NOOB 2

[peterloo]

Most of the players here do play reaistic, but I'm one of the exception. I don't use TDC as I don't like the trigo behind it. I play v1.2 + Die Slowly stage 16. I'm always thinking that they DDs in v1.3 are overdosed and unrealistic. So if you want to play easily, install v1.2 patch, after gathering experience after 1~2 career, consider updating to v1.3

Ok. Back to the topic.

First, you've to ensure that you're not touching the sea bottom. Send a ping to check depth below keel if you're NOT chased by any DD.
Secondly, some early war subs like the Sugar boat (S-class) CANNOT withstand pressure when going to deep (>120m / 400ft). Others like Gato don't have this problem.
Finally, to pull the boat up, use Blow Ballast command. Blow it for several times to ensure that the boat will rise. WARNING: If chased by DD, prepare for a gunnary duel. If a cruiser is near you, YOU WILL PROBABLY DIE. You may consider AHEAD FLANK after reaching surface ,man the desk guns to wand them off, and change direction / speed often, head to nearest U.S. naval base, hoping that the tin cans will break off attack / get destroyed BEFORE you do. Use torpedoes as "sniping weapon" like what you see in U-571. (U-571 definitely sucks as it is very inaccurate. But I'm just quoting a possible tactice that you may employ)