German U-Boat

U-boat beacons were simply communication devices which were used either as a place marker for a location or for transmitting messages.

Schwammboje (Swimming Beacon)

A simple device which transmitted a fixed frequency to other U-boats to indicate the location of a convoy. It entered service in late 1942 and continued to be used until mid-1944.

Fuhlungshalterboje (Contact Beacon)

This was a multi purpose beacon which could be used for general contact purposes. It consisted of a float, a cylinder with a flare inside and a timed fuse. The fuse was ignited before release, and could be set to burn for up to 30 minutes, at the end of which the flare ignited. The flare could release thick colored smoke or starburst lights.

Transmitting Beacon

As U-boats could not send or receive messages when submerged, an expendable beacon was developed which could hold a recorded message and would be released from a submerged U-boat. It consisted of a recorder, a transmitter and a delay switch housed in a watertight casing. The message would be recorded, and the beacon released, where it floated to the surface and transmitted the message after a preset delay. It sank itself once the message was transmitted.