in may 1919, grebennik was drafted into the red army and served with the 42nd rifle division. he caught typhus and after recovery in january 1920 became a clerk at the ekaterinoslav governorate recruiting office. grebennik joined the communist party of the soviet union in september. in october, he transferred to the cheka and served in the krasny kommunistychesky battalion of the cheka donetsk division's 1st regiment. with the regiment, grebennik fought against the white army commanded by pyotr nikolayevich wrangel.