Dipping sonar evolved from earlier experiments

When did dipping sonar appear?

Helicopter dipping sonar was tested in the 1960s, while shipborne lowered-sonar experiments date back to the Second World War.

Familiar helicopter dipping-sonar trials date to roughly the 1960s. An older method used cranes to lower sonar into the water from ships. Second World War experiments already sought to place a sensor below thermal layers that interfered with detection. The helicopter made the technique mobile and tactically flexible, but it did not invent the underlying idea of lowering the sonar beneath a difficult layer.