Anders commanded the Nowogródzka Cavalry Brigade during the German Army's invasion of Poland in September 1939 and was immediately called into action, taking part in the Battle of Mława. After the collapse of the Polish Northern Front the brigade withdrew towards Warsaw, and also fought heavy battles against the Germans around Minsk Mazowiecki and in the second phase of the Battle of Tomaszów Lubelski. After learning about the Soviet invasion of Poland, Anders retreated south in the direction of Lwów (now called Lviv), hoping to reach the Hungarian or Romanian border, but was intercepted by Soviet forces and captured on 29 September, after being wounded twice.