It all depends upon what you would like to do. There are mods out there right now such as:
GWX3 Additional Ammo by Jimbuna
http://www.subsim.com/radioroom/down...?do=file&id=31
GWX3 All Weather Guns by Jimbuna lets you use the guns in heavy seas
http://www.subsim.com/radioroom/down...?do=file&id=32
Real DC-1 by Jungman reduces the damage distance for depth charges, so you can be DCed for hours and still escape
http://www.subsim.com/radioroom/down...o=file&id=3173
These may fit your bill. The additional ammo and all weather guns change cfg files in the Submarine and Basic folders under the Data folder. You can edit these using notepad. What did you want to with the torpedo's?