Tinnsjø railway ferry was a Norwegian railway ferry service on Lake Tinn that connected the Rjukan Line and Tinnoset Line. The 30-kilometer (19 mi) long ferry trip made it possible for Norsk Hydro to transport its fertilizer from the plant at Rjukan to the port in Skien. The ferry services were operated by the company's subsidiary Norsk Transport from 1909 to 1991, when the plant closed. One of the ferries was in 1944 the target of the Norwegian heavy water sabotage when it was sunk to 430 meters (1,411 ft) depth to prevent Nazi Germany from developing nuclear weapons.