https://www.osti.gov/opennet/manhattan- ... ionage.htm"Soviet spies penetrated the Manhattan Project at Los Alamos and several other locations, sending back to Russia critical information that helped speed the development of the Soviet bomb ... In the United States alone, hundreds of Americans provided secret information to the Soviet Union, and the quality of Soviet sources in Britain was even better ... Soviet espionage directed at the Manhattan Project probably hastened by at least 12-18 months the Soviet acquisition of an atomic bomb. When the Soviet Union conducted its first nuclear test on August 29, 1949 (left), the device they used was virtually identical in design to the one that had been tested at Trinity four years previously."
Less well known, but perhaps as crucial, the Soviets lucked into acquiring some B-29 bombers that emergency landed in Soviet territory in 1944. These advanced aircraft were uniquely capable of delivering an atomic payload. Stalin soon had them reverse-engineered. I don't have an estimate for how much this accelerated Soviet aircraft design, but a few years seems plausible.
https://www.telegraph.co.uk/news/worldn ... -B-29.html"Von Hardesty, a curator of the National Air and Space Museum in Washington, said that the capture of such a technologically advanced aircraft by the relatively primitive Soviet aviation industry could be compared to America getting its hands on an alien spacecraft. ... One Russian general called it dar Bozhii [a gift from God] when it arrived, and it completely changed the Soviets' standing in the post-war world. Stalin had no aircraft that could be used as a strategic bomber and nothing near it. He realized how vulnerable this made him, so he made copying these planes a top priority for his military. ... By 1946, Tupolev had produced the Tu-4, a fully working version of the B-29, plugging a gap in Stalin's arsenal. Mr Hardesty said: "The British and the Americans were flabbergasted when Stalin rolled this out at an air show in the West in 1947 and they hurried to find out how it had been produced."
Suppose this combination of espionage, defections, and lucky accidents had failed, and the USSR requires an extra 18 months to build their bomb and a suitable airframe. Instead of the American nuclear monopoly ending in late August, 1949, it lasts until February, 1951.
I'd love to hear speculation on what changes.
As food for thought, here are some real events that in happened in that period:
- NATO meets for the first time (Sept. '49)
- Chinese Communists proclaim the PRC and is recognized by the USSR; Republic of China "Taiwan" forms on Formosa (Sept./Oct. '49)
- Indonesia wins independence from the Netherlands (Nov. '49)
- India recognizes the PRC (Dec. '49)
- UK recognizes the PRC (Jan. '50)
- Sen. Joe McCarthy claims list of communists in the the US government (Feb. '50)
- Jordan annexes the West Bank (April '50)
- South Africa implements Apartheid ('50)
- North Korea invades South Korea, starting Korean war (June '50)
- First broadcast by Radio Free Europe (July '50)
- Western allies rearm West Germany (Sept. '50)
- China occupies Tibet and enters Korean War (Oct. '50)
- Viet Minh guerillas attack Hanoi in French Indochina (Jan. '51)