There are several underwater TTA's that have recently been found using Google Earth. Arecibo, and other underwater installations near the coastal islands of the Baja California Peninsula, and also at the Poles. Rev Michelle Hopkins has shown several TTA sites that have been located and observed.
Check out revmichellehopkin's recent videos on her YouTube channel. She's out in front with a lot of this info right now. A tenuous position. Helping to piece together information from many sources.