Looks like another torpedo physics bug. Niche, but these things can outrange bulkheads while being immune to surface weapons... doesn't seem fun to play against if you happened to build on the shore.
With a little luck, you can even outrange urchins, or harass other sea based structures/units with impunity.
You still want torpedos to bounce for coastal urchins to work. Maybe reduce their lifetime once they leave the water after entering it the first time? They still have to be able to chase fast boats.
Hopefully the dolphining fix in recent commits fixes it.