*As the radio operator turned the bar, the direction-finding loop antenna on the bridge, topside, would turn and pick-up any radio signals.
*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 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 Gila