"Active dipping sonar on display at the Pima Air & Space Museum, Tucson, AZ.

From the plaque: The AN/AQS-13 is a helicopter borne active dipping sonar used to detect and track submarines. They are lowered into the water on a cable from a hovering helicopter and can detect a target at ranges of up to about one mile. They are primarily used for final localization of targets that were initially found and tracked by other sensors.

The active sonar gives a very precise location for the targeted submarine, making it easier for the helicopter to drop its weapons accurately, and leaving the submarine with the smallest amount of time possible to react and attempt to evade the attack."