Not Nuke mines, that's a bit over the top probably.
And incredibly expensive to use.
New mines, something with a reasonable explosion but not too nasty.
You should be able to lay maybe 20 of them and a cruiser could get through it with maybe half hull damage (Hitting say, 15)
Also the ship wouldn't be able to hold that many of the mines, due to it's size.
So for use in real combat, it needs to be small.
Gunboat sized, maybe 20 mines and that's it.
