Japanese logistics, purchase programs and war booty, reality and alternatives 1936-44

[tomo pauk]

The uphill battle for the Japanese aero industry:

 

[z42]

The uphill battle for the Japanese aero industry:

View attachment 816087

Interesting. Also tells something about the productivity of the American industry. If I'm reading the chart correctly, with about twice the manpower they're producing 10 times more (pounds of) aircraft. Or looking at the production per employee, goes from about a factor of 3 better in 1941 to a factor of 5 in 1944 (1945 productivity crashes for the Japanese, probably due to them being bombed and blockaded?).

 

[EwenS]

They also were not (usually) designed for deep diving. They could not use the 3rd dimension very well.

They dived about as deep as British and US subs of the era.

Most British subs from the late 1920s had a test depth of 300ft. The U class was 200ft but increased in later ships to 300ft but they were designed for use in shallower waters anyway. The T class saw it increased to 350ft by using thicker plate for the pressure hull and more welding in later wartime boats. The RN went to 500ft with the A class designed in 1942/43, which was just entering service as the war ended.

Pre-war the USN went from 200ft with the S class of 1918 to 250ft for most of its inter-war classes. The Gato class (completed from Dec 1941) was 300ft, increased to 400ft in the succeeding Balao class (from Feb 1943) and Tench classes. That increase was achieved by using thicker pressure hull plates and high strength steels. It was later increased to 450ft when more powerful pumps able to operate at increased depths became available late in WW2.

Japanese submarines inter-war went from 200ft for most of the 1920s to 250ft in the early 1930s to 330ft in the late 1930s and wartime boats.

The above are the test or operational diving depths. Usually submarines, at least those for the RN, were tested on trials to about 10% greater. Crush depth was usually taken to be about double the test depth. But at the time but the mathematical formulae required to accurately predict failure depthsand the various stresses, had to await computers in the post WW2 era. Subsequently a lot of the ideas about the stresses on a sub pressure hull shape of this era proved to be inaccurate.

It was the Germans who attained significantly greater diving depths. At the start of WW2 Type VII & IX were good down to 220-230m (722-755ft) with later Type VII boats able to go to 250m (820ft) or even 270m (886ft). Britain got a close look at the construction of a Type VII when U-570 was captured in Aug 1941. Sir Stanley Goodall, the DNC at the time, could not see why she had so thick a pressure hull and such flimsy frames. That started a reassessment of just how a submarine pressure hull should be designed. What is not clear to me is whether the Germans had a better understanding or simply arrived at it by chance. It also forced a reassessment of the necessary settings on depth charges to ensure that they could explode that deep.

 

[Shortround6]

They dived about as deep as British and US subs of the era.

Thank you for the correction/explanation.

 

[tomo pauk]

More advanced superchargers were the area where the Japanese lagged vs. the US and UK a lot. Bar engines' and aircraft prototypes, there were no 2-stage S/Cs in service, not the turboed engines. Making the good turboes required some fancy metalurgy, but the 2-stage superchargers did not. There was also less of the required 'plumbing' associated with the 2-stage engines. What was required is that it dawns on the people in charge of engine development. They can draw comparisons with the interwar run-on-the-mill engines with 1-stage S/Cs, and their 2-stage siblings that were being made for altitude record attempts, and then act accordingly.

 

[Shortround6]

Japanese seemed to do pretty well with their two speed single stage engines.
The Japanese were running into a limit with fuel. Which they were getting around with water injection. They hadn't resorted to intercoolers yet but that seems to be the only thing they had left to try.
The Mitsubishi Kinsei and the Nakajima Ha-109 seemed to do fairly well for a single stage engine. If you want power in the mid 20s and higher you need a lot of boost in the system and that means a lot of heat in the mixture and unless you can bring that heat down somehow, you don't get as much power from the two stage superchargers, even with high octane gas.
The P-63 is the poster child for this situation.
Yes they got another 10,000ft of altitude over the single stage engine in the P-39. But they were running 50in of boost to get it. Which is about 510mm of boost the way the Japanese measured it? Even with water injection the Japanese were topping out at around 350mm in their radials? But that was at the levels of heat they were getting with the single stage engines. Two stage superchargers are more efficient and don't heat the air quite as bad but you are not looking for 20-50mm. You are looking for a lot more and/or higher up.
The Japanese have to decide if they are going to use both intercoolers and water injection in order to make up for the low octane fuel. (The US used both on the R-2800 and had high octane fuel).
Or use the German method and use a large displacement engine that can make the desired power at altitude without using a two stage supercharger.

