Adolf Hitler's plans to blow up London with a nuclear bomb very nearly succeeded, a new documentary has revealed.

A Nazi ship with the secret mission of transporting heavy water – an ingredient used for nuclear reactors – has been found by scientists and naval historians in Norway.

The 170ft Hydro ferry, which Winston Churchill ordered to be sank in 1944, has been dragged up from the bottom of a 460-feet Norwegian lake near Oslo.

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Churchill was unaware of the ship's purpose but ordered its sinking anyway, a choice that is now believed to have saved Britain's capital city.

The National Geographic series "Drain the Oceans" sees teams discover 40 barrels of heavy water when they virtually lifted the vessel.

This quantity of heavy water would have been more than enough to catapult Germany on her way to becoming a nuclear power.

Naval historian professor Eric Gove told the Daily Telegraph: "After the war, those involved in the German nuclear program said that the loss of heavy water was absolutely decisive. It stopped their reactor program in its tracks."

Norway became a target of the Allies after it began producing water in 1934, above Lake Tinn at Vemork.

Five years later, in 1939, the country began its "uranium club." Otto Hahn and Fritz Strassmann had placed Germany at the head of the pack in the nuclear race after they discovered fission.

Fission is the radioactive decay process where an atom's nucleus splits into smaller parts.

The scientists needed heavy water in order to control the fission process.

After Hitler invaded Norway in 1940, he ordered his troops to move straight for the nuclear plant in Vemork.

Consequently, Operation Gunnerside was launched in 1943 after Britain feared Hitler would use this substance against his enemies.

Despite blowing up the plant while the Hydro was sunk, the Norwegians did not destroy all the Germany supply of heavy water the Nazis began to move the following year by train and ferry.

However, Churchill was already a move ahead.

He and his generals had already ordered their Norway counterparts to attach a bomb to the vessel.

The mission was later documented in The Heroes of Telemark.

"Drain the Ocean" will appear on National Geographic every week since Sept. 6.

This story originally appeared in The Sun.