Final answer:
In response to a counterforce nuclear strategy by an enemy, maintaining a strong second-strike capability is reasonable, which underpins the MAD doctrine, ensuring both sides avoid starting a nuclear conflict. Additionally, adopting a Flexible Response strategy with conventional force build-up allows for a more varied and proportionate response to military aggressions.
Step-by-step explanation:
A reasonable response to an enemy following a counterforce nuclear strategy against you would be to maintain a strong second-strike capability. This implies the ability to launch a significant number of nuclear weapons in retaliation, even after a severe first strike. During the Cold War, the United States developed its nuclear deterrent with mass stockpiles of nuclear weapons, ensuring that any first strike would result in Mutually Assured Destruction (MAD). The MAD doctrine was meant to deter both sides from initiating a nuclear conflict due to the certainty of mutual annihilation.
Aside from MAD, President Kennedy introduced a policy of Flexible Response, which built up conventional forces to provide the United States with more tactical options in the event of a conflict. This strategic approach allowed for a proportionate and varied response to different levels of military aggression, including potential small insurgencies or diplomatic crises, without immediately resorting to nuclear retaliation.