The demands of combat require infantry troops to form strong emotional relationships based on trust and mutual dependence, to become a “band of brothers,” in the historian Stephen Ambrose’s phrase. At various points in U.S. history, military leaders and civilian defense officials have relied on that fact to resist the integration of African Americans, gays, and women into the infantry, arguing that their presence would disrupt the bonding process. In each case, the demands of maintaining an all-volunteer army, along with rapid changes in social mores, rendered that resistance futile: all three groups are now part of the American fighting force. MacKenzie confronts the main arguments offered by opponents of allowing women to fight, including women’s supposed physical weakness and emotionalism and the concern that sexual tension between male and female fighters would lead to problems. She does not deny that the presence of women will change the character of the infantry but argues that it might be a net benefit. This is a vigorous contribution to the debate on women in the armed forces, although there is some tension between MacKenzie’s demonstration that women can cope perfectly well with the demands of combat and her distaste for the militarism and nationalism that she associates with preparations for combat.