In the Imperial Russian Navy, Soviet Navy, and Russian Federation Navy, the word "flotilla" has tended to be used for "brown-water" naval units – those operating not on the oceans and real seas, but on inland seas or rivers. Among the former are the present-day Caspian Flotilla, the early-20th-century Satakundskaya Flotilla, or the Aral Flotilla of the 1850s; among the latter, the Don Military Flotilla (which was created several times over more than 200 years), the Dnieper Flotilla (also extant in the 18th and 20th centuries), the Red Volga Flotilla, which participated in the Kazan Operation during the Russian Civil War, and the Danube Flotilla. In the 18th century, the term also applied to the comparatively small fleets operating on those seas where Russia did not have much naval presence yet, e.g. the Okhotsk Flotilla.