But, even though this topic may not deserve its own acronym, it certainly was prime fodder for a few cable television documentaries (see my playlist above.)
The USO concept should be a no-brainer for those people who buy into the existence of UFOs. Think about it, if aliens are traveling across the vast cosmos to visit Earth, where do they stay once they get here? Some of these beings might be lucky enough to book a room at Area 51, but what about the economy travelers? With 7 billion locals scurrying around this planet, the only option for these road-weary little green guys is to grab some real estate on the ocean floor.
I never had a problem imagining ET crews getting some shut eye in the Atlantic before continuing their journey to the next star system. This theory accounts for the occasional sightings. For the record, however, it took lots of introspection before I was ready to consider the existence of entire underwater alien bases or cities on Earth.
Initially I posed this question to myself: How could an underwater base even exist unless the aliens had a facility on land to manufacture it? After all, you can’t build a submarine underwater. Then, one day, I saw a mobile home commercial and I realized a plausible answer existed to my question. These bases could be manufactured on other planets, and transported to Earth’s oceans. And, just like the mobile home commercial had described as common practice for purchased double-wides, these aliens could be transporting pre-manufactured structures to our ocean floors and assembling them onsite.
As I grew to accept the possibility that our pristine ocean floors may in fact be sprawling alien trailer parks, a disturbing question came to mind. Are these seafaring aliens abducting our cattle because they get tired of seafood?
Christopher Columbus: On his maiden voyage to America, Columbus wrote in his journal about seeing lights underwater as well as in the sky that he could not explain. Read more.
US Navy: In 1963, a US Navy submarine’s sonar detected an unknown object off the coast of Puerto Rico. It was moving at 150 knots, 20,000 feet below the surface. The submarine monitored the USO for 4 days. For reference, today’s nuclear-powered submarines can barely hit 25 knots and can’t submerge deeper than 800 feet.
Shag Harbor: This is the mother of all USO incidents. It occurred at Shag Harbour, Nova Scotia in 1967. Several residents reported a 60 foot long object splashing into the local harbor. A panic followed because authorities assumed it might be an airplane. Local fishing boats, the Coast Guard and US Navy divers searched for survivors. Military assets were deployed upon the scene and no wreckage was ever officially reported. From this point, the story has developed many endings. Read more.
Norwegian Navy: November 1972, the Norwegian Navy located an unknown submerged object. They assembled several ships and sub-hunter helicopters to track the object, fearing it was an enemy submarine. After two days of pursuit, the giant cigar shaped object rose out of the water for 60 seconds. The Nords fired upon it and it disappeared back into the water without a trace.
At least some of the many recorded USO cases might be explained by unknown military technology or naturally occurring phenomena. Here are a few examples:
weirdtwist 
