I just recently go back into SHIII and can confirm all this after spending the last six weeks of playing time with the IIA and D
Even with all the problems I sunk 120,000 tonnes in an inferior boat
Slow on the surface is useless unless you are trying to slow down to let a merchant pass in front of you.
In smooth seas without engine upgrades 1/3 will get you 7 knots
I use 1/3 98% of the time since its the best combination of speed and fuel usuage
If you use 1/3 there is no reason you can't sail to Aberdeen or even north of Scotland and make it back
Just be careful when using standerd,full and flank
1/3 should be your default cruising speed in any boat
The periscope depth is indeed a pain in the ass
10 meters leaves the top of the tower poking out and its even worse in rough seas.
It took me a while to figure out how I was being seen at periscope depth until I went to external view and saw that my tower was causing a wake and the radio atenea was sticking out about .5 of a meter
The depth changes also took me a while to figure out
If you have your boat running at slow, depth changes will never happen.
You need to run at least 1/3 for them to happen
This really sucks when under attack or trying to avoid detection since running 1/3 greatly enhances your chances of being seen.
Try 1/3 and see if you can change your depth
The the GWX creators are reading this
Once change that I reccomend is for Type II boats to have a new defualt periscope depth of 12 or 13 meters
You can still use the periscope at this depth and everything is under water
So as someone who has mastered the Type II
Hopefully some of this will help
Its Feb of 1942 in my game and I am in 1st Flotilla so I have a Type II D now which is a massive improvement since I can afford to be picky about my targets since I have 320% more fuel
Next month I get a Type VIIC and I fear the game will become too easy
The mod is excellent and turns SHIII from a very good game to a legendary game
My one complaint is that you guys have ruined SH4 for me
I am German so I dont know much about US Navy subs
I bought the game and have tried playing it but just cant get into it. I miss the open endedness and extras of GWX

SH4 feels sooooo restricted
Not very many bases, limited start dates etc etc
But the subs are interesting (and lavish!, German subs are 29 dollar a night motels and US subs are 5 star resorts) and the graphics are incredible
So maybe if you guys have the energy you can convert alot of the ideas from GWX into the new game and create a super mod for that game
Thanks for all your effort. I wish I could do something more than say thank you since that sound very hollow after all the hard work.
And sorry if any of this is unreadable. My English is still bad