 

[tomo pauk]

Japanese seemed to do pretty well with their two speed single stage engines.

When dealing with the Allied aircraft powered by the 1-stage engines - yes, as well as against the F4F.
When dealing with 2-stage supercharged engines - no.

The Japanese were running into a limit with fuel. Which they were getting around with water injection. They hadn't resorted to intercoolers yet but that seems to be the only thing they had left to try.
The Mitsubishi Kinsei and the Nakajima Ha-109 seemed to do fairly well for a single stage engine. If you want power in the mid 20s and higher you need a lot of boost in the system and that means a lot of heat in the mixture and unless you can bring that heat down somehow, you don't get as much power from the two stage superchargers, even with high octane gas.

These two engines were in ballpark with the DB 605A or the BMW 801C, the Ha 109 being a bit better than the Kinsei at higher altitudes, and Kinsei 60 series with water-alc injection being better down low. Ha 109 never gotten the proper exhausts and w-a injection certainly robbed performance of the aircraft the 109 powered.
We know from the European air war that neither 605A nor the BMW 801C (nor D) will not cut it above 20000 ft vs. the better fighters of 1944/45. There also was no advanced aerodynamics on the Japanese fighters to help out. So the engines will need to do the heavy lifting.
Japanese knew about the intercoolers by the mid-1930s, as did the rest of the world.
They can also keep the compression ratio under 7:1, even better if it is under 6.5:1.

The P-63 is the poster child for this situation.
Yes they got another 10,000ft of altitude over the single stage engine in the P-39. But they were running 50in of boost to get it. Which is about 510mm of boost the way the Japanese measured it? Even with water injection the Japanese were topping out at around 350mm in their radials? But that was at the levels of heat they were getting with the single stage engines. Two stage superchargers are more efficient and don't heat the air quite as bad but you are not looking for 20-50mm. You are looking for a lot more and/or higher up.

Adding 10000 ft to one's rated altitude is a major thing.
The big Japanese engines will require lower boost than what the V-1710 or the Merlin required. With w-a injection, the Japanese radials topped at 1260mm Hg (= 49.6in for the Kinsei 60 series on the Ki-46-III per Sovier tests, or +500 mm Hg; same for the Homare per the Allied test reports), or +450 mm Hg for the Kasei 20 series on the G4M.

Or use the German method and use a large displacement engine that can make the desired power at altitude without using a two stage supercharger.

German 'method' - you probably have the DB 605AS and D family in the mind?
These engines powered the small and trim fighters, that were the Bf 109G-10 and K4 and the like. Japanese fighters (bar the Ki-44) were much bigger than the 109, and we have a thing of the DB engines being V12s, that helps with streamlining. German 2-stage supercharged engines - a small number of them made - were offering far better altitude power than even their best 1-stage supercharged siblings.
My point - Japanese will need a much more capable engine than the 605AS or D. Especially since they will be in the ever greater numerical disparity, and their lack of fuel will hurt the influx and ability of the new pilots.

 

[tomo pauk]

Some alternative IJA fighters:
- Ki 60, but powered by a good radial (say, Kinsei) from 1942 on - Ki 60 was with a smaller wing than the Ki-61, but the -61 was with a more refined cooling system that was less draggy, so even though the wing was bigger, the total drag remained the same
- Ki-44 with the better exhausts and water-alc injection
- Ki-44 with the Homare as a fighter tailored for the very high speed
- Ki-44 with the water-alc Ha 115-II (Sakae family), manufactured instead of the later Ki-43s
- definitely axe the Ki-45 as a fighter; even the Ki-60 with the 2-speed Ha 102 engine will bring more to the table, and can be produced almost two for each Ki-45 not produced (talk another 1500 fighters)
- take note of the Ha 42 engine, making a fighter around that engine might've been a good move
- don't fiddle with the Ki-43 - manufacture it as-is early on, and introduce the changes, like the butterfly flaps later, but don't forget the protection for the pilot and fuel (thus the Ki-27 can be phased out earlier)

Obviously, if the more advanced supercharges can be had for the respective engines, even better. As you can see, I avoid as a plague the two-engined fighters for Japan.

