Victory at Sea - Submarines Part I 

I was curious about the hedgehogs. I couldn't find them in the index. Are they explained under cruisers. I've yet to fully read this incredible book. Started with the starter set to make sure I was interested in the game. Then I noticed a bit in there about submarines and automatically bought the big rulebook. What an awesome game this is. I've always been a wargamer but haven't bought into a system like this since the 90's. Really fantastic. First time I saw Bolt Action a guy showed me his 250+ minis and dropped that book in my lap. Not the best intro. Automatically you feel way behind. Also my eyes are done painting those tiny guys. Thing was I have many more land games then sea games. Got around 8 of the older Avalon Hill naval games, but was thrilled to bring the collection more into the present.

So, how do you divide the board? When submerged, do you take away the model from the board?