The USS Miami nuclear submarine is 362 feet long, weighs 395 tons and is thrust by 35,000-horsepower engines. Yet the sound it radiates into the sea is little more than the hum of a kitchen refrigerator.

The ocean can be a noisy place: collapsing waves, rain, ships and marine animals (particularly snapping shrimp!) create quite a cacophony. The audio signatures generated by submarine machinery and propellers are distinct, however, and their propagation must be reduced profoundly so a sub can disappear into the background noise. Enemy forces are constantly listening with floating sonobuoys, sonar mines, passive arrays towed by ships and subs, as well as active sonar from those vessels.

This article was originally published with the title Deep Silence.

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