During WW2 the sinking of the Norwegian ferry HYDRO in 1944 was a pivotal covert operation. Allegedly carrying heavy water for the Nazi’s atomic bomb project, its true cargo remained a mystery. Promare, NOVA/PBS and Sperre AS collaborated to explore Lake Tinn’s depths dicovering the well preserved ship and evidence of the mysterious cargo. Analysis confirmed it was heavy water, shedding light on the Allies’ efforts to thwart the Nazi nuclear program. Despite attempts to sabotage German heavy water production, including a famous raid on Vemork, the ultimate destruction of the Hydro ensured the prevention of Nazi nuclear ambitions.