On September 7, 1939, the division, commanded by Colonel Jarosław Szafran, was sent to the area south of Białystok, where it waited for train transports to move it westwards.

On the next day, it manned western line of defence of the city, and on September 15, it attacked the advancing Wehrmacht in Kortumowa Gora and Holosko.

The attack began in the afternoon, and by evening, Polish forces captured complex of a sanatorium along the road to Brzuchowice.

On September 19, Polish defenders of Lwów found out about forces of General Kazimierz Sosnkowski, which tried to break into the city from forests in the area of Jaworów.

After initial success, Poles were repelled by German tanks, and failed to aid General Sosnkowski.