i'd think russians, germans or israelis to be more likely but don't see why any would reveal an advanced technology just to spy on training missions...
Most of the incidents have been at the Navy's practice/test ranges off the East and West coasts. In general, I think what they saw were simple technology like balloons with radar reflectors, other non-high tech drones, and stuff like that, just to "tickle" a response out of US systems. There are probably sensors deployed alongside those drones that receive information about radar bands and the like and transmit it back to whoever "daddy" is. All of that stuff is fairly easy to deploy from an autonomous device the size of a torpedo (or multiple devices like that). There are autonomous submersibles today that use air flasks to control their buoyancy and can "fly" hundreds of miles through the water just using buoyancy and aircraft like wings. They are essentially silent and are pretty cheap, and could certainly be used to deploy espionage devices and to stick an antenna above the waves to capture information about US technical means. Being that these areas are (generally) international waters, there's not much the US can do to prevent it.
Going a little deeper, I'd love to get a *real* expert to put very specific questions to the pilot interviewed on 60 minutes. I'd ask about the claim that the Tic-Tac went from ground level to over 60K' and back in a very short time, for instance. I'd love to know where he got that information. I don't think his F-18's radar could track something like that (using the circa 2004 radar he had at his disposal), and I know he can't measure that kind of thing with his eyeballs. So, did someone sitting behind a radar console on a nearby ship tell him that? Regardless, RADAR can be spoofed or the guy who told him that may not have first hand facts at his disposal. That video has been public domain for a while and nothing about it looks different (to me) than what it looks like when you see a balloon out of an aircraft's window. Even the videos with a cloud background appear to show the same kind of relative motion as what you'd see looking at a balloon out of the window of a nearby or circling aircraft.
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