Khrushchev agreed on a deployment plan in May 1962, primarily in response to Castro's fears over yet another American invasion, and by late July, over 60 Soviet ships had been en route to Cuba, some of them which were carrying military material. A U-2 flight on the morning of October 14 photographed a series of surface-to-air missile sites being constructed. In a televised address on October 22, US President John F. Kennedy announced the discovery of the installations and proclaimed that any nuclear missile attack from Cuba would be regarded as an attack by the Soviet Union and would be responded to accordingly. Khrushchev sent letters to Kennedy on October 23 and 24 that claimed the deterrent nature of the missiles in Cuba and the peaceful intentions of the Soviet Union.