Question

In shifting to a defense policy based upon the concept of “flexible response,” President Kennedy was indicating that he had grave doubts about the value of which previous defense policy?

Answer 1

Massive retaliation, which was something of an "all or nothing" threat.

It was based on retaliating with the threat of such incredibly devastating force that the enemy had no choice but to back down. However, as the USSR improved its nukes and rocket technology, Kennedy preferred an approach that was more flexible to meet the changing nature of any threat with plenty of options as opposed to going all out at the first sign of trouble.