The first consignment of SS-3 MRBMs (medium range ballistic missiles) arrived on the night of September 8, followed by a second on September 16. The Soviets were building nine sites — six for SS-4s and three for SS-5s with a 4,000 kilometer-range (2,400 statute miles). The planned arsenal was forty launchers, a 70% increase in first strike capacity. The Cuban populace readily noticed it, with over one thousand reports reaching Miami, which U.S. intelligence considered spurious.
On October 7, Cuban President Osvaldo Dorticós (1959-1976) spoke at the U.N. General Assembly: "If ... we are attacked, we will defend ourselves. I repeat, we have sufficient means with which to defend ourselves; we have indeed our inevitable weapons, the weapons, which we would have preferred not to acquire, and which we do not wish to employ". Several unrelated problems meant the missiles were not discovered by the U.S. until an October 14 Lockheed U-2 flight showed the construction of an SS-4 site at San Cristóbal, Pinar del Río Province, in western Cuba.