In that era, many young women loved not dresses but uniforms, and joined the army of their own will.
Tips
history
From Mao Zedong's (毛泽东) 1961 poem 《为女民兵题照》 ('Inscription for a Photo of Women Militia'): 飒爽英姿五尺枪,曙光初照演兵场。中华儿女多奇志,不爱红装爱武装 - 'Gallant, five-foot rifles in hand; first dawn lights the drill ground. China's daughters have striking ambition: they love not red finery but martial dress.' A signature line of Cultural-Revolution-era women's imagery.
usage
红装 = traditional red wedding/festive clothing; 武装 = military equipment/uniform. The couplet turns on the wordplay 红装 / 武装. Still frequently quoted, often playfully, about women in non-traditional roles.