15th "Greater Poland" Infantry Division (Polish: 15 Wielkopolska Dywizja Piechoty) was a unit of the Polish Army in the interbellum period. Founded on February 17, 1920, it was based on the 2nd Greater Poland Rifles Division. It actively participated in the Polish-Soviet War, including the Battle of Warsaw. After Polish victory, the Division chased the Red Army out of Mazovia, from the area of Łomża and Mińsk Mazowiecki.
After the conflict, the Division was stationed in Bydgoszcz, with one regiment in nearby Inowrocław. It was commanded by General Wladyslaw Jung (1920), General Wiktor Thommee (1924 - 1926 and 1928 - 1934), and General Zdzislaw Wincenty Przyjalkowski, during the Polish September Campaign.
In August 1939, with prospect of war growing, the Division was ordered to defend southwestern sector of the Polish Corridor between Bydgoszcz and Naklo. Backed by some field fortifications and located along the Brda, it successfully defended attacks of the 50th Infantry Division and the Netze Brigade of the Wehrmacht between September 1 and 2. Its rear units, remaining in Bydgoszcz, took part in the Bloody Sunday (1939), on September 3.
On the same day, the Division was ordered to retreat towards the Bzura and the Bydgoszcz Canal. Then, it withdrew to Toruń, continually attacked by the Wehrmacht and the Luftwaffe. Between September 9 and 18, the unit took part in the Battle of the Bzura, covering rear areas of Polish troops. After its defeat, the Division gathered around Palmiry, with 1500 soldiers still alive. Without heavy equipment, and after several skirmishes with the Germans, the remains managed to reach Warsaw on September 23 (see: Siege of Warsaw (1939)).
The 15th Infantry Division was reformed in the Polish People's Army after the war (see pl:15 Dywizja Piechoty (LWP)).