The Allies have to control Turkey at the beginning of the Russian turn for Russia to move ships through the Straits.
Also, according to the rule book: “If a canal or narrow strait is controlled by a power not on your side, but with which you are not yet at war, you must ask permission to use it, which may be denied.”
So in a very theoretical situation, Germany could capture Turkey before being at war with Russia, and allow Russian ships to pass through the Straights. But I don’t think that ever happens.
