Comment Re:These are not the droids you're looking for (Score 1) 275
As best I've been able to find(on page 753 of The Naval Institute Guide to World Naval Weapon Systems) the unit cost of a Mark-46 torpedo alone is $160,000(in what I think are 1988 dollars; but it isn't entirely clear). Even if the launch cage is free, I suspect that nobody is planting nearly enough of them to be a major hazard to civilian life...
I assume that this is what keeps naval mines (mostly) out of the line of fire against land mines, which are absurdly cheap by comparison.