On this date in 1986, the worst nuclear reactor accident occurred in Chernobyl in the Soviet Union. An explosion and fire sent radioactivity into the air. At least 31 Soviets died immediately, and many more persons died from radiation poisoning.

On this date in 1961, about 1,500 C.I.A.-trained Cuban exiles launched a botched invasion of Cuba and failed to overthrow the government of Fidel Castro.

On this date in 1970, three years after N.A.S.A. let three Apollo 1 mission astronauts die,

its Apollo 13 mission was crippled by the explosion of a liquid-oxygen tank after four-fifths of the journey to Earth’s moon.