A left-over from WW1, I guess....
That is what they expect us to believe. :-)
Sure it could be a WW1 left-over, but what if it is not? What if someone recently dumped a mine there?
I think I might have mentioned it before, but way back in the beginning with the Cleito talks about naval disarmament, I was thinking about pushing forward a plan to ban mines (and would have included a proper search for any lost mines). Somehow it slipped my mind and I never proposed it...
... looking at it now, perhaps I should have proposed it...