The fall of the fortified area of Wizna upon the Narew River, the so-called Polish Thermopylae, and the suicide death of a heroic officer, Cpt. Władysław Raginis. The positions are attacked by the 19th Army Corps under the command of the well-known theoretician and practitioner of the art of war, Gen. Heinz Guderian.
The Polish troops advancing over the Bzura crush the German 30 Infantry Division, taking approx. 1,000 German POWs and seizing a number of towns (including Łęczyca).