Read "Double Cross". Ben Mcintyre. many many pigeons released by the Brits with attached messages were never intended to be read by the brits. .................they were there to confuse the Germans.
The Brits even used known incompetent "homing" pigeons, hoping that they would fly to German pigeon lofts,as the Germans were paranoid about British pigeons infecting their perfect pigeons.
Not a lot of people know that, you know.