The Polish Military Organisation (POW) was a Polish nationalist secret military organization which was founded in August 1914 by Jozef Pilsudski. It merged two youth paramilitary organizations and served as the intelligence and sabotage arm of Pilsudski's Polish Legions during World War I, initially focusing on activities in central Poland before expanding to all parts of the former Poland-Lithuania, including Lithuania, Belarus, Ukraine, and Russia. After Poland was occupied by the Central Powers in 1915, the POW became a semi-legal organization which was unofficially supported by the Imperial German Army. However, after the July 1917 Oath Crisis, the POW returned to being an underground operation and took part in covert actions against German and Austro-Hungarian garrisons and supply lines. In December 1918, following its service at the Battle of Lemberg, the POW was merged into the Polish Army, but the POW remained active in Ukraine even after the Polish Army withdrew from Kyiv in July 1920 during the Polish-Soviet War. The POW also took part in the Greater Poland uprising of 1918-1919 against Germany, as well as in the 1919-1921 Silesian Uprisings; after the success of the first revolt and the failure of the latter ones, the POW in German territory was incorporated into the Polish Army. The POW also attempted to overthrow the government of Lithuania, and Poland acquired the Sejny region through a POW-instigated uprising. The POW dissolved in 1921, but the Soviet NKVD charged and imprisoned or executed accused POW members during the Great Purge of the 1930s.