USOs are Unidentified Submerged Objects. These objects have been caught on sonar and radar by the navies of different countries in the world. They have also been sighted during the submerging in and emering from the water. An interesting detail is that most of these sightings take place around Puerto Rico and the Dominican Republic, countries that lie at the border of the Bermuda Triangle. Could it be that on the bottom of the ocean there is an underwaterbase, however weird that may sound?

Anywany, this documentary is very interesting and worthwhile: