im pretty sure submarines are getting a huge buff and sea mines are going to be a hassle for submariners not only will they be easily spotted if they're near the surface i would just be in the way for submariners

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Sea mines would have to be a piloted craft to work and defies most of what consists as a craft. If you want a sea mine try to use skulks underwater and connect them with a dispenser and tnt underneath the sand. If someone is fighting above the area the sea mine can detonate and blow up under them.