5 September

Western Front

 * Retirement of British and French forces ceases.
 * Battle of the Ourcq (Maunoury's 6th Army) begins at mid-day.
 * Reims and Pont-à-Mousson occupied by the Germans.

Eastern Front

 * Poland: Austrians defeated by Russians at Tomashov.

Naval and Overseas Operations

 * East Africa: Germans attack Abercorn.
 * HMS Pathfinder sunk by German submarine.
 * Wilson liner Runo blown up by a mine.

Political

 * Agreement of London: Great Britain, France, and Russia pledge themselves to make no separate peace.