[R-390] BPL used during WWII?

[Harry Joel]

The ongoing discussion of BPL and its ramifications has intrigued me much. It appears that the German equivalent (up to a point) of Homeland Security had designed installed a warning system used during pending bombing attacks by Allied airforces near the end of WWII. I have seen this system in operation, but must admit that I have little information about what frequencies were used. As all AM (no FM back then) stations went off the air to prevent them to be used as beacons with RDF equipment aboard the bombers and Pathfinders (ahead of the bomber squadrons) civilians had no early warning system about what to expect and take to shelters as needed. 
The system transmitted voice messages via power lines to anyone using a free decoder box placed near an AM receiver. The decoder box received voice data from the wall outlet. A map came with the decoder box. The alerts always refered to a set of co-ordinates on these maps wich covered a few hundred miles in each direction from home base.
A typical transmission would go like this: 
"Approximate 400 planes in A-5 heading southwest" and may be a shortly after
"Turning  west and entering B-4"
Quite often these alerts kept track of more than one array of bombers. The turns were often an attempt to disguise the ultimate target.
I have done a Google search but could not locate any reference to this early BPL system used by the Germans.
I also read the info on http://www.arrl.org/tis/info/HTML/plc/bpl-deployment.html
to gain some insight for a possible comparison.