Section III : On means of injuring the enemy - Art. 21.
Art. 21. Belligerents may lay mines in their territorial waters and in those of the enemy.
But it is forbidden, even in territorial waters:
(1) To lay unanchored automatic contact mines unless they are so constructed as to become harmless one hour at most after the person who laid them ceases to control them;
(2) To lay anchored automatic contact mines which do not become harmless as soon as they have broken loose from their moorings.