You can have a snorkel at anytime by enabling it in TDW's Options File Editor Viewer.
It is the first tab in the OFEV.
See my tutorial post #6
Also includes the download link.
Link to my SH3 – SH4 – SH5 posts:
Step By Step Tutorials & How To Do It.
Also Included Are Some Useful Download Links
http://www.subsim.com/radioroom/showthread.php?t=211804
You can use TDW’Generic File Patcher with STEAM see my Tutorial Post #125