Per an article on 8/22/2014 by Bruce Strauss: "Cats were a common sight in the trenches & aboard ships where they hunted mice & rats. Beyond thier 'official' duties, they were also embraced as mascots & pets by the soldiers & sailors with whom they served. An estimated 500,000 cats were dispatched to the trenches where they killed rats & mice; some were also used as gas detectors." THIS PIC IS: "A GUNNER WITH THE REGIMENTAL CAT IN A TRENCH. CAMBRIN, FRANCE, Feb 6, 1918 (IWM)"