Hey, if the oceanographic ship was putting out its Notices to Mariners then I'd expect that those were not U.S. submarines!One or two "eels"-hydrophone strings- lost, usually when a submarine snagged the "eel" towed a mile or two behind the ship)...
Whales don't give off 60-hertz tonals & harmonics, either... or were those 50-hertz tonals?Subs were easy to pick up and distinguish from whales.