I never researched what happens when playing at easy level as I have never played that level.
When I was found this out and was banging my head against the keyboard trying to figure out why the numbers were didn't add up I started a thread in the Tech Support section. At that time many thought that I was trying to lift up the Queen's skirts because I was detailing the information that I was finding. A couple of people, at the least - Pax Mondo I am pretty sure you were one of them - green-buttoned me for trying to pursue and understand this matter. AndyMac was ticked off because I was revealing top secret material in the eyes of the design team.
But now that some years have passed and the game has been out for many years I really feel that all should be aware of what actually happens. I never play at on anything except normal as I modify the scenarios I play in order to produce these extra needed points as is done in Ironman. I still keep track of the AI by using Tracker to monitor the Japanese economy, and should Japan be getting critically low on oil, fuel, supply, resources or HI, then I can switch to hard for a turn or two to boost the pools.
The AI seems to want to carry things away from Japan but does not like to carry materials to Japan and seems to have a real tendency to want to empty the pools and has no "sense of conservation". It appears to do a better job at getting fuel there than anything else, but many ships are carrying just a small portion of what they could carry and are therefore quite inefficient. That is why in the latter stages of game I have quit worrying about why I never spot very much Japanese shipping - because most of them spend the war sitting docked in ports. Now's the time to get your Pearl Harbor revenge urges satisfied.
This can be understood by all the comments you will find about how computer controlled task forces set up to automatically supply bases you want supplied does not work very well. It works even less well for the AI. Mull that over for a moment and you will clearly see the problem.
This is kind of contradicted by the game I played years ago as Allies vs. Japan.Played "historical" but I guess I also took it some times to "hard". Do not remember. However I remember the Japan islands weren´t short of anything they had masses of planes and stuff and units. I do not thin out of supply. I landed at Hokaido then jumped over to mainland... in early 44 or so. I noted that most city hexes were so full of stuff, that I just gave up the game as the further conquest would mean a boring and terrible battle of attrition. Just ship any div I can find over but I believe that still would not be enough. However I won this game as most Japan territory outside their mainislands was gone....ofc I note that this terrible battle of attrition I describe above would be the reality if history would different (without eg. firebombing and a-bombs)...
In this game vs. Japan the AI also seems to have no supply problems I find it takes ages that they run out. So I supected they get a bonus already on "historical". Fleets also get a bonus ie. they do not take damage if over their range. They practically have unlimted range (even if then on vlow speed perhaps)...this is helpfulfor the AI I am sure it would have troube handling correct task groups with different ranges.
My experience with stock scenario 6 (Dec 8 start) against the Japanese AI is similar to Alpha77's. Per suggestions from the forum, I played on Hard, until I found that I was capturing some large caches of supply in New Guinea, then I switched to Historical in mid-44, so I could effectively bypass and isolate island bases. I have been very conservative, since it is my first GC, and I suspended the sub campaign for much of '44 because of sub losses to the uber-E boats. I started bombing the HI from the Marianas in Jan '45, but scaled that back after major losses. Luckily, the AI is not great at the ground campaign, so I was able to implement an air/surface blockade on a line from Cam Ranh Bay to New Guinea in late '44.
It is now early Jan '46 and the HI have not received any convoys from the DEI in more than a year. I also control all of Manchuko and the entire Chinese coast (except Canton, Hong Kong, and Shanghai are blockaded). I've controlled all of Kyushu except for Nagasaki for the last month.
I just peaked at the Japanese side and found that Tokyo has more than 8M supply points. I restarted the B-29 campaign from China, with the 8th AF and Bomber Command pitching in from Korea, but I had to undertake 3 months of massive fighter sweeps from Okinawa and Korea and sustain heavy P-51H and P-47N losses before I was able to whittle down the HI fighter defenses.
I don't use Tracker, but from peaking at the Japanese side, the AI seems to run a pretty good economy.