Pigeons were one of the most impactful animals used in World War II.  While long-distance communication improved greatly around the time of the Second World War, militaries still employed the use of homing pigeons to carry life-or-death messages long distance.  The use of pigeons as messengers has been traced back for millennia, with the first documented use being the ancient Romans two thousand years ago.  In some terrains, the environment was too rough to use a radio to communicate, so the use of pigeons was employed.  Pigeons were also used more when the military was too close to enemy lines.  The pigeons carried their messages in little capsules attached to their legs.  This eventually changed to a capsule fastened to their backs, which allowed for a heavier load.  It took around eight weeks to train a pigeon to be able to deliver messages efficiently.  During this training, the bird built up stamina and started learning its aerial bearings.  Once trained, the pigeons would be sent off to deliver their messages before returning back to their camps.  Some pigeons actually became prisoners of war.  One pigeon was delayed in her return flight.  She arrived back with a note that said "To the American Troops: Herewith we return a pigeon to you. We have enough to eat. —The German Troops."