Vemork is the name of a hydroelectric power plant outside Rjukan in Tinn, Norway. The plant was built by Norsk Hydro and opened in 1911, its main purpose being to fix nitrogen for the production of fertilizer. Vemork was later the site of the first plant in the world to mass-produce heavy water developing from the hydrogen production then used for the Haber process. During World War II, Vemork was the target of Norwegian heavy water sabotage operations.