During World War I, messages were sometimes transmitted by wire (telegraph of field phone), but two-way radio communications had not yet become available. Sometimes a unit was ordered to attack over a broad and often difficult terrain, making it impossible to string the wire necessary for communications. In these situations, a field commander often carried with him several carrier pigeons.
Pigeons served many purposes during the war, racing through the skies with airplanes, or even being fitted with cameras to take pictures of enemy positions. But one of the most important roles they served it was as messengers. An important message could be written on a piece of paper, then that paper neatly folded and secured in a small canister attached to a pigeon's leg. Once the pigeon was released, it would try to fly to its home back behind the lines, where the message would be read and transmitted to the proper military planners.