Short answers, pulled from the story.
The Soviet Union detonated its first atomic bomb on the 29th of August 1949. The West named this device First Lightning, which was more or less a copy of Fat Man, one of the bombs dropped on Japan in 1945.
Operation Crossroads involved 95 ships including German and Japanese vessels captured during World War II. One plutonium implosion-type bomb detonated over the fleet while another exploded underwater.
Hungarian-American nuclear physicist Edward Teller led the Ivy Mike project that detonated the first hydrogen bomb on the 1st of November 1952. This explosion created a cloud wide and high enough to kill all life on surrounding islands.
The United Kingdom became the third nation to test a nuclear weapon when it detonated an atomic bomb in Operation Hurricane on the 3rd of October 1952. France became the fourth nation to possess nuclear weapons on the 13th of February 1960 when its atomic bomb Gerboise Bleue detonated in Algeria.
An American spy plane discovered nuclear missile sites under construction in Cuba on the 14th of October 1962. President Kennedy ordered U.S. military forces to DEFCON 3 then later to DEFCON 2 as tensions increased during this crisis.