 

[tomo pauk]

Foreign stuff worth taking a deeper look:
- radars, RWR, chaff
- engines with 2-stage superchargers, already from the mid-1930s
- Fw 190, He 100, He 111, Ju 88 (the two bombers mostly due to their bomb/torpedo load), Ju 87 (also for it's bomb load)
- Me 109, mostly for the ease of construction, but also for it's good performance
- MC.202, Ro.58 (but for the fast bomber task)
- Mosquito definitely
- Catalina, DB-7, P-51
- Mine shell, adiabatic fuses, MK 108 (mostly for it's RoF, and the cheap and easy construction method), 23mm Madsen - both idea and execution

 

[Reluctant Poster]

I'm skeptical of blimps. They probably disappeared for a reason. Steal the Allied ASW playbook and build more of the H8K's, and then build escort carriers and equip them with some bombers obsolete for front-line service?

They don't need escort carriers. They are not crossing the Atlantic. Most of their important shipping lanes are close enough to land to use shore based aircraft. Its far easier to enslave the local population to build an airstrip than to build an escort carrier
Here is interesting discussion of Japans convoys or lack there of.

Japanese Convoy Routes 1943-1945

Japanese Convoy Routes 1943-1945

www.academia.edu

 

[EwenS]

Foreign stuff worth taking a deeper look:
- radars, RWR, chaff
- engines with 2-stage superchargers, already from the mid-1930s
- Fw 190, He 100, He 111, Ju 88 (the two bombers mostly due to their bomb/torpedo load), Ju 87 (also for it's bomb load)
- Me 109, mostly for the ease of construction, but also for it's good performance
- MC.202, Ro.58 (but for the fast bomber task)
- Mosquito definitely
- Catalina, DB-7, P-51
- Mine shell, adiabatic fuses, MK 108 (mostly for it's RoF, and the cheap and easy construction method), 23mm Madsen - both idea and execution

At the end of WW2 there was a US Naval Technical Mission visited Japan and before 1945 was out produced a long series of reports on a variety of matters, including radar, which are now available on the internet. This is the list:-

HyperWar: U.S. Naval Technical Mission to Japan

U.S. Naval Technical Mission to Japan: The post-war investigation of Japanese technology and methods.

www.ibiblio.org

Copy & paste each title into your browser and you should find them in the Fischer-Tropsch Archive. This is just the first 3 on Japanese radars.

Also a recent thread here (the tables attached at the end seem to be terribly confused in some of the figures they present)

NavWeaps Forums-Japanese Naval Radar.

Japanese Naval Radar. Neil.

www.tapatalk.com

 

[Reluctant Poster]

They don't need escort carriers. They are not crossing the Atlantic. Most of their important shipping lanes are close enough to land to use shore based aircraft. Its far easier to enslave the local population to build an airstrip than to build an escort carrier
Here is interesting discussion of Japans convoys or lack there of.

Japanese Convoy Routes 1943-1945

Japanese Convoy Routes 1943-1945

www.academia.edu

The irony is that Japan had the perfect patrol bomber for their needs, the Lockheed Hudson, which they were producing under license. Japan has airbases in Kyushu, Okinawa, Formosa, and the Philippines that can provide complete coverage from Japan to Sumatra.
The problem of course is that the Tachikawa Type LO Transport Aircraft was a Army program and giving them to the navy would be unthinkable.

 

[SaparotRob]

The irony is that Japan had the perfect patrol bomber for their needs, the Lockheed Hudson, which they were producing under license. Japan has airbases in Kyushu, Okinawa, Formosa, and the Philippines that can provide complete coverage from Japan to Sumatra.
The problem of course is that the Tachikawa Type LO Transport Aircraft was a Army program and giving them to the navy would be unthinkable.

