Sam Eyde built the Vemork power plant in 1911. The power plant would supply energy to Norwegian Hydro's production of fertilizer, to prevent the world from famine.
Heavy water was a by product
Heavy water was a byproduct of the hydrogen gas that was produced at Vemork.
The chemical formula of heavy water is D2O. Heavy water looks like water, but is about 10 percent heavier. Plain water (H2O) has two hydrogen atoms and one oxygen atom. In heavy water there is deuterium instead of hydrogen, and while regular hydrogen has one proton in its nucleus, the deutrium has both one proton and one neutron. Thus, it becomes heavier.
What would the Germans with heavy water?
Research showed that heavy water can be utilized in nuclear reactors, beacuse heavy water can slow the neutrons so they can react with the uranium in the reactor.
The Allies feared that Germany would use heavy water from occupied Norway to develop nuclear weapons, and this was the reason for sabotage attacks against heavy water plant at Vemork.