The Polish 1st Tadeusz Kościuszko Infantry Division (Polish: 1 Polska Dywizja Piechoty im. Tadeusza Kościuszki) was an infantry division in the Soviet-organized Polish armed forces (as opposed to the existing Anders Army) formed in 1943 and named for the Polish and American revolutionary Tadeusz Kościuszko. It was the first division formed of the First Army (Berling Army), and of what later became the post-war Polish Armed Forces (Ludowe Wojsko Polskie) after defeating the Nazi regime and its collaborators and liberating Poland.
An infantry division, it was formed in May 1943 in Sielce (near the Oka River) under the command of general Zygmunt Berling. It was organised according to the Shtat (Table of Organisation and Equipment) of a Red Army Guards Rifle Division, with minor amendments. In accordance with a decision of Joseph Stalin, Col. Zygmunt Berling took over the command of the division. Political control of the division was held by the Union of Polish Patriots. On July 15, 1943, the anniversary of the Battle of Grunwald, the soldiers of the division took the military oath. The oath sworn obligated, amongst other things Confidentiality of fidelity to the alliance to the Soviet Union and adherence to the brotherhood of arms [of the] allied Red Army. In late August shortages still existed – 20% of the standard complement of officers were missing and 36% of NCOs.
In June 1943, Commander in Chief and Prime Minister General Sikorski declared Berling's army as a communist Polish division, subversive, and its author as a traitor, a deserter from the Polish Army.