 

[Shortround6]

They don't need escort carriers. They are not crossing the Atlantic. Most of their important shipping lanes are close enough to land to use shore based aircraft. Its far easier to enslave the local population to build an airstrip than to build an escort carrier

It is about 2050 miles from the southern tip of Japan to northern Borneo. Yes there are a bunch of places you can build airfields for ground based aircraft. But not only do you have to build the airfields, you have to supply the aircraft, the man power, the fuel and food. Maybe you can get away with 6-7 airfields (and the one/s in Taiwan may already exist)
But a converted freighter with 12-18 planes traveling with a convoy may not be any more expensive.
But the Japanese never used large convoys. This is a difference in strategy/priorities that was rather wasteful.
Spreading the the merchant ships out is small groups meant that the the losses from a big raid would be small, but it also meant that the Americans had a much better chance of finding at least one convoy. It also meant that any one convoy didn't have the number of escorts needed to really defend even a small convoy. A 30 ship convoy does not need 3 times the escorts of a 10 ship convoy and certainly not 6 times the escorts of a 5 ship convoy.
Japanese Convoy escorts did not get high priority in sensors, commanders, or even AS weapons. This was somewhat masked in 1942 by the crappy US torpedoes and the sometimes less than stellar US commanders of that time.

 

[GrauGeist]

Some alternative IJA fighters:
- Ki 60, but powered by a good radial (say, Kinsei) from 1942 on - Ki 60 was with a smaller wing than the Ki-61, but the -61 was with a more refined cooling system that was less draggy, so even though the wing was bigger, the total drag remained the same
- Ki-44 with the better exhausts and water-alc injection
- Ki-44 with the Homare as a fighter tailored for the very high speed
- Ki-44 with the water-alc Ha 115-II (Sakae family), manufactured instead of the later Ki-43s
- definitely axe the Ki-45 as a fighter; even the Ki-60 with the 2-speed Ha 102 engine will bring more to the table, and can be produced almost two for each Ki-45 not produced (talk another 1500 fighters)
- take note of the Ha 42 engine, making a fighter around that engine might've been a good move
- don't fiddle with the Ki-43 - manufacture it as-is early on, and introduce the changes, like the butterfly flaps later, but don't forget the protection for the pilot and fuel (thus the Ki-27 can be phased out earlier)

Obviously, if the more advanced supercharges can be had for the respective engines, even better. As you can see, I avoid as a plague the two-engined fighters for Japan.

The IJA did attempt a turbo-supercharged fighter with the KI-87, but this project was woefully late.

 

[tomo pauk]

The IJA did attempt a turbo-supercharged fighter with the KI-87, but this project was woefully late.

Turbochargers for anyone but Americans were a tricky thing to pull off. One needs modern manufacturing capability to make them even in thousands, same for the materials suitable for high temperatures (nickel is the best, but availability of nickel for Axis in general was bad), as well as engineering capacity & time to design & test the apparatus (we can recall that it took years for the Americans to iron-out the bugs). Retrofit of the turbo system on a fighter is possible, but it is tricky. Volume required to fit the whole turbo system is substantial.
Two-stage mechanically driven superchargers don't require the fancy materials (same as the 1-stage superchargers everyone was making), knowledge pool is not as restricted as for the turboes, and retrofit on the existing fighters is far easier. There is no added bulk as much as on the turboed aircraft = good for streamlining = good for speed.

 

[EwenS]

It is about 2050 miles from the southern tip of Japan to northern Borneo. Yes there are a bunch of places you can build airfields for ground based aircraft. But not only do you have to build the airfields, you have to supply the aircraft, the man power, the fuel and food. Maybe you can get away with 6-7 airfields (and the one/s in Taiwan may already exist)
But a converted freighter with 12-18 planes traveling with a convoy may not be any more expensive.
But the Japanese never used large convoys. This is a difference in strategy/priorities that was rather wasteful.
Spreading the the merchant ships out is small groups meant that the the losses from a big raid would be small, but it also meant that the Americans had a much better chance of finding at least one convoy. It also meant that any one convoy didn't have the number of escorts needed to really defend even a small convoy. A 30 ship convoy does not need 3 times the escorts of a 10 ship convoy and certainly not 6 times the escorts of a 5 ship convoy.

