A rejection letter written in 1938 to a young woman applying for a creative position at Walt Disney serves as a reminder of the casual nature of socially accepted discrimination against female workers. The letter states that "women do not do any of the creative work in connection with preparing the cartoons for the screen, as that work is performed entirely by young men. For this reason girls are not considered for the training school."
Almost an exact version of it was sent to Frances Brewer in 1939, although on significantly less-cool letterhead.
It’s not that Disney didn’t employ women. It employed lots of them as "inkers" who corrected and filled animations, and worked in physically separate environments from the more prestigious male animators. In this video, you can see how the studio separated "creative" animation from inking:
But inking is just another part of the animation process — at times a grueling one, as Vanity Fair profiled in 2010. The segregation of work was doomed to fail, in part because of war. In 1941, the studio began training female employees to animate, and in a speech, Walt Disney told employees why. Note that Disney calls the adult women employees "girls":
The girls are being trained for inbetweens for very good reasons. The first is, to make them more versatile, so that the peak loads of inbetweening and inking can be handled. Believe me when I say that the more versatile our organization is, the more beneficial it is to the employees, for it assures steady employment for the employee, as well as steady production turnover for the Studio.
The second reason is that the possibility of a war, let alone the peacetime conscription, may take many of our young men now employed, and especially many of the young applicants. I believe that if there is to be a business for these young men to come back to after the war, it must be maintained during the war. The girls can help here.
Third, the girl artists have the right to expect the same chances for advancement as men, and I honestly believe that they may eventually contribute something to this business that men never would or could. In the present group that are training for inbetweens there are definite prospects, and a good example is to mention the work of Ethel Kulsar and Sylvia Holland on "The Nutcracker Suite," and little Retta Scott, of whom you will hear more when you see Bambi.
It's easy to forget that tragic events like war can, at times, yield positive social benefits, but the need for a reliable pool of workers seems to have pushed Walt Disney to allow women to "contribute something to this business that men never could or would." But don't take the historic changes in training to mean there's no longer a need or room for progress — Disney had its first woman film director in 2013 (Frozen).