Zaitsev served in the Soviet Navy as a clerk in Vladivostok. When Nazi Germany invaded the Soviet Union during Operation Barbarossa, Zaitsev, like many of his comrades, volunteered to be transferred to the front line. He was a chief petty officer in the Navy and was assigned the rank of senior warrant officer upon transfer to the army. He was assigned to the 1047th Rifle Regiment of the 284th "Tomsk" Rifle Division, which became part of the 62nd Army at Stalingrad on 17 September 1942.