Convoy routes

Maps of the Japanese convoy routes in 1942 with an indication of the traffic levels.

1. Multiple Facilities on Tsugaru Strait and Mutsu Bay
2. Tokyo, Japan
3. Matsusaka, Japan
4. Numerous Facilities on Honshu and Kyushu Islands, Japan
5. Shanghai, China
6. Tsingtao, China
7. Dalian, China
8. Incheon Korea
9. Ulsan, Korea
10. Gusan, Korea
11. Rason, Korea
12. Vladivostok, USSR
13. Nakhodka, USSR
14. Maizuru, Japan
15. Otaru, Japan

1. Taipei, Formosa
2. Kaohsiung, Formosa
3. Hong Kong, British Empire
4. Haikou, China
5. Sanya, China
6. Saigon, (Vichy) French Indochina
7. Bangkok, Thailand
8. Rangoon, British Burma
9. Singapore, British Empire
10. Tanjung Pandan, Dutch East Indies
11. Surabaya, Dutch East Indies
12. Miri, Malaysia, British Empire
13. Nunukan, Dutch East Indies
14. Senipah, Dutch East Indies
15. Manila, Philippines
16. Masbate City, Philippines
17. Dumaguete, Philippines
18. Palau Islands
19. Truk Lagoon
20. Rabaul, Territory of New Guinea
21. Wewak , Territory of New Guinea
22. To Wake Island
23. To Marshall Island

And how the convoy routes closed down in 1943-44 as the US advanced from the Solomons and the South Pacific.

Few things to note:-
1. Rabaul on New Britain became isolated from the end of 1943 by virtue of Operation Cartwheel and carrier strikes in Nov 1943.
2. Kwajalein in the Marshall Islands was invaded at the end of Jan 1944 in Operation Flintlock have been under attack for several months.
3. Operation Hailstone in Feb 1944 rendered Truk useless as a forward base
4. A major carrier strike hit the Palaus at the end of March 1944 before they were invaded in Sept. After Saipan fell the Palaus lost much of their importance as there were much safer routes to get ships back to Japan.
5. Hollandia was invaded in April after a month of air attacks by land and carrier based aircraft.
6. Operation Forager to take the Marianas got underway in June 1944. Firstly with Saipan in June and then Tinian and Guam through until mid-Aug.

Airfields

There were a lot more airfields around than you seem to realise. At least some of these dated from the pre-Pacific War era. Working south from Kyushu:-

Okinawa - an IJN airfield at Naha (Oruku) had existed since 1933. Others were added by the Japanese at some point. Machinato (Moshinawa), Yontan (Yomintan), Kadena, Ie Shima.

Sakishima Island group - airfields were built on Miyako (built by IJN in 1943), Iriomote & Ishigaki (built by the IJA in 1943)

Formosa / Taiwan - was well served by airfields by the start of the Pacific War. Matsuyama had been built in 1936 in the north near Taipei. Shinchiku in the north west was in use throughout the war. Kobi (Huwei) on the central west coast was another. There were at least 9 airfields in the south / south east area of the Island from which IJA & IJN aircraft flew from 8 Dec 1941. The rugged east coast didn't make for good airfield building territory.

Luzon -
Aparri airfield on the extreme north of Luzon existed from pre-war as an emergency field with 2 runways, and was captured by the IJA in Dec 1941.
Laoag on the northwest corner existed from pre-war and was captured by the IJA in Dec 1941.
Cabanatuan - a pre-war Philippine AF base in central Luzon north of Manila.
Olongapo / Subic Bay - a pre-war USN seaplane base.
There was a cluster of USAAF airfields around Manila in Dec 1941 - Iba, Nichols, Clark, Del Monte.
Batangas - a Philippine AF base from pre-war in central Luzon south of Manila.

