From Great Globe Itself by William C. Bullitt, 1946

The Petrograd Soviet was composed of varying numbers of workmen and soldiers—rising occasionally to as many as 2,500, chosen from the factories and battalions in the city—plus the leaders of the various socialist parties. All non-socialist parties were excluded from the Soviet, and at the outset the largest representation in it was held by the Socialist Revolutionaries, who claimed to represent the peasants. The Social Democratic Party, which was strong among the factory workers, was split between Mensheviks, who believed that socialism should be achieved by democratic methods and could not be established successfully in Russia until the country had been more industrialized, and the Bolsheviks, who wanted to introduce socialism immediately by any methods whatsoever. It was only after the German General Staff, knowing that Lenin was its better enemy, but estimating correctly that Lenin would take Russia out of the war, had sent the Bolshevik leader back to Leningrad [i.e. Petrograd] in April 1917,⁹ that the Bolsheviks began to call themselves Communists. They adopted the name Communist Party on March 18, 1918.

    ⁹Wheeler-Bennet, Brest-Litovsk, the Forgotten Peace, p. 35.

pages 51-2.