SF Hydro was a Norwegian steam powered railway ferry that operated on Tinnsjø in Telemark. The ferry operated between Mæl and Tinnoset between 1914 and 1944, connection the two railways Rjukanbanen and Tinnosbanen. The railway was used to transport raw materials to and fertilizer from Norsk Hydro's factory at Rjukan to the port in Skien. She was the target of the Norwegian heavy water sabotage on February 20 1944 when the ferry was sunk to 430 metes deep in Tinnsjø to prevent Nazi Germany from developing nuclear weapons.
Hydro was the second ship delivered for the service; the initial ship SF Rjukanfos had been deliverd in 1909, but soon proved too small for the service. Hydro was ordered from Akers Mek. Verksted on July 19 1913 at a bid of NOK 268.000; in the end she cost NOK 334.293. She was launched on December 10 1914, but showed a coal usage that was too high, and was rebuilt and relaunched on June 5 1915.
In 1929 Hydro was supplemented with a third ship, SF Ammonia; all three operated the route until the sinking of Hydro.
The German occupation of Norway (1940–1945) during World War II made Rjukanbanen the area for a massive struggle in between the Norwegian resistance movement and the Third Reich. In February 1940, before the occupation, the entire Vestfjorddalen and the docks closed for foreigners. On May 4 1940 German troops reached Rjukan, a month after the invasion of Norway had started. 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 for the Germany designs as a moderator. The hydrogen plant at Vemork was the first mass producer of heavy water, and in 1939 IG Farben, who owned 25% of Norsk Hydro at the time, asked to import five liters of heavy water, but was denied due to lack of an export license. In 1939–40 production at Vemork was 20 kilograms, by 1942 production had increased to five kilograms per day.
The first attempt from the resistance was Operation Grouse in October 1942, but failed and caught by the Germans; as a consequence passenger transport after April 7 1942 from Ingolfsland Station to Rjukan was only permitted for soldiers, police and workers at the plant and schoolchildren. All filled ammonia wagons were stored indoors in a tunnel with heavy guarding. On November 16 1943 the United States Air Force bombed the hydrogen plant; the attack killed 21 civilians but failed to touch the heavy water plant, located seven stories of reinforced concrete down.
The Germans decided to cancel production of heavy water at Rjukan, and move the remains of the potassium hydroxide—from which the heavy water was distilled—was to be transported to Germany. The resistance movement was aware of this plan, and considered blowing up the train at various places, but instead chose to target the ferry Hydro.
To minimize the civilian losses, Kjell Nielsen at Norsk Hydro delayed the tapping of the potassium hydroxide one day to allow the shipment to be carried on a Sunday. On Saturday February 19 1944 the plant director Bjarne Nilssen informed the railway that a wagon with potassium hydroxide would be sent with train number three the following day with departure from Rjukan at 8:55 and correspond with the ferry from Mæl at 9:45; the shipment would arrive at Tinnoset at 11:35. NSB car Lf4 no. 32628 was loaded with 39 barrels, of which five barrels were to be unloaded at Notodden. The wagons were set up at Rjukan on the Saturday, but failed a weight check, and part of the load was reloaded onto wagon L-84. The wagons were stored overnight with a single guard.
During the night to Sunday two people, Jon Berg and Oskar Andersen where on guard on Hydro. The saboteurs Alf Larsen, Knut Lier-Hansen, Rolf Sørlie and Knut Haukelid parked a few kilometers from Mæl and broke into the ferry quay by cutting through a fence. They entered the ship, but where discovered by one of the two guards; Lier-Hansen indicated that he was a worker, and wanted to sleep on board, in the end convincing the guard. Sørlie and Haukelid went below deck to the keel where they spent two hours placeing of explosives; they were placed it in a circular formation long. The explosion would blow out about one to two square meters (ten to twenty square feet) of the hull. The saboteurs left the ship unseen; Larsen and Haukelid left for Sweden while Sørlie left for Hardangervidda.
The timing was set to cause the ship to sink at the deepest part of the lake, but still close to shore to allow any survivors a hope of rescue. The ferry was a little delayed, with calm weather and . On February 20 1944 Just before reaching the lighhouse at Urdalen the bomb exploded; the ship immediately set direction for land. The ship's crew failed to loosen all the lifeboats, and there was no instructions for using the lifebelts. By the time the crew left the bridge, the ship had tilted so much port that they could walk down the side. At 10:30 Hydro had submerged, and settled at depth. Farmers from across the lake were soon in their boats and came to the rescue.
Eighteen people were killed but twenty-nine survived. Eight German soldiers in addition to a crew of seven were on board, the rest were passengers. Some of the Norwegian rescuers felt that the Germans should not be saved, but this attitude did not prevail and four German soldiers were saved. All but one of the twelve passengers below deck did not survive. Eight days after the incident SF Rjukanfos went out to the place of the sinking for a memorial service.
In the early 1990s the wreck of Hydro was found by a mini-submarine. 600 kg of heavy water was also found on board, leaving no doubt that Hydro was indeed carrying the heavy water the day it was sunk. Two of the barrels have been salvaged, and one of them can be seen at Norsk Industriarbeidermuseum at Vemork, Rjukan.