assumed that his only option was to prepare the country for nuclear war, which he personally thought had a one-in-five chance of occurring. In the weeks immediately following the Vienna summit, more than 20,000 people fled from East Berlin to the western sector, reacting to statements from the U.S.S.R. Kennedy began intensive meetings on the Berlin issue, where Dean Acheson took the lead in recommending a military buildup alongside NATO allies. In a July 1961 speech, Kennedy announced his decision to add $3.25 billion (equivalent to $ billion in ) to the defense budget, along with over 200,000 additional troops, stating that an attack on West Berlin would be taken as an attack on the U.S. The speech received an 85% approval rating. A month later, both the Soviet Union and East Berlin began blocking any further passage of East Germans into West Berlin and erected barbed wire fences, which were quickly upgraded to the Berlin Wall, around the city. Kennedy's initial reaction was to ignore this, as long as free access from the West to West Berlin continued. This course was altered when West Berliners had lost confidence in the defense of their position by the United States. Kennedy sent Vice President Johnson and Lucius D. Clay, along with a host of military personnel, in convoy through East Germany, including Soviet-armed checkpoints, to demonstrate the continued commitment of the U.S. to West Berlin. Kennedy gave a speech at Saint Anselm College on May 5, 1960, regarding America's conduct in the emerging Cold War. His address detailed how he felt American foreign policy should be conducted towards African nations, noting a hint of support for modern African nationalism by saying, "For we, too, founded a new nation on revolt from colonial rule." Cuba and the Bay of Pigs Invasion The Eisenhower administration had created a plan to overthrow Fidel Castro's regime in Cuba. Led by the Central Intelligence Agency (CIA), with help from the U.S. military, the plan was for an invasion of Cuba by a counter-revolutionary insurgency composed of U.S.-trained, anti-Castro Cuban exiles led by CIA paramilitary officers. The intention was to invade Cuba and instigate an uprising among the Cuban people, hoping to remove Castro from power. Kennedy approved the final invasion plan on April 4, 1961. The Bay of Pigs Invasion began on April 17, 1961. Fifteen hundred U.S.-trained Cubans, dubbed Brigade 2506, landed on the island.