Soviet repressions of Polish citizens occurred as well over this period. Since Poland's conscription system required every nonexempt university graduate to become a military reserve officer, the NKVD was able to round up a significant portion of the Polish educated class as prisoners of war. According to estimates by the Institute of National Remembrance (IPN), roughly 320,000 Polish citizens were deported to the Soviet Union (this figure is questioned by some other historians, who hold to older estimates of about 700,000–1,000,000). IPN estimates the number of Polish citizens who died under Soviet rule during World War II at 150,000 (a revision of older estimates of up to 500,000). Of the group of 12,000 Poles sent to Dalstroy camp (near Kolyma) in 1940–1941, mostly POWs, only 583 men survived; they were released in 1942 to join the Polish Armed Forces in the East. According to Tadeusz Piotrowski, "during the war and after 1944, 570,387 Polish citizens had been subjected to some form of Soviet political repression". As early as 19 September, the head of the NKVD, Lavrentiy Beria, ordered the secret police to create the Main Administration for Affairs of Prisoners of War and Internees to manage Polish prisoners. The NKVD took custody of Polish prisoners from the Red Army, and proceeded to organise a network of reception centres and transit camps, and to arrange rail transport to prisoner-of-war camps in the western USSR. The largest camps were at Kozelsk (Optina Monastery), Ostashkov (Stolobny Island on Lake Seliger near Ostashkov), and Starobelsk. Other camps were at Jukhnovo (rail station "Babynino"), Yuzhe (Talitsy), rail station "Tyotkino" ( from Putyvl), Kozelshchyna, Oranki, Vologda (rail station "Zaonikeevo"), and Gryazovets.