I like the mod so far.
Started a new campaign with U-4 and by the end of November had acquired a type VII boat.

But there is a definite bug I'm experiencing.
I can't sink ships with explosives or the ship engineer skill that nullifies the need for explosives.

Since your mod is the only one, I'm using, that alters the skill sets of officers, it seems to be related to this mod.

I also use some mods to extend the crew size, like "Crew mod [Extended]" which also increases the time a type VII can stay submerged to 20 hours, but your mod overwrites this.

My crew currently consists of 28 sailors and 8 officers and the oxygen only lasts for about 7.5 hours before modifiers. Even with blue light, its only slightly less than 9 hours.

This time frame is way too short.

A type VII would have oxygen for about 24 hours, under normal conditions, and the time could be extended by utilizing oxygen saving methods, like sending the non-essential crew to the bunks.

I think that should be reflected by the mod.
Especially, when you consider later war years, when the u-boats have to stay submerged for longer periods of time, because they are extensively hunted. 7.5 or less than 9 hours could be really stretching it, under such circumstances.
I did a test, and with blue light and 30 potassium absorbers, I could only stretch it to about 23 hours.
I would suggest to increase the time before the oxygen runs out. Maybe to at least 16 hours before any modifiers.

There might be some other minor conflicts with crew mods.
But I've encountered nothing game breaking so far.

Getting an error with the TypeIIA, where the torpedo tube management menu can't be interacted with as the sub is 'under water' despite being surfaced.

The problem with the broken "ship engineer" skill still persists.

I have it on a leader and on an engineer. Neither can sink ships with that skill.
Explosives seem to work, though.