During the opening months of the Russo-Japanese War, Kataoka was placed in command of the 3rd Fleet, a collection of antiquated ships nicknamed the "Funny Fleet". Despite the motley assortment of obsolete ships, Kataoka won distinction commanding the fifth and sixth battle divisions from the cruiser during the Battle of the Yellow Sea and later from the cruiser during the Battle of Tsushima. He also led the naval expedition to seize Sakhalin prior to the conclusion of the Treaty of Portsmouth.