Japanese logistics, purchase programs and war booty, reality and alternatives 1936-44 (1 Viewer)

[Shortround6]

If Wiki is right and the main change of the Mod 5 is the stronger buffer springs, I'd imagine it would be relatively easy to introduce that earlier in the timeline, no? The fire rate doesn't need to be stratospheric, but 480~500 rpm is unnaceptable for a 20 mm.

The 20mm Oerlikon traces back to the Becker gun of 1915 (patent was from 1913).
Order for 120 guns was placed in June 1916. By the end of the war The Allies found 362 guns, actual production is unknown. 1921 saw the transfer of the rights to the SEMAG of Switzerland.
Ehrhardt was working on a competing gun in WW I that was short recoil, scaled up from the Dreyse machine gun of 1912. Perhaps 51 guns were built(?) all but a few disappeared at the end of the war. Rights were transferred to Solothurn.
Granted in 1920s the world was not rushing to by new weapons but they had just under 20 years to work on them before WW II broke out. You also have a number of arms designers (mostly in Europe) trying to design alternatives that were lighter, more powerful, faster firing and any other improvement you can think of. The The Oerlikon F started at about 300rpm, slightly up from the 250-300rpm of the WW I guns. They got around 400rpm out of it by the early 30s. Different accounts use different numbers (different tests or advertisements?) By WW II the shorter guns were getting into the low 500rpm range.
The long cartridge FFS never really got over 500rpm during WW II and many of 1930s versions were barely over 400rpm.
There were a lot of people making Oerlikon guns of different sizes in different countries for a number of years from the mid 30s to end of WW II. And all somebody had to do was change the spring?
Wiki is correct, basically, that is the major change. But getting the gun to function correctly using all ammo types and in all conditions is a lot harder. See the trouble the Germans had with the MG FF and MG FFM. You can load the older FF ammo into the magazines of the FFM and the gun will fire, at least for a short time.
I will note that nobody says you can take an FF and turn it into an FFM simply by changing the spring.
I will also note that the 20mm FFS series of guns (ground AA) required lubricated ammo (greased/waxed) to function reliably in different weather conditions. And a cold gun is going operated differently than a hot gun.
The API blowback system of the Oerlikon guns requires a careful balance of reciprocating weight, initial spring pressure and spring pressure/tension throughout the bolt travel balanced against the pressure in the chamber/barrel. It is getting the balance correct that requires a lot of time/testing.

 

[Shortround6]

See it from the Japanese PoV. A pair of Ho-3 cannons (plus perhaps a pair of LMGs for the feel-good feeling) is far cry vs. even the heaviest firepower the Ki-43 had. Even the Ki-43 and Ki-61 were initially with just 2 LMGs and 2 HMGs.
I have nothing against the better and more refined weapon, just that this is available historically, and can do the job until these better weapons arrive.

The Japanese needed a heavier, more powerful fighter than the Ki-43. A big wing Ki-44 (think primitive Ki-84) might have been able to carry a pair of Ho-3 cannon. Now the question is is if a single slow firing Ho-3 in each wing was better than a pair of 12.7 Ho-103s in each wing or a pair of Navy type 99-Is ?

Japanese-produced guns were generally pretty light, from 30 to 50 kg.

That is true but the lighter guns tend to use smaller, lower powered ammo. Gun designers were not stupid. They often worked to different requirements. Gun designers did not tell the Generals and Admirals what they needed. They might suggest what they thought they could do but the 'brass hats' wrote the requirements and issued the contracts.
Some real big unknowns were both the required reliability (jams/malfunctions per 1000 rounds?) and durability (life of the gun). Soviets traded durability for weight.
Japanese emphasized light weight armament to get high performance aircraft.
US saddled a lot of their early war aircraft with way too much weight in guns and ammo.

 

[tomo pauk]

The Japanese needed a heavier, more powerful fighter than the Ki-43. A big wing Ki-44 (think primitive Ki-84) might have been able to carry a pair of Ho-3 cannon. Now the question is is if a single slow firing Ho-3 in each wing was better than a pair of 12.7 Ho-103s in each wing or a pair of Navy type 99-Is ?

