Thread by @AshTheWiz

An interesting tale about submarines.
A Soviet submarine ran aground on Sweden's south coast very close to a Swedish naval base in 1981. They claimed it was due to an emergency and navigation errors, but Sweden took it as attempted snooping by the USSR in Swedish waters.
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The sub returned but Sweden was on alert, convinced that Russian subs could still be lurking off their coast. Soon they began to pick up elusive underwater signals & sounds. Swedish subs, patrol boats, and helicopters started pursuing them for over a decade but to no avail.
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Each time, the search would reveal nothing but a few bubbles on the sea surface. Sweden was worried about the intrusions but couldn't fathom why, would Russia provoke them since the Cold War was long over.
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In 1996, Magnus Wahlberg, a prof at the Univ of Southern Denmark, was included in the investigation of the strange signals. He was taken into a secret underground room in Bergen naval base Stockholm where the officers played those sounds, the first time ever for a civilian.
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He had expected it to sound like the sonar ping you hear in movies when a submarine is detected or the noise of a propeller. But as per him, it sounded like frying bacon or like small air bubbles releasing underwater.
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He began investigating with a colleague to trace the source that could be making bubbles on a scale that would make Sweden think it was dealing with a nuclear submarine.
Strangely, he found the solution in herring, a fish.
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Apparently, herring have a swim bladder which is connected to the anal duct of the fish, a feature, found only in herring. So a herring can squeeze its swim bladder, and let out a small number of bubbles through the anal opening. In simple words, they let one rip.
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Herrings swim in vast schools spanning several square kilometers and up to 20 meters deep. When something frightens them, they can generate a lot of gas. The Swedish Navy was scavenging the seas looking for Russian subs scaring the fish and then chasing the bubbles.
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To test his theory, Wahlberg bought a herring and applied pressure and it made a sound. He played the footage to the navy personnel who confirmed that was a perfect match for the noise they had been hearing.
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The good news was that Sweden wasn't under threat from Russia, the bad news was it had spent 10 years deploying its military in pursuit of fish farts. Since it figured out what was and wasn't fish farts, there have been zero reports of hostile intruders in Swedish waters.
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