We exploit the military mobilization for World War II to investigate the effects of female labor supply on the wage structure. The mobilization drew many women into the workforce permanently. But the impact was not uniform across states. In states with greater mobilization of men, women worked more after the war and in 1950, though not in 1940. These induced shifts in female labor supply lowered female and male wages and increased earnings inequality between high school--and college-educated men. It appears that at midcentury, women were closer substitutes for high school men than for those with lower skills.