Vickers E, 7-TP and R-35 and 6 TK-3 and TKS tankettes). On September 8 the Commander-in-Chief, Marshal Edward Rydz-Śmigły ordered the creation of an improvised Warsaw Army (Armia Warszawa) under General Juliusz Rómmel. The newly created force was composed of the forces defending Warsaw and Modlin Fortress, as well as all Polish units defending the Narew and the Vistula between Warsaw and Pilica river lines. General Czuma continued to be the commander of the Warsaw Defence Force, which he split into two sectors: East (Praga district) under Lt.Col. Julian Janowski and West under Colonel Marian Porwit. The Army Poznań commanded by General Tadeusz Kutrzeba, and Army Pomorze under General Władysław Bortnowski started an offensive on the left flank of the German forces advancing towards Warsaw. As a result of this offensive that later became known as the Battle of Bzura, German commanders withdrew the 4th Panzer Division and sent it to counter the Polish threat near Kutno. Its positions were replaced by forces of a weakened German 31st Infantry Division. In this sense the desperate attempt to buy time for organising a defence of Warsaw was a success. The defenders of the city were joined by various units of the routed Prusy Army. In addition, several new units were created in Warsaw out of reserve centres of Warsaw-based 8th Polish Infantry Division and 36th "Academic Legion" Infantry Regiment. On September 11 the Polish Commander in Chief ordered that Warsaw was to be defended at all costs, despite the possible heavy casualties and civilian losses. The following day the forces of German 3rd Army (under General Georg von Küchler) broke through Polish lines along the Narew river and started its march southwards to cut off Warsaw from the east. It was assaulted by cavalry units under Władysław Anders, but after heavy fighting the Polish counter-offensive failed and the forces were withdrawn to the south. Other Polish units fighting under General Juliusz Zulauf near the Narew River area retreated and reached Warsaw on September 14. They were incorporated as the core of the defence forces of the borough of Praga district. On September 15 the German forces reached Warsaw from the east and the capital of Poland was under siege. Only a strip of land along the Vistula leading towards the Kampinos Forest and Modlin Fortress was still controlled by Polish forces. The defence of the Modlin fortress was an important relief