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Hitler's Sunken Secret

Classroom Activity


Activity Summary
Students will use a viewing guide while watching a program about Nazi Germany's production of heavy water during World War II, and discuss answers to their questions after watching.

Learning Objectives
Students will be able to:

  • relate the history and significance of the Hydro's sinking.

  • note how recent documents have raised questions about the decision to sink the ferry.

Materials for each team
  • copy of the "Heavy Water Goes Down" student handout (PDF or HTML)

In 1940, the Germans captured Norway and took possession of the Norsk Hydro plant in Vemork. The Germans were interested in the plant because it could be used to manufacture heavy water. Although chemically like H2O, the hydrogen atoms in heavy water are made of the heavy isotope deuterium (heavy water is also known as deuterium oxide, D2O). The nuclei in each heavy water molecule contain a neutron in addition to the proton normally found in hydrogen. At Vemork, heavy water was produced through electrolysis, a process in which an electric current is conducted through an ion-containing solution.

Allied forces feared that the heavy water, which can help moderate a nuclear reaction, was a part of Germany's atomic weapons program. Norwegian Resistance workers at the Hydro factory provided the Allies with information about the plant. The Allies joined with members of the Norwegian Resistance to plan and execute three attacks on the plant prior to bombing the ferry believed to be transporting barrels of heavy water.

At the time of the Hydro's sinking, the sabotage was considered a success. However, some evidence suggests that the Germans may have planted barrels on the ferry that did not contain heavy water, and that the actual barrels with heavy water were shipped out of Norway to Germany at a later date.

  1. Organize students into five teams. Assign each team a set of four questions. The questions generally follow the sequence of the film. You can assign the questions in their current sequence, allocate them by themes, or choose a mix of simple and more complicated questions for each team.

  2. Distribute a copy of the student handout to each team before viewing. Discuss appropriate background information with students.

  3. Show the program and have students individually take notes on the questions their team has been assigned.

  4. After watching the program, have students meet in their teams to discuss their notes. Beginning with the first question assigned, ask teams to come to consensus on an answer. The team response should be written down as the answer to each question. Continue until all questions are answered.

  5. Have teams share the questions and answers that came out of their team work. (See Activity Answer for possible answers. Accept all reasonable answers.) Ask students in the rest of the class if they agree with what the team has presented. If students don't agree, ask them to explain why and provide evidence from the program that will support their opinions. When possible, expand upon a question or provide additional historical background for students.

  6. To conclude, discuss with students how the decisions were made to halt Germany's production of heavy water. What evidence was each decision based upon? How did time play a factor in the decisions? Do students think the Allied forces and Resistance fighters did or did not have enough information to base their decision on? Have students support the positions they choose.

  7. As an extension, have students generate questions they have about World War II. Group together students who have related questions. Have teams research and answer their own questions and present their findings to the class.

Activity Answer

Suggested answers to the questions listed on the student handout:

  1. Why were the Germans interested in heavy water? they wanted to build a nuclear bomb and heavy water is a key ingredient

  2. What was the name of the ferry used to transport passengers and (purportedly) heavy water? the Hydro How many people died when the ferry went down, and who were they? 14 civilians, and 4 German soldiers

  3. Why were historians interested in finding out what was on the Hydro? to discover whether heavy water was actually onboard the ferry

  4. Why was the Norsk Hydro plant built in the remote sRjukan Valley? the plant was situated near a large waterfall that could provide hydroelectric power

  5. What was originally made at the Vemork factory? fertilizer How was it made? hydrogen was extracted from water by electrolysis and then reacted with nitrogen in the air to make ammonia.

  6. What by-product was created at the plant? heavy water

  7. What did physicists come to realize about heavy water? that it could play an important role in the creation of a nuclear bomb

  8. How much water does it take to make 1 kilogram of heavy water? 50 tons

  9. Once the Allies understood how heavy water could be used, what action did they take? they teamed up with members of the Norwegian Resistance to try to destroy the Norsk plant.

  10. How did the Allies attempt to destroy the plant? What were the results of their efforts? the first attempt failed when weather prevented sending in 30 men by gliders; the second attempt was partially successful in bombing the heavy water production facility; and the third attempt succeeded in bombing the factory but not the heavy water plant.

  11. What did the Germans do to make even more heavy water? they used high-concentration cells and doubled the production apparatus

  12. What did the Allies and Resistance learn about the shipment of heavy water? barrels of heavy water were to be transported to Germany by train and then by ferry; rail cars would board a ferry named Hydro.

  13. What was the ethical dilemma related to sinking the Hydro? civilians would be at risk.

  14. Describe the operation that sank the Hydro. a team of saboteurs placed a bomb at the bottom of the ferry; 10 minutes after schedule, the ferry left the dock; 30 to 40 minutes later the bomb exploded and sank the boat

  15. Why was it important to locate the Hydro and examine the contents of the heavy water barrels? some historians did not believe the operation achieved its main objective, destroying German's supply of heavy water

  16. How would the investigators be able to tell if the barrel had lake water or heavy water in it? they would check the pH of the water—heavy water has a much higher pH (about 14.0) than lake water (about 9.0)

  17. Why did the investigators have to slowly maneuver the barrel as they lifted it from the water? the barrel could have exploded and released caustic potassium hydroxide-laden heavy water

  18. How did investigators know what percentage of heavy water the barrel was supposed to contain? the manifest showed that the barrel they were testing was 1.5 percent enriched

  19. What were the results of the testing? the pH of the barrel water was more than 14.0

  20. How did one of the saboteurs feel about the bombing when asked about it 60 years later? he said he didn't react to the bombing, but just swallowed what he had done; he noted he slept just as well at night as he had before the sabotage

Links and Books

Web Sites

NOVA—Hitler's Sunken Secret
Read a book excerpt about the Norsk Hydro plant bombing raid, learn how near the Nazis were to developing a nuclear weapon, examine spy messages regarding the Hydro ferry bombing, and discover how heavy water can be used to turn relatively common uranium into weapons-grade plutonium.

Physics 2000: Isotopes
Offers a tutorial on atoms and isotopes.

Sinking Hitler's Bomb
Retells the story of the sinking of the Hydro.


Assault in Norway: Sabotaging the Nazi Nuclear Bomb
by Thomas M. Gallagher. Harcourt Brace Jovanovich, 1975.
Recounts operations that destroyed a heavy water plant in Norway and a large shipment of heavy water on the way to Germany.

Heavy Water and the Wartime Race for Nuclear Energy
by Per F. Dahl. The Institute of Physics, 1999.
Reviews the scientific role that heavy water played in the wartime efforts and chronicles the air attacks on the Norwegian plant making heavy water.


The "Heavy Water Goes Down" activity aligns with the following National Science Education Standards (see

Grades 5-8
Science Standard F

Science in Personal and Social Perspectives
Science and technology in society

Grades 9-12
Science Standard F

Science in Personal and Social Perspectives
Science and technology in local, national, and global challenges

Classroom Activity Author

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Teacher's Guide
Hitler's Sunken Secret

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