Palawan (the long island between the Philippines & Borneo - there was a grass airfield at Puerto Princesa dating back before the war. A seaplane base and new airfield were built at Peurto Princesa by Allied POW from Sept 1942 to Sept 1944. The 150 survivors from the construction phase were massacred in Dec 1944, only 11 escaping.

Borneo
There were quite a number of Dutch airfields in Borneo that fell into Japanese hands as they advanced south:-
Sinkawang - west Borneo
Samarinda - east Borneo (north of Balikpapan and its large refineries)
Tarakan - north east Borneo

And British:-
Labaun (Labaun Island) - Sabah province at the north west end of the island.
Bintulu - north west Borneo - built 1937 & used as an emergency field in WW2.
Kuching - in the south west Pre-war civil airport captured in early 1942.
Sandakan - north Borneo. Under construction in Dec 1941. Completed by the Japanese using POW labour. OPerational in Dec 1942.

And more built by the Japanese:-
Miri (Lutong) in the north west - built by Japanese in WW2
Kudat on north tip of Borneo
Jesselton (Kota Kinbalu) - north east of Labaun
Keningau Airfield - northern Borneo built by Japanese in WW2
Ranau airfield - built by IJA in WW2

Look around the other islands in the DEI and you will find plenty of other airfields, some dating from pre-war & others of Japanese construction. Building airfields and keeping them supplied does not seem to have been a problem.

French Indochina - the Japanese built a clutch of airfields around Saigon between Sept & Dec 1941.

By 1944 much Japanese transport was by much smaller vessels, given various code names by the Allies or at least US forces. The term "junk" comes up in many RN reports..

It was these types of vessel that turn up most frequently in the details of air attacks on Japanese shipping in the late war period, often travelling alone and unescorted. It also accounts for the switch, at least amongst British subs, to use of the gun and boarding to place explosive changes as many of these smaller vessels were not worth a torpedo.

Looking at the details of the various "Standard" ships built in and by Japan the most notable thing is the size of the most numerous versions. Like 386 prefabricated Type 2E (870grt, 1,580dwt) general cargo ships built as part of their 1944 Programme. That compares to just 121 of the larger (6,600grt, 11,200dwt) Type 2A in the same programme. They also built 2,278 wooden ships between 1942 & 1945 usually sized at 100/150/250 tons. It was these smaller vessels that plied their trade around the coasts of Japanese occupied territory.

Japanese Convoy escorts did not get high priority in sensors, commanders, or even AS weapons. This was somewhat masked in 1942 by the crappy US torpedoes and the sometimes less than stellar US commanders of that time.

As for the priority of sensors and AS weapons, your statement is open to challenge.

The Etorofu and subsequent classes of Kaibokan entering service from mid-1943 had a Mod 93 sonar and Mod 93 hydrophone as a standard fit. It was replaced by 2 Type 2 sonars after April 1944 + the Mod 93 hydrophone. (see Warship 31 article by Hans Lengerer & Tomoko Rehm-Takahara). Type 22 surface search radar was also intended to be standard for the MIkura, Class B and later, and was certainly being fitted from late 1943 along with the Type 13 for air warning from 1944. Given that the first Japanese radar set of any kind only went to sea in April 1942 for the very first time, it was not a bad result.

As for the weapon load the above classes started with 36 Type 95 DC with one Type 94 thrower (equivalent to the USN Y thrower, discharging 2 charges at a time plus a loading frame. By the end of 1943 the DC load rose to 60 and then by 1945 to 120, with more throwers and racks.

 

[SaparotRob]

Convoy routes

Maps of the Japanese convoy routes in 1942 with an indication of the traffic levels.

