In the early 1940s, both Germany and the United States had secret projects working on an atomic weapon. The basic ideas were known to physicists, but the design specifics and industrial scale production of fissionable material had to be worked out. By late 1942, the Manhattan Project was established by the U.S. and Britain to develop, test and employ the new weapon. The Allied leadership had one major fear: what if Hitler's world-class German scientists built an A-bomb first? The German work had to be stopped, at any cost.
Burning buildings during the 16 November 1943 raid on Norsk-Hydro Vemork plant at Rjukan. Courtesy of Norsk Hydro ASA.
Status of the German Atomic Program Early in WW II
In September 1941, Niels Bohr (Danish) received a visit from his friend Werner Heisenberg (German), both Nobel prize winning physicists prominent in the development of quantum theory. After the war, Bohr wrote that Heisenberg left "the firm impression that, under [his] leadership, everything was being done in Germany to develop atomic weapons." Bohr said that Heisenberg "gave no hint about efforts on the part of German scientists to prevent such a development." As soon as possible after the meeting, Niels Bohr passed this news to the underground in Denmark who relayed it to British intelligence.
To produce an atomic bomb, either enriched uranium or plutonium is required for the explosion. The Germans hoped to avoid the immense manufacturing investment needed to enrich uranium and instead wanted to build a relatively simple nuclear reactor that would produce plutonium. Such a reactor can be moderated -- to prevent a runaway reaction -- with either graphite or so-called "heavy water" (where deuterium replaces hydrogen). Flawed experiments incorrectly convinced the German scientists that graphite would not work, so they sought a source of heavy water for their plutonium production reactor.
The German Heavy Water Program in Norway
Norsk-Hydro Vemork plant at Rjukan. Courtesy of Norsk Hydro ASA.
The only industrial-scale production facility in Europe capable of producing heavy water for the German atomic effort was the Norsk-Hydro power station at Vemork, to the west of Rjukan in Telemark (region or state), a remote mountainous area deep in a long Southern Norway valley at the foot of Telemark's tallest mountain. There, large amounts of water and electricity were available for the heavy water electrolysis process, already in use for producing ammonia for nitrogen fertilizer. The power station was built of reinforced concrete, snug against the cliffside, with its critical processing machinery located in the basement. Its location and fortress-like nature made it almost impregnable from both ground and air attack.
From the start of the Nazi occupation of Norway in May 1940, the Germans made clear their interest in heavy water. They replaced the process equipment at Vemork with German-designed improved methodology and increased the production.
A Norwegian chemist who helped build the heavy water plant, Professor Lief Tronstad, had escaped Nazi rule and was living in England. He had become the secret service chief for the Norwegian government-in-exile. Working with British Intelligence, Tronstad confirmed basic information about the plant and remained convinced that the Germans, if not stopped, could obtain their objective.
Einar Skinnerland, a native of Vermok who also escaped Nazi-occupied Norway to become an agent in the Norwegian underground, agreed to undertake a mission to learn what was going on at the plant in his home town. At the end of March 1942, Skinnerland parachuted into a barren area near the plant and made contact with the plantís chief engineer who confirmed that there had been a great deal of German activity at the plant and that the production of heavy water was being increased. British intelligence recommended destruction of Norsk-Hydro Vemork at the earliest possible date, an objective that was quickly approved at the highest levels.
Assault on Vemork
The obvious course would be to destroy Vemork by bombing but that was actually quite hard to do. After study, it was determined that existing British bombers would be unable to hit the target precisely nor likely to destroy the concrete structure. Nearby ammonia tanks would likely explode in any attack causing large losses of civilian life. For the time being, aerial bombing was ruled out.
The destruction of the Vemork heavy water facility eventually involved a series of separate actions over a period of more than two years. The first of these was a commando insertion codenamed Grouse. On 18 October 1942, four Norwegians, recruited and trained by British Special Operations Executive (SOE), were parachuted into Norway, on the Hardanger Plateau (or Hardangervidda), for a reconnaissance mission to confirm details of the Vemork plant. They then provided ground support for the arrival of Operation Freshman, the planned follow-up assault.
For Operation Freshman, two RAF Halifax bombers towed Horsa gliders, each carrying an officer, 14 other soldiers, and two pilots. The teams were Royal Engineers of the First Airborne Division, specially trained to sabotage Vemork. The Grouse team set up a landing site at a frozen lake near Vemork, with a plan to lead the force from there to the Norsk-Hydro plant. Freshman was to destroy existing stocks of heavy water and as much of the production facility as possible. Following the attack, the force would disperse and head for the Swedish border, a doubtful proposition in wintertime.
