In July 1962, Soviet Premier Nikita Khrushchev struck a deal with Fidel Castro to deploy nuclear-armed ballistic missiles on the island of Cuba. Over the next three months, the Soviets commenced work on nine launch sites, hoping to complete construction before the United States could discover them. In early September, Soviet SS-4 missiles began arriving in Cuba. However, US intelligence detected the bases before they could be completed, prompting the most serious nuclear standoff in history. After thirteen tense days in October, the Soviets agreed to remove their missiles in exchange for the withdrawal of US nuclear missiles deployed in Turkey and southern Italy. The most significant crisis of the nuclear age was thus triggered—and resolved—by foreign-deployed nuclear weapons.