Classic cases of group think -Bay of Pigs invasion (1959-1962)

Another closely-studied case of groupthink is the 1961 Bay of Pigs Invasion. The main idea of the Bay of Pigs invasion was to train a group of Cuban exiles to invade Cuba and spark a revolution against Fidel Castro's communist regime.

The plan was fatally flawed from the beginning, but none of Presendent Kennedy's top advisers spoke out against the plan. Kennedy’s advisers also had the main characteristics of groupthink; they had all been educated in the country's top universities, causing them to become a very cohesive group. They were also all afraid of speaking out against the plan, because they did not want to upset the president. The President's brother, Robert Kennedy, took on the role of a "mind guard", telling dissenters that it was a waste of their time, because the President had already made up his mind.

(Source: http://en.wikipedia.org/wiki/Groupthink)