In March 1963, the Soviet Union flew two TU-16 Badger reconnaissance variants over southwest Alaska. The Badgers went unintercepted, as the sole fighter squadron in Alaska, the 317th, operated F-102 fighters, which had limited range and couldn't be refueled air-to-air.

The lapse in security led to a revised defense plan for Alaska that involved rotating squadrons of fighters visiting from the Lower 48, a system that would last until the end of the Cold War.

Although I cannot state categorically that the Soviets did not flyover the US, there were a number of factors that mitigated against a manned reconnaissance program on the scale of the USAF and CIA. One problem working against the Soviets was a technological gap. Although this narrowed over time, Soviet aerospace could not produce the aircraft with the performance (speed and range) equivalent to their US counterparts. For example, the MiG-25 became the basis for the main reconnaissance aircraft, and while its speed approached SR-71 levels, the MiG's range was quite terrible compared to the U-2 or SR-71. The Soviets never developed the tanker infrastructure to support the type of operations the US had. The Soviets at one point in the 1960s had an equivalent to the SR-71, the Tsybin RSR, but it the Tsyubin design bureau ran afoul of Tupelev and Mikoyan bureaus who wanted to use the resources demanded by the development of the RSR. This was a further hindrance to the development of a manned strategic reconnaissance program: the nature of Soviet military procurement. As it evolved in the 1930s and ossified in the Stalin Era, aerospace design bureaus had a powerful constituencies within the Soviet state. The state compounded this problem further by designating certain bureaus as their go-to for certain aircraft types (Tupelev= bombers, Sukhoi= ground attack, Mikoyan = fighters, etc.). This squashed innovation to a degree as something like a Soviet Skunkworks had to fight an uphill battle against an entrenched constituency. Finally, the Soviet, like the US, tended to shift towards satellite reconnaissance for overflights. This was partly because of the Soviet's intensive pursuit of SAM systems that rendered overflights very hazardous. Even the SR-71s did not risk direct overflights of the USSR, and while it could handle the SA-2s that downed Francis Gary Powers, the USAF brass was less confident that it could beat the 1970s generation of air defense.

Sources

Buttler, Tony, and E. Gordon. Soviet Secret Projects: Bombers Since 1945. Leicester: Midland, 2004.

Crickmore, Paul. Lockheed Blackbird: Beyond the Secret Missions. Oxford: Osprey, 2004.

Gordon, Yefim. MiG-25 'Foxbat', MiG-31 'Foxhound': Russia's Defensive Front Line. Leicester: Aerofax, 1997.

Palmer, Scott W. Dictatorship of the Air: Aviation Culture and the Fate of Modern Russia. Cambridge: Cambridge University Press, 2006.