Temperature layers in water can hide submarines from sonar.

Evidence

Refraction can also occur at the boundaries between liq­ uids at different temperatures, such as water, and in some cases the level of refraction can result in total internal reflection. This effect is sometimes used by submarines to hide from the sonar of other ships; it can also cause the sound to be ducted between two boundaries and in these cases sound can cover large distances. — David Howard, Jamie Angus, coustics and Psychoacoustics, 332

Categorization

• CANDY: Submarines exploiting acoustic refraction to vanish from sonar is a vivid, shareable tidbit.
• corroborated: 2 independent passages support this claim — David Howard, Jamie Angus, coustics and Psychoacoustics, 332
• XREF: connects to: Temperature inversion layers refract sound away and create silent zones; Deep-ocean pressure and temperature trade-offs create a sound-speed minimum waveguide; Cold water layers create a natural acoustic amphitheater — Gordon Hempton, John Grossmann, One Square Inch of Silence- One Man’s…, 241

Broader Connections

• Temperature inversion layers refract sound away and create silent zones #expands (0.95)
• Deep-ocean pressure and temperature trade-offs create a sound-speed minimum waveguide #expands (0.85)
• Cold water layers create a natural acoustic amphitheater #corroborates (0.80) — Gordon Hempton, John Grossmann, One Square Inch of Silence- One Man’s…, 241