How many Polaris submarines were enough?

How many Polaris submarines would provide a sufficient deterrent?

Burke argued for at least forty boats with sixteen missiles each, enough to guarantee sixteen at sea and probably sustain about twenty if worked hard. That meant 256 to about 320 missiles on patrol.

The reported question put to Burke was how much of a Polaris force would be enough. Forty boats, each carrying sixteen missiles, could guarantee sixteen at sea; keeping about twenty on patrol required working them hard. Those patrol strengths meant 256 or about 320 missiles at sea. Early submarine-launched ballistic missiles were considered second-strike weapons because of their accuracy limits. Their survivability meant that vulnerable bombers and land-based missiles did not have to remain on such a high launch-on-warning alert, reducing the risk of an accidental war. Burke maintained this force-size argument through the Eisenhower and Kennedy administrations and before successive defense committees.