Knut Haukelid and Arne Kjelstrup basically starve through the winter and spring of 1943, dodging angry German patrols.
Unfortunately, as of summer of 1943, the Germans have already started rebuilding the equipment the guys had destroyed at Vemork—and by August, they're shipping heavy water to Germany again. Curses.
Desperate to stop the production process, the U.S. Air Force unleashes a torrent of seven hundred bombs over Vemork. It doesn't do enough damage to the plant to halt production, but it does convince the Germans that they need to move elsewhere. Mission partially accomplished.
In February of 1944, the Germans begin emptying their heavy water machines and prepare for a humungous shipment of all of their precious cargo to Germany.
Catching wind of this plan, General Groves taps Knut Haukelid to perform daring sabotage once more.
Haukelid and fellow Norwegian resistance-fighter Rolf Sörlie get the Germans' plans from an engineer working in Vemork. The heavy water is supposed to be transported in forty barrels by train, then ferryboat across Lake Tinn, and then by train again until they reach the coast, where they're to be shipped across the North Sea to Germany. All of this will occur under really heavy guard and air surveillance because the Germans know it's a valuable target.
Haukelid and Sörie recruit Knut Lier-Hansen, a local surveyor with nerves of steel.
After formulating—and scrapping—several plans, they decide they need to attack when the barrels are being transported via ferry over Lake Tinn. If they can sink the boat over the deepest part of the lake then bingo-bango, problem solved.
At 1:00AM on February 20, Lier-Hansen, Haukelid, and Sörlie sneak onto the ferry Hydro, which is slated to carry the barrels of heavy water later that morning.
On the boat they discover the ship's crew is below deck playing a rowdy game of poker.
A Norwegian night guard surprises the men, and they act like they're just trying to hide supplies from the Germans in case of a raid. He's sympathetic to their cause, so he directs them into the bilge (below the boat).
Haukelid and Sörlie climb down into the bilge to set up a bomb in the front of the boat, knowing that if they blow a hole there the boat will go down pretty darn fast. (Think: Titanic).
They rig the bomb with two alarm clocks that will go off, setting the bomb off in the process, at 10:45AM.
The water is loaded onto the boat at 10:15AM, along with fifty-three people (about half of them Norwegian civilians).
As planned, the bomb goes off at 10:45AM, sinking the ship and the heavy water along with it, within four minutes of the explosion.