Underwater Alien Bases: The History of a Hidden-Ocean Theory

Stories of lights and objects entering or leaving the sea are almost as old as modern UFO reporting, but the specific theory of permanent undersea bases was set out by Ivan T. Sanderson, a Scottish-born naturalist, writer and broadcaster based in the United States. In Invisible Residents (1970), Sanderson collected maritime reports of strange lights, underwater objects and unexplained disappearances, and speculated that an intelligent civilisation, possibly non-human, might live under the oceans, which cover most of the planet and were then largely unexplored.

Sanderson’s ideas fed into the Bermuda Triangle craze of the 1970s, popularised by Charles Berlitz’s The Bermuda Triangle (1974), in which undersea intelligences were among the suggested explanations for lost ships and aircraft. In later decades UFO writers attached base claims to specific locations. Claims about Puerto Rico have circulated in local and online UFO lore, and the author Preston Dennett has written about reports he associates with a possible base in the Santa Catalina Channel off southern California, including sightings near Malibu.

Interest revived after 2017, when official acknowledgement of UAP reports brought new attention to objects seen over water. Some commentators, including a few former military and government figures, have spoken publicly about the importance of studying unidentified objects in the sea, and online discussion often links these remarks back to the older base theory.

Believers cite eyewitness reports from sailors, fishermen and coastal residents of lights rising from or descending into the water; sonar contacts reported in naval anecdotes to have moved at unusual speeds; and clusters of sightings in particular coastal areas. They argue that the deep ocean is poorly surveyed, so a base could exist without detection.

The quality of this evidence is low for the specific claim. Most reports are anecdotal and cannot be checked, and many of the naval sonar stories that circulate lack verifiable dates, ships or records. Clusters of sightings along coasts often coincide with busy shipping lanes, military exercise areas, airports and populated shores where more people are watching. None of the reports describes a base itself; the base is an inference drawn from lights and objects.

No navy, oceanographic agency or government has reported an undersea alien installation. The All-domain Anomaly Resolution Office’s 2024 historical review found no verifiable evidence of extraterrestrial technology. Modern naval forces monitor key ocean areas intensively with sonar arrays, and a large artificial structure or regular traffic of fast underwater craft would be difficult to conceal from them and from commercial and scientific surveys.

It is true that much of the seafloor has not been mapped in high resolution; the international Seabed 2030 project was set up precisely because of that gap. But oceanographers point out that lower-resolution mapping by satellite altimetry covers the whole ocean, and that unmapped detail does not mean unobserved activity. Sanderson’s 1970 case also predates most modern ocean monitoring.

Sceptics suggest ordinary explanations for the underlying sightings: flares, ship and aircraft lights, bioluminescence, reflections, rocket launches, military submarines and exercises, and atmospheric effects over water. Larry Kusche’s The Bermuda Triangle Mystery Solved (1975) showed that many disappearances cited by Triangle writers had been exaggerated, misdated or had known causes, which undermined one of the pillars of the undersea intelligence idea.

Believers answer that not every report fits these explanations, and that military secrecy may hide what navies have detected. They also note that humans have explored only a small fraction of the deep ocean in person. These points are fair as statements about uncertainty, but uncertainty about the deep sea is not positive evidence that anything artificial is there.