Final answer:
Robert McNamara served as the Secretary of Defense under President John F. Kennedy, shaping crucial military policies during the Cold War.
Step-by-step explanation:
Robert McNamara held the position of Secretary of Defense in President John F. Kennedy's administration. McNamara was a crucial figure during this period, advocating for the strategy of flexible response as opposed to mutually assured destruction. This defense strategy aimed to provide the United States with a range of responses to different levels of military conflict. As Secretary of Defense, McNamara's role was pivotal in shaping U.S. military policy and responses during the Cold War era, particularly in the context of the Cuba and Vietnam situations.