In late August 1939 the regiment, commanded by Colonel Kazimierz Burczak, was concentrated in forests between the Bug River and the Narew, as part of 1st Legions Infantry Division (General Wincenty Kowalski), Operational Group Wyszków.
In the night of September 4/5, 1939, the regiment marched towards Różan, where it was engaged in first clashes with the advancing Wehrmacht.