11 September

Western Front

 * Pursuit of the Germans from the Marne: the French recover Épernay, Châlons, etc.

Eastern Front

 * Galicia: Russians close in on Grodek.

Southern Front

 * Serbia: Fierce battle with Austrian invaders at Krupani.

Naval and Overseas Operations

 * Bismarck Archipelago: Australian expedition captures Herbertshöhe.