View attachment 817022

1. Multiple Facilities on Tsugaru Strait and Mutsu Bay
2. Tokyo, Japan
3. Matsusaka, Japan
4. Numerous Facilities on Honshu and Kyushu Islands, Japan
5. Shanghai, China
6. Tsingtao, China
7. Dalian, China
8. Incheon Korea
9. Ulsan, Korea
10. Gusan, Korea
11. Rason, Korea
12. Vladivostok, USSR
13. Nakhodka, USSR
14. Maizuru, Japan
15. Otaru, Japan


View attachment 817023

1. Taipei, Formosa
2. Kaohsiung, Formosa
3. Hong Kong, British Empire
4. Haikou, China
5. Sanya, China
6. Saigon, (Vichy) French Indochina
7. Bangkok, Thailand
8. Rangoon, British Burma
9. Singapore, British Empire
10. Tanjung Pandan, Dutch East Indies
11. Surabaya, Dutch East Indies
12. Miri, Malaysia, British Empire
13. Nunukan, Dutch East Indies
14. Senipah, Dutch East Indies
15. Manila, Philippines
16. Masbate City, Philippines
17. Dumaguete, Philippines
18. Palau Islands
19. Truk Lagoon
20. Rabaul, Territory of New Guinea
21. Wewak , Territory of New Guinea
22. To Wake Island
23. To Marshall Island

And how the convoy routes closed down in 1943-44 as the US advanced from the Solomons and the South Pacific.
View attachment 817024

Few things to note:-
1. Rabaul on New Britain became isolated from the end of 1943 by virtue of Operation Cartwheel and carrier strikes in Nov 1943.
2. Kwajalein in the Marshall Islands was invaded at the end of Jan 1944 in Operation Flintlock have been under attack for several months.
3. Operation Hailstone in Feb 1944 rendered Truk useless as a forward base
4. A major carrier strike hit the Palaus at the end of March 1944 before they were invaded in Sept. After Saipan fell the Palaus lost much of their importance as there were much safer routes to get ships back to Japan.
5. Hollandia was invaded in April after a month of air attacks by land and carrier based aircraft.
6. Operation Forager to take the Marianas got underway in June 1944. Firstly with Saipan in June and then Tinian and Guam through until mid-Aug.

Airfields

There were a lot more airfields around than you seem to realise. At least some of these dated from the pre-Pacific War era. Working south from Kyushu:-

Okinawa - an IJN airfield at Naha (Oruku) had existed since 1933. Others were added by the Japanese at some point. Machinato (Moshinawa), Yontan (Yomintan), Kadena, Ie Shima.

Sakishima Island group - airfields were built on Miyako (built by IJN in 1943), Iriomote & Ishigaki (built by the IJA in 1943)

Formosa / Taiwan - was well served by airfields by the start of the Pacific War. Matsuyama had been built in 1936 in the north near Taipei. Shinchiku in the north west was in use throughout the war. Kobi (Huwei) on the central west coast was another. There were at least 9 airfields in the south / south east area of the Island from which IJA & IJN aircraft flew from 8 Dec 1941. The rugged east coast didn't make for good airfield building territory.

Luzon -
Aparri airfield on the extreme north of Luzon existed from pre-war as an emergency field with 2 runways, and was captured by the IJA in Dec 1941.
Laoag on the northwest corner existed from pre-war and was captured by the IJA in Dec 1941.
Cabanatuan - a pre-war Philippine AF base in central Luzon north of Manila.
Olongapo / Subic Bay - a pre-war USN seaplane base.
There was a cluster of USAAF airfields around Manila in Dec 1941 - Iba, Nichols, Clark, Del Monte.
Batangas - a Philippine AF base from pre-war in central Luzon south of Manila.

Palawan (the long island between the Philippines & Borneo - there was a grass airfield at Puerto Princesa dating back before the war. A seaplane base and new airfield were built at Peurto Princesa by Allied POW from Sept 1942 to Sept 1944. The 150 survivors from the construction phase were massacred in Dec 1944, only 11 escaping.

Borneo
There were quite a number of Dutch airfields in Borneo that fell into Japanese hands as they advanced south:-
Sinkawang - west Borneo
Samarinda - east Borneo (north of Balikpapan and its large refineries)
Tarakan - north east Borneo

And British:-
Labaun (Labaun Island) - Sabah province at the north west end of the island.
Bintulu - north west Borneo - built 1937 & used as an emergency field in WW2.
Kuching - in the south west Pre-war civil airport captured in early 1942.
Sandakan - north Borneo. Under construction in Dec 1941. Completed by the Japanese using POW labour. OPerational in Dec 1942.

