If you use TDWs UI mod - then you do not need this one and the snorkel within the ui mod has to be added using the options editor.
This MUST be done in the bunker (not in your uboat) as it will ctd if not.
As it will add an item to your boat - you must be careful about using old saves (where snorkel was not added) as you will ctd.
So best bet is to use the UI mod and read up on how to use the options editor
