When the United States stopped all publications related to nuclear developments, that alarmed Georgy Flyorov[0]: He took it as a sign that we were building a bomb. He wrote to Stalin, and that helped start the Soviet Atomic Bomb Project[1].

[0]: https://en.wikipedia.org/wiki/Georgy_Flyorov

[1]: https://en.wikipedia.org/wiki/Soviet_atomic_bomb_project