A common misconception (that may never go away) is that 25 missions was the magic number that would have a crewman whisked away back to the USA. Not at all true. There was no set number of missions a crew had to fly to be sent home. It was left to each Air Force's commanders in the field to determine when their crews had had enough, which was dictated by various factors including, more than anything else, the availability of replacement crews.
As the war progressed, many commanding officers began to raise the required number from 25 to 30, then to 35, and even to 50 in the Pacific Theater. As it was felt that mission dangers had diminished sufficiently and a crewman's chances of survival had increased enough, the number of required missions would routinely be bumped up accordingly.
Another common misconception is that crews were assigned to a particular aircraft, which is not at all true. Crews were assigned to a squadron and flew whatever plane was available for that day. Whenever possible, a squadron commander would try to keep a particular crew in the same plane, but really only for the sake of morale. Plus, a crew would take much better care of a plane they felt they "owned."
Most commanders would allow a crew to give their bomber a name and even to have nose art painted on it, again for the sake of morale. Crews were often disheartened when "their" plane was heavily damaged or lost when flown that day by another crew. Many bomb groups gave responsibility and stewardship of aircraft to the Ground Crew Chiefs to assign names and even paint nose art on "their" bombers, sometimes while consulting with the crews that considered them to be "theirs" and sometimes not.
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