Additional thoughts about the recent reporting:

https://www.nytimes.com/2017/12/16/us/politics/unidentified-flying-object-navy.html

From the article:

Then, Commander Fravor looked down to the sea. It was calm that day, but the waves were breaking over something that was just below the surface. Whatever it was, it was big enough to cause the sea to churn.

Analysis: Well, it’s fairly obvious that we (the United States) is engaged in underwater construction activities and that these activities are associated with the UFO phenomenon.

Specifically: It would be possible to construct HUGE aircraft and spacecraft on the seafloor, away from the prying eyes of satellite surveillance. These modular structures way too large to build in standard hangars without the danger of public exposure. The modules could be built on land and then transported to the ocean, where they would be welded together.

When completed, these vehicles could simply be lofted into space during the cover of night. The result: instant space stations far more sophisticated than anything constructed with conventional methods.

At any rate, it’s all in Flying Saucers.