17 October

Western Front

 * Herlies captured by the Allies: End of the offensive of the Allies.
 * Heavy German counter-attacks impose a strenuous defensive for a period extending to 17 November.

Eastern Front

 * Poland: Crisis of Battle of Warsaw: Russian reinforcements reach the city and save it from capture.

Naval and Overseas Operations

 * HMS Undaunted with accompanying destroyers sink four German destroyers off Dutch coast.