An international crisis involving the USA and the Soviet Union. It was precipitated when US leaders learned that Soviet missiles with nuclear warheads capable of reaching the USA were being secretly installed in Cuba. President Kennedy reinforced the US naval base at Guantanamo, ordered a naval blockade against Soviet military shipments to Cuba, and demanded that the Soviet Union remove its missiles and bases from the island. There seemed a real danger of nuclear war as the rival forces were placed on full alert, and the crisis sharpened as Soviet merchant vessels thought to be carrying missiles approached the island and the blockading US forces. However, the Soviet ships were ordered by Khrushchev to turn back, and the Soviet Union agreed to US demands to dismantle the rocket bases in return for a US pledge not to attack Cuba. An outcome of the crisis was the establishment of a direct, exclusive line of communication (the ‘hot line’) to be used in an emergency, between the President of the USA and the leader of the Soviet Union.