There is no such thing as an ideal historical ww2 gun?
A Ki-44 might've worked as-is with a pair of either Ho-3s or the Navy's cannons. Sprinkle with some HMGs or LMGs to taste.
The FFL might've been the best fit - it was not some awesome 20mm weapon, but it has no actual shortcomings (be that in weight, size, RoF or MV), bar the late start as far as the Japanese go. It's slender ammo was also a bonus, more could be packed in the volume than the bottlenecked 20mm rounds.

That is true but the lighter guns tend to use smaller, lower powered ammo. Gun designers were not stupid. They often worked to different requirements. Gun designers did not tell the Generals and Admirals what they needed. They might suggest what they thought they could do but the 'brass hats' wrote the requirements and issued the contracts.
Some real big unknowns were both the required reliability (jams/malfunctions per 1000 rounds?) and durability (life of the gun). Soviets traded durability for weight.
Japanese emphasized light weight armament to get high performance aircraft.
US saddled a lot of their early war aircraft with way too much weight in guns and ammo.

Japanese 20mm stuff was pretty reliable, or, at least there are no Allied reports on these being problematic. Perhaps the people designing and making guns were simply good in what they were doing?
The HMGs were decent by mid-war, but going with HE stuff on the HMGs was both not worth it (bang for buck) and IIRC was cause of premature detonations on the Ki-43.

 

[Shortround6]

There is no such thing as an ideal historical ww2 gun?
A Ki-44 might've worked as-is with a pair of either Ho-3s or the Navy's cannons. Sprinkle with some HMGs or LMGs to taste.
The FFL might've been the best fit - it was not some awesome 20mm weapon, but it has no actual shortcomings (be that in weight, size, RoF or MV), bar the late start as far as the Japanese go. It's slender ammo was also a bonus, more could be packed in the volume than the bottlenecked 20mm rounds.

You are correct, there was no 'ideal' 20mm historic WW 2 gun.
The Hispano was good, but it took a while and it was heavy, there was no powerful but light gun. Sort of pick one or the other
The FFL/type 99-2 might have been good, not the best but it was closer to the Hispano while weighing less.
The Ho-3 ammo was fat, About 7mm or about 33% fatter than the 20 x 72RB and 20 x 99RB of the Japanese Oerlikons. Not so important with the 50-60 round magazines/drums but when you are heading towards 100 rounds and the fatter shells will only allow around 75 instead if 100?

Japanese 20mm stuff was pretty reliable, or, at least there are no Allied reports on these being problematic. Perhaps the people designing and making guns were simply good in what they were doing?
The HMGs were decent by mid-war, but going with HE stuff on the HMGs was both not worth it (bang for buck) and IIRC was cause of premature detonations on the Ki-43.

Most WW II guns were not built on the cheap model, except some Soviet guns and a few German? That came later.
Just pointing out the trying for a light weight gun can have consequences. That is lighter than average for the performance. You can have a light gun that is reliable and long lasting if you give up some performance factors. Japanese had been fighting in China for a number of years, slowly expanding southward. They had also been operating in Manchuria for a while and were familiar with supply/logistics.
Japan was also a small country Industry wise. There was not the car industry or even an industry that made large numbers of washing machines or refrigerators. Car production was more on the order of 0.1% rather than even 1% of US production. Or even less. Under 12,000 trucks buses and cars built in 1939? A lot of their steel production went to the Military even in the 1930s. There wasn't a lot of industry to convert over.
The Japanese did a lot of good work but they also didn't have the engineers and technical people. The US had enough people and enough resources to train people during the war, It was not unlimited but the US Industry also planed for schools or training areas to train people for weeks or months before they stuck them into a number of jobs in the factories. Not training on the job as an apprentice. The American way got more people semi-trained faster. It might not have given more well trained (higher skill levels) after one or more years.

