I'm watching "Weird Wonders of the World" just for the heckuvit.

In this episode, we find the Swedish Navy... well, chasing a red herring.

During the Cold War, they laced the Baltic with microphones, in search of Soviet subs. These produced what was termed "the typical sound".

Only "the typical sound" did not stop. Sweden thought it had Russian subs plying its coasts.

They (finally) consulted marine acoustic engineers, and played the sound for them. (It's very staticky.)

But the engineers knew what was up.

Herring have an air bladder that is vented by the anus. They release air to disorient predators.

Yep, Russian subs = spooked herring!