Forelle was a single-hull boat designed with internal ballast and compensating tanks.[1] She had fixed angled aft planes, and movable forward units for dive control. This boat had to be carried into action on board a surface ship and launched close to its target, as she was not fitted with a separate surface propulsion system.[1] She was equipped with two Whitehead torpedoes.
The Imperial Russian Navy purchased the submarine in May 1904 for service in the Russo-Japanese War.[1] It was shipped from Kiel to Liepāja by railway, together with a team of German engineers to train the Russian crew, and was commissioned at Kronstadt on 21 August 1904. It was then sent via the Trans-Siberian Railway to Vladivostok, arriving on 29 September, and joined the Siberian Flotilla on 2 October, becoming the first Russian submarine in the Pacific. Although the submarine did not see combat during the Russo-Japanese War, its presence had an important psychological effect.
Forel continued to operate out of Vladivostok after the war; however, by 1908 it was considered obsolete and was re-classed as a training vessel. The submarine sank in an accident on 17 May 1910.[1] The crew managed to escape, and the ship was salvaged from a depth of 26m (85feet). Vice Admiral Ivan Grigorovich authorized it to be returned to Liepāja for repairs, but shipping was never implemented.