Top 5: Cuban Missile Crisis facts 

It marked the only time the U.S. military was placed on DEFCON2, the next step to nuclear war.

AP file photoPresident John F. Kennedy, right, confers with his brother, Attorney General Robert Kennedy, during the October 1962 Cuban Missile Crisis.

Tuesday marks the 50th anniversary of the start of the Cuban Missile Crisis, an event that nearly triggered a nuclear war.

Here are five facts about the crisis: 
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– The Belfer Center at Harvard estimated there would have been 100 million U.S. and 100 million Soviet casualties in a nuclear exchange.

– The Joint Chiefs of Staff unsuccessfully advocated a full-scale attack and invasion of Cuba.

– The U.S. military was placed on DEFCON2, the next step to nuclear war on Oct. 22, 1962.

– The Soviet Union withdrew its missiles from Cuba in exchange for a U.S. public commitment not to invade Cuba and a secret pledge to withdraw missiles from Turkey.

– As a result of the crisis, a direct phone line from the White House to the Kremlin was established.