[hyperion2206]

Originally Posted by klh

I believe it is the Balkon Gerät, a type of listening device fitted late in the war.

http://www.msichicago.org/exhibit/U5...lectronic.html

The U534 has one also. http://uboat.net/gallery/index.html?...534A&img=3

Somewhere I saw a closeup shot, but I can't seem to find it now.

Kevin

Balkon Gerät, that's the name I was looking for! I agree that it has to be that device.