He became an officer in the newly established Red Army and rapidly advanced in rank because of his great ability. During the Russian Civil War, he was given responsibility for defending Moscow. The Bolshevik Defence Commissar, Leon Trotsky, gave Tukhachevsky command of the 5th Army in 1919, and he led the campaign to capture Siberia from the anticommunist White forces of Aleksandr Kolchak. Tukhachevsky used concentrated attacks to exploit the enemy's open flanks and threaten them with envelopment. According to Tukhachevsky's close confidant Leonid Sabaneyev, in 1918, when he was in the service of the Military Department of the All-Russian Central Executive Committee, in his last overt display of neopaganism, Tukhachevsky drew up a project for destruction of Christianity and restoration of Slavic paganism. To this end, Tukhachevsky submitted a memo on declaring paganism as the state religion of the RSFSR, which although mocked, also received some serious discussion in the Small Council of People's Commissars, which commended Tukhachevsky for his "joke" and his commitment to atheism. Sabaneyev observed that Tukhachevsky seemed "as happy as a schoolboy who had just succeeded in a prank."