I was told in the bar at a wargames convention about an event that is supposed to have taken place on 7th June 1944, when suddenly the Allies lost all radio communication. There was a great deal of concern that the Germans had somehow managed to find a way to jam Allied signals, but this concern faded as communications where gradually restored over the next few hours and days (for smaller transmitters).
It is further said that the Germans lost all radio communication at the same time and were concerned that the Allies had found a way...etc.
So the story goes, the cause was later tracked down as a cosmic particle shower resulting from an X-ray burst event in the Andromeda galaxy.
I'd like to know: is there a speck of truth in any of this, and where I might find out more about it?