 The ferries were camouflaged and by January 1941 lack of coal resulted in the steamships being fired by wood.One of the byproducts at Rjukan was the production of heavy water—a key component in nuclear weapons, and necessary as a moderator in German nuclear designs.The hydrogen plant at Vemork was the first mass producer of heavy water, and in 1939 the German company IG Farben, owning 25% of the shares in Norsk Hydro, asked for permission to import five liters of heavy water into Germany, later denied due to a lack of an export licence.