The Japanese set their depth charges according to what their average submarines were capable of--typically 250 foot dive depth. They assumed that US subs had the same capabilities. To admit that US Submarines were better than they believed would have been culturally incorrect at that time. I think most of this info can be found in Silent Victory by Clay Blair.
Germans: The U-boat crews had no idea they could go so deep when the war started. The test depth for basically all their subs was 90 meters. However, a prewar accident caused them to change that so they would not go below 50 meters--and they didn't until they actually got into combat. Proof for this is in almost all good books of the Battle of the Atlantic. Early encounters with enemy escorts and the U-Boats were trying to evade at depths of 90 meters or less illustrates that they did not know they could go deeper safely.
On the website
www.de220.com you can see a latewar teardrop depth charge. It has a setting for 900 feet. I've never found any difinitive info as to when the Allies changed depth settings but I do know they went from 300 to 450 to 600 and then 750. I'd never read about deeper seetings than that but there they are on a real depth charge...
Anyway, SH3 or SH4, I have fun evading them. That is unhistorical
. I've never talked to a WWII submariner that enjoyed being depth charged.
Cheers!!!