The whole 12.7mm explosive bullet idea might have been a mistake, for any nation. The Japanese were trying to do away with the expensive fuse.
A 12.7mm round held around 1/5 to 1/10 of the HE of a 20mm shell. If you used a fuse it did not cost only 1/5 to 1/10 as much because it was smaller.
But 12.7mm AP or incendiary (no fuse) may show a large advantage over 7.7mm bullets.

 

[tomo pauk]

The Ho-3 ammo was fat, About 7mm or about 33% fatter than the 20 x 72RB and 20 x 99RB of the Japanese Oerlikons. Not so important with the 50-60 round magazines/drums but when you are heading towards 100 rounds and the fatter shells will only allow around 75 instead if 100?

This is the reason why I was suggesting that the 20mm ammo should've been necked-up to 23mm, as well at the "Ho-3/23" is made - since we're already paying the price in bulk and weight, have it at least provide a considerably greater punch than the 20mm stuff. A 180-200 g shell vs. ~130g?

The whole 12.7mm explosive bullet idea might have been a mistake, for any nation. The Japanese were trying to do away with the expensive fuse.
A 12.7mm round held around 1/5 to 1/10 of the HE of a 20mm shell. If you used a fuse it did not cost only 1/5 to 1/10 as much because it was smaller.
But 12.7mm AP or incendiary (no fuse) may show a large advantage over 7.7mm bullets.

Yes, the AP(I) is the way for any HMG, IMO.

 

[z42]

This is the reason why I was suggesting that the 20mm ammo should've been necked-up to 23mm, as well at the "Ho-3/23" is made - since we're already paying the price in bulk and weight, have it at least provide a considerably greater punch than the 20mm stuff. A 180-200 g shell vs. ~130g?

For aircraft autocannons there might be a case to be made for a relatively short and stubby shell giving decent enough MV with a more or less straight walled cartridge? Not as efficient ballistically as a thinner and longer shell of the same weight, but at realistic shooting ranges might not matter.

Yes, the AP(I) is the way for any HMG, IMO.

Agreed.

 

[marathag]

Kayaba Ka-1 Autogyro

based off US design, was a good utility aircraft used by the IJA.

Including ASW, from the Army Escort Carriers, since the IJN was so bad at ASW.

Make more, and for both service Branches. Then work on improved models with more payload.

 

[tomo pauk]

For aircraft autocannons there might be a case to be made for a relatively short and stubby shell giving decent enough MV with a more or less straight walled cartridge? Not as efficient ballistically as a thinner and longer shell of the same weight, but at realistic shooting ranges might not matter.

From what I can gather, most of the times people went with a (very) powerful cartridge, the resulting gun for that cartridge was with major shortcomings as a gun for air fighting. Either the gun was too big to fit neatly, or it was very heavy, or it recoiled badly, or the RoF was slow, or the ammo count was low, or the shell was too light, or a combination of the above. Now, such guns would've be doing great as AA pieces, or even as flying AT artillery, but installing them on a modestly-sized fighter was a tough job.

So yes indeed - aim for a more modest MV (but not too modest), that keeps the gun recoil, size & weight manageable, RoF is good, shell weight & count is good; basically, one has a good/great gun to fight aerial targets on the normally short distances in the ww2.

 

[GrauGeist]

I believe Snowygrouch referenced this as well in one of his posts but I could not find it using Snowygrouch, as the search term is no longer usable due to his leaving the

Callum's user name is hard to search for, but I was able to find it via his Secret Horsepower Race book thread:

"The Secret Horsepower Race" - Available to pre-order

 

[z42]

Related to Japanese logistics, here's an excellent discussion between two historians that touches on Japanese logistics deficiencies.


View: https://www.youtube.com/watch?v=njd2xvMcTx8

So they conquer DEI with its oil, Malaya which was the rubber capital of the world at the time, and then they lack the logistics capacity to actually make use of these conquered resources! Yes, even before US subs sank a lot of their merchant ships.

 

[Shortround6]

Resurrecting an old thread.

A number of the ammo types the two branches used, just between 7.7 and 37mm, was staggering. Three LMG ammo types (the 7.7mm were not interchangable), two HMG calibres, five (!) 'local' 20mm ammo types + the MG 151/20, three 30mm, three(?) 37mm. I've probably missed some.

You have actually under stated the problem. Japanese used three different 7.7mm rifle/MG rounds in addition to the 6.5mm ammunition and some of the 6.5mm machine guns could not use the full power rifle ammo (or only in emergency).
In addition to the Japanese LMG calibers both the Army and Navy adopted the German MG 15 aircraft gun in 7.9 x 57. I have no idea if they used captured Chinese ammo or not.
The 7.9 x 57 was the 'standard' Chinese rifle/mg round, as much as anything was standard in China at the time.

There were three types of HMG ammo. Japanese Army and Navy both adopted small numbers of the German MG 131 guns and the 13mm ammo to suit (percussion primed) in addition to the 13.2mm Hotchkiss ammo and the British/Italian 12.7mm ammo. They didn't use all than many MG 131s but the question is why?

There may have been six different Japanese 20mm rounds before the MG 151/20 showed up. The 20 x 99RB used in the Army type 94 gun did not see much use. Only as a flexable in some heavy bombers.
Three 30mm seems to be correct. Not sure about three 37mm. There seem to have been three 37mm aircraft guns. One of which was simply a single shot ground gun stuck in an aircraft and hand loaded. Number of army guns (infantry/tank/antitank could push the number higher with ease.

2-3 40mm guns. 3 if we count captured Bofors guns.
I don't think even the Soviets had to deal with such a number of different guns/calibers even getting lend/lease from the Americans and British.

One HMG type will suffice, so will a decent 30mm. Adopting any German automatic weapon is probably not worth it.

It might not be quite that simple. And a lot depends on timing.
The Japanese navy adopted the 13.2mm Hotchkiss in the early 30s (?) Army got some for AA use in mid 30s.
So they had ammo, but the Hotchkiss was heavy and slow firing and fed with a 30 round box. A terrible aircraft gun.
Army wanted a much lighter/faster firing aircraft gun. Navy went for the 20mm and only later used the Hotchkiss ammo in an adopted Browning action to counter the US .50.
Why both services adopted the German MG 131 instead of just using the army 12.7mm Ho-103 I have no idea. MG 131 was lighter and bit faster firing but perhaps the best was the enemy of good?
Japanese could not agree on what a good 30mm gun was. Weight or rate of fire or weight of shell (Japanese varied from 235 grams to 350 grams) or velocity. First Japanese 30mm used a 42 round drum.
Japanese adopted (built under license) the MG 15 and the MG 131. Perhaps not needed but the Japanese 7.7mm defensive machine guns were a pretty sorry lot of guns. MG 15 had a higher rate of fire and was belt fed. A British Vickers K gun would have been an improvement over most of them.
I have no idea why the Japanese could not have come up with flexible 1000-1200rpm light gun of their own. Or why they almost never mounted them in pairs.

Army should not forget to specify cannons for their 1-engined fighters as early as possible.

Or at least multiple 12.7/13mm machine guns (more than 2).
The "famous" 40mm Ho-301 should never have seen the light of day outside of a research lab.

Japanese needed stuff that would work in 1942-43. Anything that showed up in 1944 was too late.

 

[Shortround6]

My own opinion is that the Japanese needed to do more before Pearl Harbor and immediately after.
By mid 1943 anything they did was going to be too late. Shooting down 50-100 more B-29s in 1945 was only going to delay things by a few days at best.
Japanese over-reacted to the Doolittle raid in 1942. They pulled back too many fighters and AA guns.
Their best defense was keeping the Americans at a further distance from the home Islands.
They needed to defend their front-line bases more than they needed to defend the home Islands.

It still would not have worked but building 100-127mm heavy AA guns for home defense means that the war is already lost and lost bad enough that the Japanese are not going to get much from any peace treaty.
Slowing the American advance in 1942-43 had a slim chance (very slim) of getting the peace (surrender) talks going.
that said

Air defenses:
- buy the licence for the 40mm Bofors (for both Army and Navy needs), don't bother with the 25mm AA gun from France

Pretty much a given for just about all nations.

