How did the United States discover that nuclear missiles were being installed into Cuba?

Question

They decoded a secret message from Fidel Castro
Pictures from a U-2 Spy plane
US spies in Russia found out
Cuban exiles smuggled secret documents into the United States With help from the United Kingdom spy network

Answer 1

The United States discovered that nuclear missiles were being installed in Cuba primarily through pictures from a U-2 spy plane. On October 14, 1962, a U-2 reconnaissance flight captured photographic evidence of Soviet missile installations in Cuba, which initiated the Cuban Missile Crisis.