Some Unidentified submerged objects (USO) may be some kind of power plants.

All around the world, researchers work with things like waves- and other hydro-power solutions. In some cases, the wave power plant or the underwater hydropower plant can look like a saucer. Those saucers might involve turbogenerators that allow water to flow through them. The difference in pressure near the surface and deeper makes water flow through the plate. And that thing makes this system rotate the turbine wheel. These kinds of systems can deliver energy to any device that has access to that system's energy production. 

There are even underwater windmills that harvest energy from ocean currents. The underwater hydro plants can deliver energy to underwater drones or other robots. Those robots can used to repair underwater cables, or there could be computer centers in underwater positions. Water offers clean, green, and free energy to those bases. 

Those hydro plants can deliver energy to some underwater laboratories, or even highly classified military systems at the bottom of the oceans. In some visions, the missile bases can hidden on the ocean floor. There are underwater laboratories called "AUTEC" in Bahama. So there could be similar deeper sea facilities like the "Aquarius" base near Florida. 

Underwater power plants can used to operate automatized radars or other intelligence installations, anti-ballistic missiles (ABM), or research plants. 

The underwater plants can also create hydrogen, chlorine, and oxygen for propellants for the rockets that will launched from oceans. 

Those bases can be fully automatized drone bases. When those drones that are hidden secretly at the bottom of the sea get the order, they will rise to the surface or travel to the operational areas underwater. Then those quadcopters jump out from the water and begin their missions. That system can use remote-control technology to wake them up. 

https://futurism.com/search?q=Former+Naval+Officer+Raises+Alarm+About+%E2%80%9CWorld-Changing%E2%80%9D+Underwater+UFO+Captured+on+Video

https://en.wikipedia.org/wiki/Aquarius_Reef_Base

https://en.wikipedia.org/wiki/Unidentified_submerged_object

https://en.wikipedia.org/wiki/Atlantic_Undersea_Test_and_Evaluation_Center

Images: 

https://futurism.com/search?q=Former+Naval+Officer+Raises+Alarm+About+%E2%80%9CWorld-Changing%E2%80%9D+Underwater+UFO+Captured+on+Video

https://wonderfulengineering.com/this-new-technology-generates-electricity-and-potable-water-from-ocean-waves/