- the Japanese 20mm AA guns are just fine, Navy should have these in production for their needs

Japanese Army 20mm may have been better than the Navy (French) 25mm but that is damning with very faint praise.

The gun/ammo was powerful. It was also slow firing, heavy and awkward. It fired just a bit faster than the German 20mm Flak 30 but adopting it in 1938 when the Germans were moving to the faster firing Flak 38 ? A single shot from this gun was about 1/3 more powerful than the ammo used in Flak 30/38.

1st round on left (red shell) is 20mm Hispano. 4the round (20x125) is the Japanese AT and Japanese Army early Aircraft round. 5th round (20x138) is the German 20mm army round.
The 7th round (20x142) is the Japanese army AA gun round. Using more than 20 round magazines is possible but difficult. Japanese managed to get the Type 98 up to around 450rpm but only late in the war (?) Using it as a free-swinging gun like an Oerlikon was probabley not a good idea.
It may have been better than the single 25mm guns the Japanese did use but that didn't work well at all.

- seems like the 100 and 120-127mm guns were the best what Japan had wrt. the heavy AA guns, but these are unlikely to be manufactured en masse as needed, so something else is also needed, preferably the German 8.8cm, or even the Bofors 75mm AA gun that Japanese actually copied, if too late

Kind of covered above. Japanese needed something along the line of the 75mm Bofors gun to start with and they needed them on the forward bases.
These guns are significantly smaller/lighter than the German 88mm and the Japanese should be able to build more for the same cost. And buy more shells.
Make it harder for the Americans to bomb the Japanese airfields and harbors.

- increased and early cooperation with Germany should've introduced the Japanese with the advantages of the gun-laying radar

Japanese need a better electronics industry. The problem is not so much ideas but production. Very few Japanese ships had any sort of radar in early 1943 let alone gun laying radar.
Japanese needed search or early warning radar before worrying about gun laying radar and they needed on scores of ships and dozens of Islands.
Japanese needed better radios in the aircraft, or better spark plug wires so the ignitions systems didn't interfere/jam their own radios.

The Japanese captured very little war booty in the form of hardware. A few dozen 75/80mm guns in the DEI weren't going to make much difference or a few dozen 40mm Bofors guns in Malaya. Show the Japanese what was possible or what they could be soon facing but they needed 2-3 years to get things into production and that is at best.

 

[EwenS]

Regarding Japan and the 40mm Bofors, they tried (unsuccessfully) to develop their own version from British guns captured at Singapore. From the Navweaps site.



Japan Weapons and Mountings

The Type 5 (Model 1945) originated from the capture at Singapore in 1942 of 24 British Bofors single air-cooled guns in working condition and another 56 made serviceable after repairs. One of these was used to produce a Japanese copy and this underwent prototype firing trials in 1943 at the Torigasaki range of the Yokosuka Naval Arsenal. Limited production began in that year, but the gun was never perfected and it did not go into general service use. However, some 5 to 7 weapons a month were being produced in late 1944, apparently for service evaluation purposes. The main alteration from the British Bofors design was to increase the bore length to 94.49 in (2.400 m) - 60 calibers - and to add Rhienmetall-style flash suppressors, which proved unsatisfactory. Production was at the Yokosuka Naval Arsenal and at the Hitachi Manufacturing Company. Used only in manually-worked single mountings, which had an elevation range of -10 / +95 degrees and a weight of 1,870 lbs. (850 kg). Recoil was 8.5" (21.6 cm). Major problems found by the USN after the surrender were that poor manufacturing practices and lack of quality control caused improper seating of rounds and jamming of parts and that the star wheels and extractors were frequently mismated.
Nomenclature Note: Although the Japanese designation is normally described as the Type 5 (Model 1945), "US Naval Technical Mission to Japan report O-47(N)-2" at one point (page 16) describes the Mechanism designation as "Type 5 (1943)," which cannot be correct as the numbers do not match. This error may imply that the designation would actually be "Type 3" (Model 1943) which would seem to be more in keeping with the actual Japanese design date of 1943. However, it should be noted that the Japanese Model number system, normally based upon the year the breech design was started, became very chaotic towards the end of World War II, with new weapons having Type years that had no relationship to the actual year that the breech design was started. So, this weapon may indeed have been designated as Type 5.

