As early as August 1962, the US suspected the Soviets of building missile facilities in Cuba. During that month, its intelligence services gathered information about sightings by ground observers of Russian-built MiG-21 fighters and Il-28 light bombers. U-2 spyplanes found S-75 Dvina (NATO designation SA-2 ) surface-to-air missile sites at eight different locations. CIA director John A. McCone was suspicious. Sending antiaircraft missiles into Cuba, he reasoned, "made sense only if Moscow intended to use them to shield a base for ballistic missiles aimed at the United States."  On August 10, he wrote a memo to Kennedy in which he guessed that the Soviets were preparing to introduce ballistic missiles into Cuba.