Carl Feindt seems extremely knowledgeable on USOs, I think he's the top researcher of USOs, there's some great reading on his water UFO website about unknown objects submerging and emerging from our oceans...There are plenty of reports on the website, I have his book but have not read it completely... ....

I haven't read his book but I browsed his website years ago. Then I went back to Paul Hill's book to cross-reference their findings, and I was struck by the fact that Paul Hill had roughly characterized gravitational field propulsion years before it first appeared in the academic literature. In both sources I recall cases where a repulsive field was indicated below the craft, as the academic literature later described as half of the equation for gravitational propulsion, and Feindt's website also has cases where the water bulged above a submerged craft before it emerged, which seems to suggest a positive gravitational field above the craft, also as required for gravitational field propulsion. So the theory and the observations appear to match. And Paul Hill's book and other resources seem to indicate a resting mass of these craft in the range of a few tons, which appears to indicate that enormous masses aren't required to produce the field effects - somehow these craft can generate positive and negative gravitational fields without harnessing astronomical-scale mass-energies. Ergo, they're modifying the coupling constant between mass-energy and spacetime via some as-yet-undiscovered physical principle. So that's where we're stuck: we don't know how to do that yet. It's an unsolved problem in theoretical physics. And I see no way that we can find the solution in further examination of UFO reports, so there are only two possible paths forward: 1.) We could examine a sample of the technology that produces these gravitational field effects, and try to work backward to explain how they work by linking quantum field theory (QFT) with general relativity (GR) - and in fact we're already seeing a glimmer of a connection in the stress-energy tensor of photonic metamaterials. And/or: 2.) We can examine our theoretical physics models and try to build a mathematical bridge between QFT and GR since we can now see that it's possible, and ultimately, technologically accessible.

There is another book about UFOs and water, written by Russian author who worked as official CCCP Navy's researcher. after CCCP collapsed archives were open and he simply published previously classified material. Book is full of cases like: Soviet submarine surfaced in the middle of the ocean in the middle of the night, officers in the conning tower noticed 300m 900ft UFO rising from water, officers commanded whole 100 men crew onto top deck, officers and all sailors wrote and signed individual descriptions of the event (so nobody's calls anybody crazy) and upon return it was submitted to archives. Now US navy is about 10 times bigger and 10 times more active. By just simple scalling US Navy must had had 10 times more encounters than Soviet Navy.