufficient aircraft carrying or assembly capacity. The point of crew training is less relevant to auxiliary carriers because these do not carry normal airgroups. The training requirements may be close to land-based aviation because only takeoff from auxiliary carrier will be practiced. Landing will be elsewhere.
 
I would disagree with statement "Japan has too much flightdecks". Ground losses of aircraft in Guadalcanal campaign (with many aircraft lost even while in crates) clearly indicate the insufficient aircraft carrying or assembly capacity. The point of crew training is less relevant to auxiliary carriers because these do not carry normal airgroups. The training requirements may be close to land-based aviation because only takeoff from auxiliary carrier will be practiced. Landing will be elsewhere.

What is the purpose of additional flightdecks when there are no aircraft, with aviators to use them?

My point was the IJN had a larger number of flightdecks already in the OTL. Adding more would not help them at all, as long as the increase in numbers of both aircraft and aviators did not go parrallel with it. It is the very same as creating more guns, but not the ammunition for it. It simply is a waist of resources to do so then, which in Japan already were in short supply and heavy demand.
 

trurle

Banned
What is the purpose of additional flightdecks when there are no aircraft, with aviators to use them?

My point was the IJN had a larger number of flightdecks already in the OTL. Adding more would not help them at all, as long as the increase in numbers of both aircraft and aviators did not go parrallel with it. It is the very same as creating more guns, but not the ammunition for it. It simply is a waist of resources to do so then, which in Japan already were in short supply and heavy demand.
Japanese historically has acute shortage of both replacement pilots and ammunition, especially ammunition for heavy and automatic weapons. This problem can be traced to the pre-war planning assuming the all-out war will continue for no longer than 6 months. Therefore, it made some sense for Japanese to maximize firepower, even to the detriment of endurance. Would additional auxiliary carriers be built pre-war, pilots will be assigned to them, although likely would be no replacement pilots, same as IOTL. Argument about lack of aircraft is incorrect. Japanese has to the very end a surplus of aircraft (10,000+ aircraft at moment of surrender), just these (older) aircraft were difficult to use in the environment of total Allied air superiority. In case of environment with more parity, Japanese obsolete aircraft can be still used, at least for recon and for ground attack roles.
 
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