WASHINGTON — Hours earlier an American U-2 spy plane had been shot down while snapping photos of nuclear missiles secretly placed by the Soviet Union in Cuba, just 90 miles from US shores. Despite a US naval blockade, Soviet cargo ships carrying more military supplies were steaming toward the Caribbean island.

It was Oct. 27, 1962, “the most difficult and tense time” of the Cuban missile crisis, Attorney General Robert F. Kennedy scribbled on a legal pad after huddling with his brother, President John F. Kennedy, and his closest advisers.