John F. Kennedy's foreign policy was dominated by American confrontations with the Soviet Union, manifested by proxy contests. Like Truman and Eisenhower, Kennedy supported containment to stop the spread of Communism. President Eisenhower's New Look policy had emphasized the use of less expensive nuclear weapons to deter Soviet aggression by threatening massive nuclear attacks on all of the Soviet Union. Nuclear weapons were much cheaper than maintaining a large standing army, so Eisenhower cut conventional forces to save money. Kennedy implemented a new strategy known as flexible response. This strategy relied on conventional arms to achieve limited goals. As part of this policy, Kennedy expanded the United States special operations forces, elite military units that could fight unconventionally in various conflicts. Kennedy hoped that the flexible response strategy would allow the US to counter Soviet influence without resorting to nuclear war.

To support his new strategy, Kennedy ordered a massive increase in defense spending. He sought, and Congress provided, a rapid build-up of the nuclear arsenal to restore the lost superiority over the Soviet Union—he claimed in 1960 that Eisenhower had lost it because of excessive concern with budget deficits. In his inaugural address, Kennedy promised "to bear any burden" in the defense of liberty, and he repeatedly asked for increases in military spending and authorization of new weapons systems. From 1961 to 1964 the number of nuclear weapons increased by 50 percent, as did the number of B-52 bombers to deliver them. The new ICBM force grew from 63 intercontinental ballistic missiles to 424. He authorized 23 new Polaris submarines, each of which carried 16 nuclear missiles. He called on cities to prepare fallout shelters for nuclear war. In contrast to Eisenhower's warning about the perils of the military–industrial complex, Kennedy focused on arms buildup.