And more built by the Japanese:-
Miri (Lutong) in the north west - built by Japanese in WW2
Kudat on north tip of Borneo
Jesselton (Kota Kinbalu) - north east of Labaun
Keningau Airfield - northern Borneo built by Japanese in WW2
Ranau airfield - built by IJA in WW2

Look around the other islands in the DEI and you will find plenty of other airfields, some dating from pre-war & others of Japanese construction. Building airfields and keeping them supplied does not seem to have been a problem.

French Indochina - the Japanese built a clutch of airfields around Saigon between Sept & Dec 1941.

By 1944 much Japanese transport was by much smaller vessels, given various code names by the Allies or at least US forces. The term "junk" comes up in many RN reports..
View attachment 817033

It was these types of vessel that turn up most frequently in the details of air attacks on Japanese shipping in the late war period, often travelling alone and unescorted. It also accounts for the switch, at least amongst British subs, to use of the gun and boarding to place explosive changes as many of these smaller vessels were not worth a torpedo.

Looking at the details of the various "Standard" ships built in and by Japan the most notable thing is the size of the most numerous versions. Like 386 prefabricated Type 2E (870grt, 1,580dwt) general cargo ships built as part of their 1944 Programme. That compares to just 121 of the larger (6,600grt, 11,200dwt) Type 2A in the same programme. They also built 2,278 wooden ships between 1942 & 1945 usually sized at 100/150/250 tons. It was these smaller vessels that plied their trade around the coasts of Japanese occupied territory.





As for the priority of sensors and AS weapons, your statement is open to challenge.

The Etorofu and subsequent classes of Kaibokan entering service from mid-1943 had a Mod 93 sonar and Mod 93 hydrophone as a standard fit. It was replaced by 2 Type 2 sonars after April 1944 + the Mod 93 hydrophone. (see Warship 31 article by Hans Lengerer & Tomoko Rehm-Takahara). Type 22 surface search radar was also intended to be standard for the MIkura, Class B and later, and was certainly being fitted from late 1943 along with the Type 13 for air warning from 1944. Given that the first Japanese radar set of any kind only went to sea in April 1942 for the very first time, it was not a bad result.

As for the weapon load the above classes started with 36 Type 95 DC with one Type 94 thrower (equivalent to the USN Y thrower, discharging 2 charges at a time plus a loading frame. By the end of 1943 the DC load rose to 60 and then by 1945 to 120, with more throwers and racks.

 

[z42]

Volume required to fit the whole turbo system is substantial.

What enabled modern turbos to be so much more compact? Was it mostly better alloys allowing a smaller hotter faster spinning turbine, or where there other major factors?

 

[tomo pauk]

What enabled modern turbos to be so much more compact? Was it mostly better alloys allowing a smaller hotter faster spinning turbine, or where there other major factors?

Probably the better materials, as well as more understood & developed water cooling system (air was preferred method of cooling back in ww2). Decades of development of turbines for the jet engines certainly played the part here. Small size of the turboes for cars probably also played the part.
On the 'normal' cars of today, the turbo system will still populate the volume under the hood by a good deal. In many cases, a 200 HP 4 cyl 2 liter engine with the turbo will demand probably as much of the volume as it will be the case with the 200 HP 6 cyl 3 liter naturally aspirated engine. Granted, a 4 cyl 2 liter engine can be pushed to 300, 400 or even 500 HP easily & cheaply today, while the 3 liter V6 n-a engine will be lucky to get to 300 HP, even after the very expensive engine rebuild.
On the combat aircraft, the inside volume is already accounted for, and it is a 'home' for different systems and items - meaning that the free volume 'under the hood' is as good as non-existing (unless it is well away from the centre of gravity, a thing that cars are not as susceptible as aircraft).

Sometimes the 'remote' turbo is added to the 'normal' cars, if there is a wish for a big turbo and a car has no spare volume in front of the cabin. Video from our favorite Bosnian youtuber.