[##:##] Command : mine <SHIP> <NUMBER>
This command drops mines in the sea and is functional from ships with mine-laying capability (see info Ship-types).
See info Hitchance for the chance of a ship hitting a mine.
In the command syntax <SHIP> is the number of one of your ships and <NUMBER> is the number of mines you wish to drop. That number of shells, (assuming you've got them), will be dropped in the sector that ship occupies, magically becoming mines as they hit the water.
Mines can only be removed safely by a minesweeper. (Other ships can remove them by hitting them, but...) Planes with the 'sweep' ability can clear mines by flying recon missions through mined sectors, with each passage through the sector possibly removing some mines.
Ships of tech 310 or higher can detect mines with their sonar. See info sonar for more information.
Note that the sector is checked for possible mine hits only when a ship moves into it; thus, a ship may safely drop mines in a sector and then move out. On the other hand, the mines know no allegiance, so moving back into a mined sector is foolish at best.
Building a bridge clears all mines there.
You cannot drop sea mines into a harbor, only land mines.