When the 8th Air Force bombing campaign began in 1942, there was no number of​ combat missions an airman was expected to complete before finishing his​ wartime tour of duty. Flight crews were required to fly until they died, shot down​ and became a prisoner of war, were seriously wounded and removed from flying​ status, or the war ended.

Crew and aircraft losses took a serious toll on the morale of combat crews and​ ground personnel. The medics were also encountering serious flight issues such​ as frostbite and anoxia at high altitudes; plus other medical problems including​ flying and combat fatigue and the physical and emotional stability of the men.

By early 1943 twenty of the 306th Bomb Group original flying crews and some​ replacements had been lost. 306th Flight Surgeon Maj Thurman Shuller wrote a​ letter to 8 th Bomber Commander General Ira Eaker, and requested a limit of 20​ combat missions be established after which an airman would be relieved of flying​ duties.

​Eaker agreed with Shuller but decided to establish ​the limit ​at 25 missions. This change​ gave flyers a goal ​to aim for and hope​ that they had a chance to ​return home to their loved ones.