Prior to 1941, USAAF bombardiers could have been sergeants but after that time they, the pilot, co-pilot and navigator were all officers.
After selection, the cadet attended Bombardier School lasting 18 weeks. It consisted of 425 hours of ground instruction in the proficiencies of a bombardier (plus familiarity with the tasks of the pilot, radioman, or navigator in case of an emergency). After 3 weeks this included 120 hours of air training in which the cadet began with practice runs and ended by performing bombing runs with live ordnance. Upon graduation, he received a bombardier's wings and was entrusted with the Norden bombsight.
They were then transferred to an OTU to join a crew being trained for overseas duty.