USA Bofors 40 mm L/60 Model 1936 - NavWeaps

navweaps.com

 

[Reluctant Poster]

Easy tiger, no one's ranting here except you. I read your post, clearly despite your statements you STILL don't get it. Just because the Japanese knew about the Hudson doesn't mean they needed it or were gonna do that for the reasons that you even said in your post yet you STILL argue the Japanese should'a because magazine articles? Your presumption is failing you despite yourself. By the way, the Hudson entered RAF service in May 1939, the first one did not fly until very late 1938.

Sorry pussy cat, I never said should . If you can't gasp that I cant help that.

 

[Shortround6]

A big question for me is why was the Hudson so good at ASW?

In British service it's 'competition' was the Anson, the Blenheim, the Whitley and Wellington.

What makes a good ASW aircraft?
1. Vision, the crew has to see the sub radar helps but I don't think anybody used radar bombing against subs 3-5 crewman seemed to give good visual spotting coverage.
2. Range, you have to get the plane to where the subs are in order to see them.
3. Enough speed to turn a sighting into an attack. How many seconds from spotting to dropping bombs/depth charges? German subs could dive in around 30 seconds give or take 10 seconds depending on model of U-boat and training.
4. bombload/attack pattern. Anson well and truly sucked. In part because the 100lb AS bomb well and truly sucked. two nearly useless bombs gave a small pattern and even direct hits often failed to damage the sub enough to prevent it from returning home. Hudson could carry up to ten such bombs and drop more per attack run (all?). Hudson could also carry 3 or 4 250lb depth charges or bombs. Whitleys and Wellingtons could carry more but rarely carried more than 2000lb worth, they want more fuel for more endurance/patrol time.
5. In British service the Hudsons had a very good reputation for making it home. Hudsons could fly on one engine. Especially later Marks that had feathering propellers. Many/most of the early British ASW aircraft had a negative climb rate with one engine out due to being under powered and having crappy propellers.

For the Japanese, are they using crappy propellers?
How reliable are their engines?
Can the plane stay in the air on one engine with bombs gone and some of the fuel gone?
Weight and drag of the aircraft vs the max continuous power of the engine.

 

[GrauGeist]

The Japanese didn't have a purpose-built ASW patrol bomber until the Kyushu Q1W entered service in January 1945.

It was not really all that impressive, performance-wise.

 

[Shortround6]

The Japanese didn't have a purpose-built ASW patrol bomber until the Kyushu Q1W entered service in January 1945.

It was not really all that impressive, performance-wise.

Very true in a number of ways.
Range of around 800 miles means a not great endurance at even 150mph.
Crew of three is sort of a minimum and vision out the side and rear is also important. Different angle's are important for spotting ships/wakes in less that good conditions.
Two bombs is not good. Four (even if smaller) is better for a wider/longer pattern.
Not sure if top speed (and range) is with or without the external bomb load.

Any ASW plane is better than no ASW plane but the Japanese had how many years to figure this out???
A least they didn't copy the Botha

 

[EwenS]

Very true in a number of ways.
Range of around 800 miles means a not great endurance at even 150mph.
Crew of three is sort of a minimum and vision out the side and rear is also important. Different angle's are important for spotting ships/wakes in less that good conditions.
Two bombs is not good. Four (even if smaller) is better for a wider/longer pattern.
Not sure if top speed (and range) is with or without the external bomb load.

Any ASW plane is better than no ASW plane but the Japanese had how many years to figure this out???
A least they didn't copy the Botha

A few points about Japanese airborne ASW.

Firstly convoy routes. Note their general close proximity to land. It was the routes between the DEI and Japan where the greatest losses were suffered.

Locations of losses of IJN warships which correlates to a large extent with the above convoy routes.

Then US estimate of Japanese merchant ship losses

Note the huge increase in losses in Q4 1943 when USN policy on targeting merchant shipping changed.

