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

[EwenS]

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.

Well one reason for smaller convoys is that the waters around the DEI and South China Sea were not the Atlantic. Many more navigational difficulties. Shallow waters, reefs etc. Take a look at detailed map of the SCS, where today the Chinese are building bases, and you will get the idea.

 

[Shortround6]

f a 20mm AA gun is appreciated to be in the league of a then-current 25mm AA gun, the praise is honest.

The Army 20mm and the navy 25mm had similar problems. A low rate of fire and small ammo capacity. The Army 20mm was faster firing than the 25mm but even the best Army 20mm was around 2/3rds the rate of fire of the Oerlikon gun. The 'extra' range of the 25mm was largely an illusion due to crappy sights, heavy vibration when firing and large muzzle flash. But the 25m was large, heavy and did not traverse or elevate quickly so it didn't work well against short range targets either. Japan should had taken out a license for the Oerlikon FFS when they got the licnces for the Ff and FFL, at least they all use the same projectiles.

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.

get license for the Italian Breda 37mm AA gun? Modify it but keep the water cooling?

Yeah, the Type 88 was behind the curve. The Navy's Type 98 was much more powerful.

The Type 98 was a little too ambitious. 600 round barrel life? Dial back the velocity some and double the barrel life? Just need to keep the allied bombers honest. Make them fly higher than they would like/increase miss distances.

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.

Unfortunately the Japanese need twins because of distances. Whatever big singles they can build in 1944 are too late. They need to do a better job in 1942 and early 1943. They need to really STOP the allies in 1942 looking like the war is going to take several years longer.

 

[tomo pauk]

The Army 20mm and the navy 25mm had similar problems. A low rate of fire and small ammo capacity. The Army 20mm was faster firing than the 25mm but even the best Army 20mm was around 2/3rds the rate of fire of the Oerlikon gun. The 'extra' range of the 25mm was largely an illusion due to crappy sights, heavy vibration when firing and large muzzle flash. But the 25m was large, heavy and did not traverse or elevate quickly so it didn't work well against short range targets either. Japan should had taken out a license for the Oerlikon FFS when they got the licnces for the Ff and FFL, at least they all use the same projectiles.

My opinion - that IJN should've skipped on the whole 25mm AA gun idea - is not a secret.
A 20mm gun have had the advantage that it can be plopped basically anywhere on the ship. A 2-, 3- or 4-barreled installation is also easily doable, the 4-barreled installation probably requiring the same size & weight allowance as a 37-40mm automatic?

get license for the Italian Breda 37mm AA gun? Modify it but keep the water cooling?

40mm Bofors exists before 1930, and it is still my 1st pick.
The 37mm Breda, or even the properly navalized 37mm Flak 18 will still give them much better service than the 25mm.

The Type 98 was a little too ambitious. 600 round barrel life? Dial back the velocity some and double the barrel life? Just need to keep the allied bombers honest. Make them fly higher than they would like/increase miss distances.

Yeah, do some play with propellant weight and/or shell weight, and it should've served them well.

Unfortunately the Japanese need twins because of distances. Whatever big singles they can build in 1944 are too late. They need to do a better job in 1942 and early 1943. They need to really STOP the allies in 1942 looking like the war is going to take several years longer.

Oh, yes, at least two-engined design, for the purposes of crew numbers required per A/C, other payload (bombs, fuel) and redundancy.
As a pure long-range ASW and recon platform, their take on the Catalina idea would've been fine.

 

[GrauGeist]

Oh, yes, at least two-engined design, for the purposes of crew numbers required per A/C, other payload (bombs, fuel) and redundancy.
As a pure long-range ASW and recon platform, their take on the Catalina idea would've been fine.

Thr IJN actually had a type that was comparable to the PBY-5, which was the Aichi H9A1.
It was originally intended to be a trainer and was built in low numbers (about 30 produced) with it's introduction being in 1942. At that point, it quickly went from trainer to coastal ASW duties. It wasn't fast or carried a warload even close to that of the H6K or H8K, but did have excellent range (which also means good loitering time over suspected targets near a convoy).

Sinve the H9A was already in production, the IJN certainly could have improved on that platform instead of waiting until the war was lost before introducing the Q1W.

 

[Shortround6]

My opinion - that IJN should've skipped on the whole 25mm AA gun idea - is not a secret.
A 20mm gun have had the advantage that it can be plopped basically anywhere on the ship. A 2-, 3- or 4-barreled installation is also easily doable, the 4-barreled installation probably requiring the same size & weight allowance as a 37-40mm automatic?

No disagreement on dropping the 25mm.
Japanese should had ditched 13mm or dropped it very early on.

A problem with some of these guns was the overly ambitious mountings. Maybe they OK when first designed/produced but aircraft design was advancing faster than gun/mount design and funding? Japanese test the 13mm guns in the early 30s, adopted it in Feb 1933 and got it into production in 1935.
US was using small numbers of .50 cal MGs and the British were using the .5in Vickers, mostly in a quad mount.
French and Japanese went a little overboard.

Four barrel unit was around 2600lbs but that is a bit deceptive as this thing needed a large crew. One pointer, one trainer, one sight setter and a number of loaders to deal with the 30 round magazines. Seven or more crewmen? And in a long engagement how far away were the ready ammunition lockers, where were the spare barrels and how long did it take to change them?
While the twin offered 1/2 the firepower it also was well under 1/2 the weight and used about 1/2 the crew.
The Japanese got this into production just about the same time they were asking the aircraft industry to start making monoplane attack aircraft. The large mount and complicated sight didn't actually add much to the effective range, which might have been OK against the B4Y biplane

not so good against the B5N that showed up in 1936/37.

Single barrel 20mm Oerlikons are a much better option than the 13mm and 25mm Hotchkiss guns.
Going past twin mounts for triples or quads may give diminishing returns. Even 20mm guns are going to start needing power elevation and traverse and reloading the center gun/s is going to be harder. And then there is the urge/desire to use better sights/fire control on the larger, heavier mounting.

40mm Bofors exists before 1930, and it is still my 1st pick.
The 37mm Breda, or even the properly navalized 37mm Flak 18 will still give them much better service than the 25mm.

The 37-40mm group of guns are a bit harder to judge. The Bofors was by far the best but there two different Bofors and a host of mountings.
Bofors came both air cooled and liquid cooled and came in simple had worked mountings, and powered mountings and in stabilized mountings.
Weight of mountings are all over the place
Type of mount and type of fire control could make a huge difference in effectiveness. In US service most of the quads and many of the twins had remote gun directors (although only a few meters away) to get the gun aimer off the mount and out of the smoke. US quads and twins were power operated and used liquid cooling.
Air cooled 40mm Bofors mounts with manual control are going to be a lot less effective although nowhere near as bad as the 25mm Hotchkiss.
British rarely used the 2pdr Pom Pom in single mount (or twins?) in it's modernized form. It lacked range but it had good destructive effect, a decent rate of fire, and was water cooled for long engagements.

 

[Shortround6]

Japanese had a Catalina type flying boat in development/production,
but it had problems.
The Yokosuka Y5Y1

Perhaps more effort could have been used?
Perhaps the specification was too ambitious?
They wanted the same range/speed as the 4 engine flying boat H6K1/2 using just two engines.