Focusing on the Second World War and early Cold War Era, this study uncovers how female activists promoted women's scientific participation as a shared solution to national security concerns. By appropriating the language and the cause of national defense, they presented powerful, sophisticated, and surprisingly familiar critiques of the pervasive cultural attitudes and discriminatory practices that discouraged women’s scientific interests and aspirations. Although these activists lacked the analytical tools to comprehend the deep-rootedness of women's scientific subordination, they still conceived of it as the product of social forces. They realized fully that women's exclusion stemmed from a series of cultural attitudes and deliberate choices regarding who could do science and who could not. But, in the context of the Second World War and early Cold War years when scientific brainpower was supposedly at a premium, they argued that this artificial and inaccurate distinction, along with all of its ramifications, was ultimately wasteful and unpatriotic. In an era that discouraged and even punished dissent, the language and cause of national defense provided activists with a culturally legitimated means for critiquing gender conventions and discrimination. The invocation of defense rhetoric, however, not only camouflaged but also compromised their agenda. Activists' own implorations to utilize female intellect and stem the waste of scientific talent elided their interest in sexual equality. The militaristic and technocratic language in which they couched their demands, moreover, subordinated women's rights to national needs and circumscribed their liberatory potential. Nevertheless, these efforts at expanding women's scientific participation are significant because they set the groundwork for later feminist reform. In effect, this study reveals that contemporary feminist interest in science did not spring full-blown from the so-called second wave of American feminism but rather, had been percolating for some time. Reclaiming this early history complicates our picture of the mid-twentieth century as an era of domestic complacency, illuminates continuities between earlier efforts and contemporary feminist critiques, and calls into question the waves of feminism paradigm.