Monday marks the 80th anniversary of the beginning of the Battle of Bzura - the largest and bloodiest of the German invasion of Poland in 1939.
On September 9, 1939, Polish forces, comprising the Pomeranian and Poznań Army, launched a surprise attack on the German units near the Bzura River to the west of Warsaw, who were moving towards Poland's capital city.
After initial successes by the Polish Army, the Germans regained control over the battlefield, putting Polish forces on the defensive. Outnumbered two to one, less well equipped and lacking ammunition and food, Polish forces began their struggle to break out from encirclement and retreat towards Warsaw.
Around 50,000 Polish soldiers managed to cross the Bzura River and continue towards Warsaw, while the other units were destroyed by the Germans. The Polish casualties amounted to 15,000 - 20,000 dead, 50,000 wounded and 100,000 captured.
The Polish attack slowed down the German march onward to Warsaw, but it could not change the course of the campaign. However, it was the largest ground offensive military operation launched against the Third Reich until 1941.