The Old Naval hearing Base, unlike the old cannon bases, is the only naval jurisdiction (boat is under army jurisdiction) on the island. From the sound detector under the sea, observers watched out the screw sounds that passed through the Kitan Strait on a 24-hour system. It was a place to detect the enemies submarines sound as soon as possible. At that time, it was said that about thirty people were working in three shifts, and cooking facilities and living facilities such as toilets also remein.