Stop that Pigeon!
Seriously though, Pigeons have been used to carry orders and secret documments since the 1871 during the Franco-Prussian War when messages were sent by the surround French forces. WW1 & 2 saw the increased use of homing pigeons as special units were set up by all the forces involved as pigeons are hard to detect, very difficult to shoot down, and fast commuters.
In 1903, a German Engineer, Julius Neubronner attached a combined tiny analogue camera and mechanical timer to a pigeon's neck and Spy Pigeon was born!
See the wing tips in the corners of these classified "spy pigeon" recce pitures