Homing pigeons were used by both the Axis and the Allies to carry messages in WWII. They both used them to carry information, and it made it hard for the other side to capture the messages.
200,000 homing pigeons were given to the British military by European citizens. They were trained by the National Pigeon Service to create a secret and fast delivery system. The United States supplied tens of thousands of pigeons as well.
The most famous American pigeon was named G.I. Joe. He worked for British soldiers. G.I. Joe flew 25 miles in 25 minutes to let the Americans know that their bombers were headed to a town that the British troops had taken over. Joe saved the day and the lives of the soldiers in the town. He was awarded the Dickin Medal of Gallantry by the Lord Mayor of London for his work.