3 April 1948 — President Harry S. Truman signed the European Recovery Program proposed by Secretary of State George C. Marshall. The Marshall Plan was intended to stop the spread of Communism and restore the economies of European countries devastated by World War II. Over four years, the program distributed $12 billion to the nations of Western Europe.
4 April 1949 — Twelve nations signed the treaty creating NATO, the North Atlantic Treaty Organization, a common military alliance against the threat of expansion by the Soviet Union into Western Europe.
5 April 1986 — A bomb exploded at a popular discotheque frequented by American military personnel in West Berlin, killing two U.S. soldiers and a Turkish woman. American intelligence analysts attributed the attack to Muammar Qaddafi of Libya. Nine days later, President Ronald Reagan ordered a retaliatory air strike against Libya.
12 April 1961 — Russian cosmonaut Yuri Gagarin became the first human in space.
14 April 1986 – U.S. warplanes, on orders from President Ronald Reagan, bombed the Libyan cities of Tripoli and Benghazi in retaliation for the April 5th terrorist bombing of a discotheque in West Berlin.
17 April 1961 — The Bay of Pigs invasion of Cuba undertaken by a Central Intelligence Agency sponsored paramilitary brigade. The attempt to overthrow Premier Fidel Castro of Cuba failed.
20 April 1978 —A Korean Airlines commercial airliner traveling to Seoul was shot down over Soviet airspace and forced to make an emergency landing on a frozen lake near the Finnish border. The incident killed two of the 109 passengers and crew members aboard.
26 April 1986 — An explosion at the Chernobyl nuclear power plant in the Ukraine, caused a meltdown of the nuclear fuel and spread a radioactive cloud into the atmosphere. The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties.