The thermocline offered submarines only a temporary acoustic refuge

Did Second World War navies understand the thermocline, and how did it affect anti-submarine warfare?

They understood it, but submarines still had to rise toward periscope depth to attack, limiting the protection the layer offered.

The thermocline could interfere with sound propagation and complicate sonar contact. Wartime navies knew of the phenomenon, although their ability to exploit or counter it was limited. A conventional submarine could not simply remain beneath the layer throughout an attack because it normally had to return to periscope depth. That operational requirement reduced the layer's value as a complete answer to Allied anti-submarine warfare.