*As the radio operator turned the bar, the direction-finding loop antenna on the bridge, topside, would turn and pick-up any radio signals.  The antenna was hoisted by compressed air.
*If the radio operator heard a foreign signal or beacon, he would look at his gyro-compass to find the relative direction from the U-boat to the newly acquired signal.

*The signal could be a beacon from another U-boat that had spotted a convoy and was forming a "wolfpack" of other U-boats to move in for the attack.

*The direction-finding loop antenna in this photograph is authentic.  The bicycle, ironing board, and sweater belong to my fabulous technical editor, Dieter Blumenthal.  Bicycles and ironing boards were not standard issue aboard U-boats.

Photo by Bruce Culp
Photo by kind permission of Dieter and his lovely wife, Gila