Administratively, it was part of the Grodno-based III Military Corps Area and under Józef Olszyna-Wilczyński, it was also an important garrison and mobilization centre.

In the Interwar period, the city housed the entire 1st Legions Infantry Division, as well as the headquarters and the 4th Niemen Uhlan Regiment of the Wileńska Cavalry Brigade.

Air cover was provided by the majority of the Polish 5th Aviation Regiment [pl] stationed at the nearby airfield of Porubanek (modern Vilnius Airport).

The air assets were attached to the Modlin Army and the Narew Group fighting against the German units trying to break through from East Prussia.

The military commander of the city, Colonel Jarosław Okulicz-Kozaryn, decided that in case of attack by German or Soviet forces, he had insufficient forces for a successful defence and thus his task could only be to allow civilians to evacuate to neutral Lithuania (this was also realised, albeit not very clearly, by General Józef Olszyna-Wilczyński, commander of the III Military Corps Area which the city was also in).

On 18 September, the commander of the Belorussian Front, Komandarm (roughly a general), Mikhail Kovalyov, ordered that the city be captured by the 3rd and 11th Armies.

The 3rd Army delegated the 24th Cavalry Division and the 22nd and 25th Armoured Brigades under Kombrig (senior to colonel but junior to divisional commander), Pyotr Akhlyustin, to advance from the northeast and the 11th Army delegated the 36th Cavalry Division and the 6th Armoured Brigade under Kombrig Semyon Zybin to advance from the southeast.