A Bombardier School was a United States Army Air Forces facility that used bombing ranges for training aircrew. After ground simulator training with the Norden bombsight, the 12- to 18-week course recorded each student's scores for approximately 160 practice bomb drops of "Bomb Dummy Units" (BDU), both in daytime and at night. The elimination rate was 12%, and graduates transferred to a Second or Third Air Force training unit to join a crew being trained for overseas duty. The bombardier trainer used was the Beech AT-11 Kansan. With the increase in Eighth Air Force aircrews needed for the Combined Bomber Offensive, the 17 Army Air Forces Bombardier Schools graduated 47,236.