I’m old enough to remember when there were organizations that smuggled Bibles into the Soviet Union.
The Communist Party was officially atheist. As it was the only political party allowed, that meant the government was officially atheist. All but a tiny number of churches were closed and a number were dynamited. The Moscow Stretenskiy Monastery, for example, once had four churches. Now it has only one. Three of them were dynamited and the fourth was used as a barracks for the Soviet secret police.