United States aerial reconnaissance of the Soviet Union Background . Beginning in 1946 , United States Army Air Forces conducted aerial reconnaissance flights along the borders of the Soviet Union and its satellite states in order to determine the size , composition , and disposition of Soviet forces . The necessity of peacetime overflights was reinforced after the escalation of the Cold War in the late 1940s and , in particular , after the Korea War started in 1950 . US President Harry S . Truman authorized selected overflights of the Soviet Union in order to determine the status of its air forces . It was feared that the Soviets might launch a surprise aerial attack on the United States with long - range bombers . First flights . In 1952 a modified B - 47B bomber made the first deep - penetration U . S . overflight of Soviet territory to photograph Soviet bombers in Siberia . ( Limited coastal overflights had been conducted by aircraft from the US Air Force and the US Navy several months earlier . ) This mission established that the Soviets were not massing bombers in eastern Siberia . Overflights of the Soviet Union with the newly designated RB - 47E s continued through 1954 , often at great risk , as they were routinely intercepted by Soviet MiGs . It became apparent that a new aircraft was needed that could operate at altitudes well above any Soviet air defenses . U - 2 missions . In November 1954 , President Dwight D . Eisenhower approved a secret program under the direction of the CIA to build and fly a special - purpose high - altitude reconnaissance aircraft named Project AQUATONE . Lockheed was chosen to build the reconnaissance plane and in August 1955 the first Lockheed U - 2 was test - flown . Other strategic reconnaissance missions continued as the U - 2 tests were ongoing . In early 1956 Project GENETRIX involved using high - altitude photo - reconnaissance balloons that were intended to collect photographic intelligence as they drifted across the Soviet Union . During Project HOMERUN ( between March and May 1956 ) RB - 47E reconnaissance aircraft flew almost daily flights over the North Pole to photograph and gather electronic intelligence over the entire northern section of the Soviet Union . On 4 July 1956 , the first U - 2 flight over the Soviet Union took place . Soviet leader Nikita Khrushchev angrily protested this overflight and feared that “ when they understand that we are defenseless against an aerial attack , it will push the Americans to begin the war earlier . ” This prompted the Soviet Union to develop new air defense systems . Strategic overflight reconnaissance in peacetime became routine U . S . policy . Project OXCART advanced aerial overflight reconnaissance capabilities with the development of the Lockheed SR - 71 Blackbird . Discontinuance . US reconnaissance overflights were discontinued after satellite reconnaissance was implemented in 1960 . After the 1960 U - 2 incident , Eisenhower had to confirm that overflights took place , and claimed that they were necessary for US security . However , Project Dark Gene , a CIA - Iranian program of intrusions into Soviet airspace to explore Soviet air defence systems , continued up to 1979 . More than 40 US aircraft were downed by Soviet forces and about 200 US servicemen were killed ; their families were given misinformation by the US military about how they died .