LifeBoats&Debris v.4 from Rubini is a good mod. Also from Rubini Flags Enlighten.
TMT.mod
OLC Gold "MkII" from onelifecrises. However, quite difficult to plan your target. Or from H. Sie (hsGUI v3[1].1.rar)
Decks Awash (your U-Boat) will dive a little (7 meters) and your watch crew will stay on the bridge ... good mod too.
There are over 100.000 mods, just look at Jimbuna's image on the link that I wrote before. You will see his image and certain mods.