Norsk Hydro’s factory at Vemork, Rjukan, played a central role during the Second World War. The factory produced heavy water, which was important to the German nuclear research program. After a bombing of the factory, led by the allies on November 16th 1943, it was decided to move the production to Germany.
The saboteurs discovered that the Germans planned to ship all the semi-finished products from Vemork to research centres in Germany. Orders came by radio from London to destroy the cargo during transport. The weakest link was the journey by train ferry over the Tinnsjø lake.
The heavy water cargo was closely guarded at all times, but the boat that was to transport the shipment stood unwatched the night before. One of the three saboteurs had experimented with a timer and detonating mechanism, and he tried to set the explosion to go off when it would be easiest to rescue passengers.
An explosion in the bow sank the "Hydro" on 20 February 1944, and ended the last chapter in the story of heavy water in Norway. The sinking of the "Hydro" cost four Germans and 14 Norwegians their lives.
The ferry's departure was unfortunately delayed. However, far more lives would have been lost if the explosion had been set off on a weekday. There were never many passengers on Sundays.
Taken from www.hydro.com/en