AK, Armia Krajowa
The Armia Krajowa (the Home Army), was the dominant Polish resistance movement in World War II German-occupied Poland. It was formed in February 1942 from Związek Walki Zbrojnej (Union for Armed Struggle) and over the next two years incorporated most other Polish underground forces. It was disbanded in January 1945, when Polish territory had largely been cleared of German forces by the advancing Soviet Red Army.
Armia Krajowa, with over 400,000 members, was by far the largest Polish underground resistance movement, and the world's second largest after the Yugoslav Partisans. It constituted the armed wing of what became known as the "Polish Secret State".
AK's primary activity was sabotage of German transports headed for the eastern front in the Soviet Union. AK also fought some full-scale battles against the Germans, particularly in 1943 and 1944 during "Operation Tempest”, thereby tying down a number of German Army divisions.
Armia Krajowa, loyal to the Polish Government in Exile, was viewed by the Soviet Union as an antagonistic force, leading to growing conflicts between AK and Soviet forces both during and after the war.