Make sure u chose deep ocean regions only

+ block access through engl straight and engl coast line

+ enough fuel 24/7

yeah, I did all that too...

Submarines are in a stage where we are looking for optimal balance and have their stats changed very regularly atm.
Afaik in vanilla Subs are the meta I understand, ofc in TW we strive for a proper/historical balance, so don't expect they are as op as in vanilla.

If you want to have your subs as OP as possible, you'll need
-Up to date tech on every slot and a decent amount of doctrine
-Location: with deep sea tiles and out of reach of planes
-Mass: ideally around 4 per pack.

Most important to know is: Subs get relatively more powerful towards the later techs.

Tech 1 or 2 will suffer given enemies screens they start off with are still relatively efficient against them.
Having sub tech 3 or 4, ideally ahead of time (through Nfs often possible) in large enough numbers will have a very good kill/death ratio to convoys and even take out some outdated screens along the way.
Hope this helps!

thanks for the detail, but if you want to make it historical then the subs at the start of the war should be very powerful as the tech to hunt and destroy them was not well develop at the time. It should be hard to detect and destroy them in 1939 and 1940 and after that both AI and human player should be able to research better sonar/radar and anti sub weapon tech. the way it works right now is the complete reverse.

- Until you research snorkel tier 2 your subs gets spotted way too easily.
- I have lost way more subs in the early part of the war and the longer the war goes on the easier it gets for my subs, where historically it was the contrary.
- Researching every sub tech of 1939 will give you catastrophic result.
- Only after researching all the 1940 sub tech it gets easy.

Basically I think the balance should be the other way around. Subs strong in early war, but weak at the end if the enemy have researched and equipped the 1941-1943 sonar/radar and anti sub weapon. The subs tech for post 1941 should just help to keep the subs relevant not make it overpower.

why do subs have radar only slots instead of sonar?
thats something that kinda required for a sub to detect other subs