See resource for October 18, 1962 for brief description of the Cuban Missile crisis and October 18 & 19 resources for timeline up to this date.
Saturday, October 20: Under the public guise of an "upper respiratory infection," President Kennedy returns to Washington from Chicago after being convinced by Robert Kennedy that he must meet again with EX-COMM to discuss, among other things, the discovery of additional Soviet missiles in Cuba.
Sunday, October 21: After learning that an air strike against the missile sites could result in 10-20 thousand casualties, and that another U-2 flight discovered bombers and cruise missile sites along Cuba's northern shores, President Kennedy decides on a naval blockade of Cuba. When confronted with questions regarding rumors of offensive weapons in Cuba, Kennedy asks the press not to report the story until after he address the American public.
Monday, October 22: Despite being urged by Senate leaders to call for air strikes, President Kennedy addresses the American public and announces his resolve to implement naval blockade only. U.S. military alert is set at DEFCON 3 and Castro mobilizes all of Cuba's military forces.
Tuesday, October 23: The Organization of American States unanimously supports the U.S. decision to quarantine Cuba and, by the end of the day, all naval vessels are in place. Stunning reconnaissance photos reveal that Soviet missiles are poised for launch.