Soon after the war Russia devoted a significant portion of its military spending to an ambitious shipbuilding program aimed at replacing lost warships with modern dreadnoughts. During World War I, the fleets played a limited role in the Eastern Front, due to heavy defensive and offensive mining on both sides. Characteristically, the Black Sea Fleet succeeded in mining the Bosporus, thus preventing the Ottoman Fleet from entering the Black Sea. After the revolution forced Russia to quit the war, the Baltic Fleet was evacuated from Helsinki and Tallinn to Kronshtadt during the Ice Cruise of the Baltic Fleet and many of the ships of the Black Sea Fleet found their last refuge in Bizerte.