Link all that together and the Japanese had far less need for long ranged ASW aircraft compared to the Allies. They used a multitude of types for ASW, from Kawanishi H8K Emily flying boats, through G3M Nell and G4M Betty bomber types to smaller single engined types like B5N Kate & B6N Jill torpedo bombers etc etc. Identifying Japanese ASW aircraft units is far more difficult than for Allied units.

The US Naval Technical Mission studied Japaneee ASW in late 1945. A summary of their work can be found here.

HyperWar: War Damage Report 58: Submarine Report [Section 3]

 

[tomo pauk]

Japanese Army 20mm may have been better than the Navy (French) 25mm but that is damning with very faint praise.

If a 20mm AA gun is appreciated to be in the league of a then-current 25mm AA gun, the praise is honest.
But again, the main star of the light AA outfit needs to be a modern 40mm automatic, or at least a good, powerful 37mm automatic. 20mm is the second violin.

Kind of covered above. Japanese needed something along the line of the 75mm Bofors gun to start with and they needed them on the forward bases.
These guns are significantly smaller/lighter than the German 88mm and the Japanese should be able to build more for the same cost. And buy more shells.
Make it harder for the Americans to bomb the Japanese airfields and harbors.

Yeah, the Type 88 was behind the curve. The Navy's Type 98 was much more powerful.
Until 1945, Japanese were not that hard pressed with US bombers bombing from 25000 ft as it was the case with Germany, or with Japan itself in 1945, so a - good - 75mm might've been a very good asset. Again, some sort of a radar, or at least the Navy's modern optical fire control system would've been needed against the US bomber sorties.

Japanese need a better electronics industry. The problem is not so much ideas but production. Very few Japanese ships had any sort of radar in early 1943 let alone gun laying radar.
Japanese needed search or early warning radar before worrying about gun laying radar and they needed on scores of ships and dozens of Islands.
Japanese needed better radios in the aircraft, or better spark plug wires so the ignitions systems didn't interfere/jam their own radios.

The Japanese captured very little war booty in the form of hardware. A few dozen 75/80mm guns in the DEI weren't going to make much difference or a few dozen 40mm Bofors guns in Malaya. Show the Japanese what was possible or what they could be soon facing but they needed 2-3 years to get things into production and that is at best.

Very true.

For the Japanese, are they using crappy propellers?
How reliable are their engines?
Can the plane stay in the air on one engine with bombs gone and some of the fuel gone?
Weight and drag of the aircraft vs the max continuous power of the engine.

Japanese engines were very reliable, bar Homare and the too-smart-for-their-own-god Kasei versions. But an ASW aircraft will be powered by the 2nd tier engines anyway, talk Zuisei, Kinsei or Sakae. IIRC Japanese were making multi- engined aircraft that were good enough in the engine-out situation.

Their ability to mass-produce yet another 2-engined type is much a bigger problem than their ability to make a good aircraft and engine. Ruthless reduction on aircraft types, and the removal of desire to make many aircraft floatable would've helped them a lot.

 

[Shortround6]

A few points about Japanese airborne ASW.

Firstly convoy routes. Note their general close proximity to land. It was the routes between the DEI and Japan where the greatest losses were suffered.

Thank you for the information.
The Japanese needed endurance rather than range. A small distinction but important. A single aircraft orbiting a convoy can keep the sub/s down and no WW II diesel/electric boat can keep up with even a 7kt convoy for very long (2 hours?) except for the German Type XXI boats.
Longer endurance aircraft can stay on station a higher percentage of the time. A six hour aircraft can stay on station twice as long as 4 hour aircraft if both are flying one hour each way between base and patrol area/convoy. You need fewer aircraft total for the same coverage. Using mixed type of aircraft or at least mixed bomb loads might also help. Using two bombs per aircraft consistialy might lead to subs coming up once the first two bombs hit the water. Sub gambles that the 2nd aircraft is several hours away?
Japanese used small convoys with (mostly) one or two escorts. a 20 ship convoy does not need 5 times the escorts of a 4 ship convoy.
Use of numerous land bases means less need for convoy carriers.