Operation Freshman began on time on 19 November 1942, but ended in disaster. In bad weather and at the limit of their range, both Halifax tow planes missed their targets and lost their gliders. The gliders crash landed, killing many of the Royal Engineers instantly. One of the bombers hit a mountain, with the loss of all aboard. Glider survivors were rounded up by the Germans within a day. Although dressed in British combat uniforms, the men were tortured and interrogated cruelly, then executed. The Grouse team was left isolated on the Hardanger Plateau where they barely survived arduous winter conditions.
While the Grouse team hid in the Norwegian wilderness, both the Germans and the British made further plans:
The Germans, alerted to the British interest in targetting Vemork, improved the defenses of the site, and
The British, though shocked by the Operation Freshman disaster, still saw the potential of the Grouse team on the ground and went on to mount another operation.
On 16 February 1943, Operation Gunnerside delivered by parachute an additional six Norwegian commandos, along with weapons and supplies, dropped from a Halifax bomber. After a few days of searching, the Gunnerside team linked up with the hidden Grouse team. The joint assault force, using cover as students on a skiing vacation, reconnoitered Vemork from a safe distance and determined their best point of entry. On the night of 27-28 February 1943, the commando team climbed the cliffs of the gorge, slipped into the Norsk-Hydro plant, set explosives that destroyed the heavy water inventory (about five months production) and production machinery, and quickly faded away into the surrounding mountains, skiing toward the border with Sweden. Only one of the team was intercepted and he too, after harrowing adventures, made it to Sweden.
The Gunnerside raid was a great success, an almost perfect commando operation that achieved its objectives with no friendly casualties. The action was cited by British SOE as "the most successful act of sabotage in all of World War II." Immense personal courage was displayed and many medals awarded to participants. Gunnerside disrupted production at Norsk-Hydro, but British intelligence received notice of a resumption of German production at the site after only two months. The American Manhattan Project determined to put Vemork out of business permanently.
Eliminating the German Atomic Program
By mid-1943 the U.S. Eighth Air Force had perfected daylight bombing from bases in the UK, while increased security at Vemork precluded another commando raid. Therefore, a large bomber attack was planned. On 16 November 1943, as part of an even larger bombing mission over Norway, the Vemork plant and Rjukan were targeted by 143 B-17 Bombers. At 11:45AM they appeared over Vemork at an altitude of 12.000 feet. Seventy tons of bombs were dropped, but only 18 bombs hit the Vemork plant. The other bombs were spread over a large area, found more than 20 miles from the target area. Six civilian houses were destroyed and several damaged. One bomb hit a bomb shelter, killing all of its occupants, mostly women and children. A total of 22 civilians were killed in the attack.
The Norsk-Hydro buildings were wrecked, but the actual heavy water facilities, deep inside the plant walls and at the lowest levels, were only lightly damaged. As far as direct destruction, the November 1943 bomber raid had far less impact than Gunnerside. However, the bombers persuaded the German authorities that the Norsk-Hydro location was no longer secure for heavy water production; they decided to move everything to a laboratory in Germany.
Inventory at Vemork amounted to 1,350 pounds of heavy water and 14 tons of other fluid, to be shipped to Germany in 29 large drums. These were shipped by rail from Rjukan to Lake Tinnsjo where the train cars were placed on-board a train ferry, named the Hydro, on the way to the open sea and Germany.
British intelligence learned of the shipment and worked with local Norwegian resistance to get details of timing, at great personal risk. Three agents, Norwegian Knut Haukelid and two others from the Norwegian underground, travelled the lake on the same ferry, but 48 hours before the heavy water shipment arrived. At that time, the ferry was unsecured. They placed bombs on the ferry, with a timer that would explode when the Hydro, with the heavy water shipment, reached the center of the 1,300 foot-deep lake. At 10:00AM in the morning on 20 February 1944, the time bombs blew up the Hydro as planned. The German atomic program went to the bottom of the lake, along with 14 Norwegian civilians and 4 German soldiers.
After losing the Hydro with its precious cargo of heavy water, German atomic weapons development was doomed to fail. However, due to Allied uncertainly about the German's status, bombers continued to pound and destroy a number of German research laboratories until the end of the war, making doubly sure no atomic super-weapon would suddenly appear on the European battlefield before Nazi Germany was crushed.
Recommended Books about the German Atomic Energy Program
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