On the night of 31 August 1939, the word 'blitzkrieg' was added to the dictionary. The German Luftwaffe was discharging incendiary bombs from the sky, while the Wehrmacht stormed the ground with heavy artillery. The Polish Army made a valiant effort, but they were outweighed in machinery, munitions, and manpower. By 14 September, the invading forces had them surrounded. There was no way out. The final defeat of Poland took place in a marshy area of the Bug River. The document of surrender was signed 6 October 1939. The Poles never accepted the term "Unconditional".