What is the schnelltauchback?
 

Ok, I think I am going to try this mod, and I know what this boat looks like. But for the life of me, I dont know why this exists? I seached uboat.net, wiki, but it gives limited information. Why do these boats look like this?

The purpose of the cutaway deck shape was to make the U-Boat submerge faster by about ten to fifteen seconds. Which, with the skies full of aircraft made a critical difference. Presumably by using the weight of the water in the cutaway area to pivot the bows at a steeper angle.

That makes sense since these are type IXC used later when air cover was greatest. Thanks!

So I finally got my type IXC and I have used the Schnelltauchback mod. This is a pretty good mod. The few less seconds to dive is a blessing around the British isles! And it looks cool too. Awesome job!