On 17 April 1961, Brigade 2506, a group of 1200 exiled Cubans led by CIA agents Grayston Lynch and William Roberson, invaded the Bay of Pigs, Cuba. Their goal: overthrow the feverishly anti-American Cuban government. The result: within 72 hours the invasion was crushed, humiliating the newly elected President Kennedy and heralded in Havana with chants of "Cuba Si Yankee No"
Described in the New York Post as the "mother of all American military and foreign-policy disasters" the botched invasion was not only operationally disastrous -- the intrepid Brigade 2506 was effectively abandoned by the Kennedy administration, which later had to pay $53m in food and medical supplies to have them returned -- but acted to escalate the tensions between the USSR and the United States, leading directly to the Cuban Missile Crisis in October 1962.
The decisive moment in the affair that came to be known as "the moment Kennedy blinked" occurred when Khrushchev wrote to Kennedy on 18 April 1961, pleading for JFK not to allow the "flame of war ignited by interventions in Cuba to grow into an incomparable conflagration". The Soviet Union, Khrushchev added in a foretaste of what was to come, "will render the Cuban people and their government all necessary help to repel an armed attack."
Embarrassed and desperate to regain credibility JFK instructed members of the National Security Council to provide another mission where he could prove his commitment to the fight against communism. Four years later, American troops were on the ground fighting in Vietnam.