I thought some guys did a ton of testing and found that at that depth setting they detonated even if set to contact.
OK, found thread:
http://www.subsim.com/radioroom/showthread.php?t=118393
It's the switch, the magnetic does work, but the switch doesn't.
More here:
http://www.subsim.com/radioroom/showthread.php?t=118464
So I was wrong I guess. I tried to set the range of influence long in my mine mod---now I know how to addd stuff, I bet I can make tube-launched mines!
Another thing to try!
tater