Overview of Red Herring
This Radiolab archive story traces a bizarre Cold War-era Swedish naval mystery: for years, the Swedish military believed Soviet submarines were infiltrating its waters, triggered by a series of sightings and a secretive acoustic signal known as the “typical sound.” The twist is that the sound was eventually traced not to Soviet espionage, but to massive schools of herring releasing air bubbles underwater — turning a national security crisis into an accidental fish-fart joke.
The Cold War Panic in Sweden
- In the early 1980s, Sweden lived with intense fear of Soviet aggression across the Baltic Sea.
- The fear was sharpened in 1981, when a Soviet submarine ran aground near Sweden.
- Swedish authorities treated it as a major geopolitical incident, reinforcing the belief that Soviet subs were actively violating Swedish waters.
- After that, the military heavily increased coastal surveillance using:
- ships and nets
- helicopters
- hydrophones
- sonar-like acoustic monitoring
The “Typical Sound” and the Submarine Hunts
What the military thought it was hearing
- Repeated submarine alerts continued through the 1980s and into the 1990s.
- Reports often mentioned a mysterious underwater signal called the “typical sound.”
- This sound was classified for years and was treated as proof of Soviet submarine activity.
- Military personnel used it to justify escalating searches, including dropping depth charges in harbors and blockading exits with nets.
Why it became a national obsession
- The Soviet submarine threat fit the existing Cold War narrative.
- Once the military and politicians committed to the idea, the evidence was interpreted through that lens.
- The secrecy of the military system made it difficult to question the assumptions or test alternate explanations.
Magnus and Håkan’s Scientific Reinterpretation
- Magnus Wahlberg, an underwater acoustics expert, and his mentor Håkan Westerberg were brought into a secret government investigation in the mid-1990s.
- When they finally heard the classified “typical sound,” they immediately suspected it was biological, not mechanical.
- Their intuition: the sound resembled air bubbles underwater.
The fish hypothesis
- They focused on herring, which have a unique buoyancy mechanism:
- fish use a swim bladder to control depth
- herring can expel gas through a canal connected to their anal opening
- That expulsion can create a stream of bubbles, which underwater hydrophones can detect as a popping, squeaking sound.
The Experiment and the Reveal
- Magnus and Håkan tested the idea in increasingly elaborate ways:
- squeezing dead herring in a lab
- testing fish in water with a hydrophone
- finally observing wild herring schools in a fishing net
- The crucial breakthrough came when a large school of stressed herring produced the exact mysterious sound.
Final conclusion
- In 1999, it became official: the “typical sound” was not Soviet submarines.
- It was the sound of thousands of herring releasing air bubbles together.
Main Takeaways
- Confirmation bias can distort interpretation: once officials believed the sound meant “submarine,” they kept finding evidence for that conclusion.
- Secrecy can block scientific reasoning: the military’s top-down, classified structure made open debate and alternative explanations difficult.
- Nature can mimic threat: a biological sound pattern was mistaken for hostile military activity for more than a decade.
- Human systems are fallible: even high-stakes national security institutions can be led astray by incomplete data and assumptions.
Notable Insight
- The episode frames the whole affair as a kind of long-running, unintended joke on humanity: a global superpower scare, driven in part by herring.
- It also leaves a cautionary note about today’s world: future generations may one day laugh at our own confident misreadings the way we laugh at Sweden’s submarine panic now.