Hitler's plot to completely destroy London with an atomic bomb was very nearly a success, a new documentary has revealed.
Scientists and naval historians in Norway have found the boat which Nazis were using to transport heavy water - an ingredient for nuclear reactors.
Winston Churchill ordered the sinking of the 170ft SF Hyrdo ferry in 1944 - without knowing what the ship's secret mission was.
It was a choice which is now believed to have saved England's capital city.
Evidence of this has been dragged up 460ft from the bottom of a Norwegian lake around 100 miles from Oslo.
National Geographic teams working on the Drain the Oceans series found 40 barrels of heavy water when they virtually lifted the vessel - more than enough to push Germany a huge way to becoming a nuclear power.
About a ton of heavy water was discovered on the lake’s bed – proof that, without the heroism of a few soldiers, the Fuhrer could have dropped an atom bomb on London and, in the words of one scientist, ‘turned the war in the blink of an eye’.
Lake Tinn Norway where National Geographic teams have centered their investigations into Nazi transportation of heavy water
Winston Churchill ordered the bombing of SF Hyrdo ferry in 1944 as it carted heavy water to Germany
Heavy water has a unique atomic structure and is coveted for the production of nuclear power and weapons.
Naval historian professor Eric Grove told the Daily Telegraph: 'After the war, those involved in the German nuclear programme said that the loss of the heavy water was absolutely decisive. It stopped their reactor programme in its tracks.'
Norwegians began producing heavy water by 1934, above Lake Tinn at Vemork, making the country a target during the war.
In 1939 the nation began its 'uranium club'. Otto Hahn and Fritz Strassmann had put Germany ahead of its competition in the nuclear race after discovering fission - the radioactive decay process in which the nucleus of an atom splits into smaller parts.
However, the scientists needed heavy water because of its ability to control the fission process.
Nazis invaded Norway in 1940 and headed straight for the plant in Vemork.
Operation Gunnerside in 1943 was launched as London feared Hitler would use heavy water against his enemies.
Kirk Douglas starred in The Heroes of Telemark which was about the Nazis in Norway and the mission to blow up the heavy water plant
kirk Douglas pictured on set in 1965. Heavy water has now been found at the bottom of Lake Tinn in 40 barrels
Norwegian commandos blew up the plant entirely while the Hydro was sunk. However, they did not destroy all the German supply of heavy water which the Nazis began to move the following year by train and ferry.
But Churchill was one step ahead.
London had already given the order for Norwegian forces to attach a bomb to the vessel.
Years later the mission was documented in The Heroes of Telemark.
Dr Frank Soreide of the Norwegian University of Science and Technology told the Daily Telegraph: 'We wanted to go down and take up a barrel and prove that this was being shipped to Germany.'
Drain the Ocean will air weekly from September 6 on National Geographic.