Throughout history, cats have always been involved on both sides of the conflict (usually because they want to see which side wins so they can rush over to that side and enjoy the spoils of war, such as more plentiful food).
At one time, the Belgium military tired to use cats like carrier pigeons to deliver messages, but the cats simply wandered off and the Belgium military cancelled the project. An Egyptian general reportedly even surrendered to avoid hurting cats that were roaming around the battlefield. Now if only people in Egypt still thought that way, we could stop the whole risk of civil war in that country by giving every Egyptian a cat.
Cats have also been favorites on naval ships, keeping sailors company while earning their keep keeping the ship free of mice and rats. For more information about cats during wartime, read more here.