Hi, John John:
They are paravanes, which are sort of like submarine kites, and they are towed fromt he vessel at a predetermined depth and angle as a way to ward off anchored mines and to cut the mines from their moorings. They ride out from the vessel by means of the wings, and if all works well the tow lines guide the mooring lines of mines into a toothed cutter on the paravane that then cuts the mine's wire, releasing the mine to the surface where it is disposed of, usually by gun fire.
Cheers!
Jim