The First War of Physics (32 page)

A uranium or plutonium bomb based on the gun method would be long and thin – about seventeen feet long with a diameter of about two feet. Serber named this design ‘Thin Man’, after the 1933 Dashiell Hammett detective story and the series of movies it had spawned. It was estimated that a plutonium implosion bomb, if implosion could be shown to work, would be a little over nine feet long and five feet in diameter. Serber named it ‘Fat Man’, for Kasper Gutman, the character played by Sidney Greenstreet in the movie
The Maltese Falcon.

Experiments to investigate how bombs with such dimensions might be dropped from a B-29 bomber began in August 1943. The plane, which was just beginning large-scale production for the American war effort, would need to be modified to carry the bombs to their target, and the experiments were designed to discover precisely what modifications would be required. To preserve security, in their phone conversations air force personnel would refer to these modifications as though they were being made to the planes in order to carry Roosevelt (Thin Man) and Churchill (Fat Man).

Slept most of the way

By August 1943 the situation in Denmark had changed. The terms of Danish government co-operation with the German occupying forces had included protection for Denmark’s 8,000 Jews. The growing boldness of the Danish resistance, and the increasing frequency of demonstrations, strikes and acts of sabotage, led German forces to declare martial law and re-occupy Copenhagen on 29 August. The Nazis started to arrest prominent Danish Jews.

On 28 September, Bohr received word from a sympathetic German woman working in the Gestapo offices in Copenhagen. She had seen the orders for Bohr’s arrest. A cable from Chadwick and Cherwell advised him
that his escape from Copenhagen had been granted priority by the British war cabinet. Bohr contacted members of the Danish resistance, and an escape route was prepared.

In early evening the next day, Bohr and his wife Margrethe walked to the Sydhavn quarter of Copenhagen close to the shores of the Øresund, the strait that separates Denmark from southern Sweden. They joined about a dozen others, including Niels’ brother Harald and Harald’s son Ole, in a small
Kolonihavehus
, not much more than a large garden shed, and waited for darkness to descend. At a pre-arranged time they crawled towards the beach, Bohr feeling rather self-conscious, and boarded a fishing boat that took them out across the Øresund. They then transferred to a large trawler and made their way to Linhamn, near Malmö in Sweden. They spent the rest of the night in the cells of the local police station in Malmö. Bohr travelled by train to Stockholm the next day, leaving Margrethe to await the arrival of their sons, who would shortly take the same escape route. Gyth was among those waiting at the station.

Gyth had alerted the SIS to Bohr’s dramatic escape, and was told to advise Bohr that he should come to Britain as soon as possible. There were believed to be many Gestapo agents in Stockholm and Bohr was one of the most widely known scientists in Scandinavia. To evade watchful eyes, Bohr was escorted by Gyth in a taxi to a building used by the Swedish intelligence services. They climbed to the roof, crossed to the roof of a neighbouring building, descended and took another taxi. Once safely installed at the home of Oskar Klein, one of Bohr’s colleagues from some years previously, Gyth passed on the message from the SIS and told Bohr that an unarmed Mosquito bomber was available at Stockholm’s Bromma airport to transport him to England.

But Bohr was concerned for the fate of the 8,000 Jews he had left behind in Denmark. On the evening of Bohr’s escape, two German freighters had arrived in Copenhagen harbour to transport the Jews to concentration camps in Germany. When he realised that the Swedish government had no plans to protest against the German intentions, Bohr made a personal plea to King Gustav V of Sweden.

In the meantime, a remarkable series of events had taken place. News of the impending deportation of Danish Jews had spread rapidly through the Jewish community. Within a few days virtually the entire Jewish population was hidden away, as offers of support flooded in from the general public. They hid in strangers’ apartments or cottages, in their homes, in churches and in hospitals, among the patients. In the midst of tragedy, the people of Denmark had risen to the aid of their fellow citizens. Fewer than 300 Jews were caught by the German sweep, which began on the evening of 1 October.

The Swedish protest was broadcast on radio on 2 October, signalling to Danish Jews that there was safe haven to be found in Sweden. A mass evacuation followed, supported by the Danish resistance, local fishermen, the Swedish coastguard and even a German naval commander who declared that his fleet of coastal patrol vessels was in need of repair and could not put out to sea. Over the following two months, 7,220 Danish Jews escaped to Sweden.

With the crisis averted, Bohr left for Britain on 5 October on board a twin-engine Mosquito bomber. There was room in the empty, unpressurised, bomb bay for only a single passenger. Bohr had talked incessantly prior to take-off and had paid little attention to the instructions the pilot had given him. As the plane climbed to 20,000 feet to avoid the risk of antiaircraft fire as it passed over the Norwegian coast, the pilot instructed Bohr to switch on his oxygen supply.

Unfortunately, the Nobel laureate’s head was too large for the helmet he had been given. As the message was relayed via headphones in the helmet, Bohr didn’t hear this instruction and promptly passed out through lack of oxygen. Sensing that something was wrong, the pilot descended steeply over the North Sea. By the time the plane landed, Bohr had recovered consciousness and appeared fine. He explained that he had slept most of the way.

Bohr was flown to Croydon airport near London, where he was met by Chadwick and an officer of the SIS. He was subsequently installed at the Savoy Hotel, where Chadwick informed him of the Frisch-Peierls memorandum, the MAUD report, Tube Alloys and the American bomb
programme. Bohr was completely astounded. He may also at this time have been able to set the record straight regarding Lise Meitner’s telegram. The reference to
MAUD RAY KENT,
to which Cockcroft had given such an ominous interpretation and which had led the MAUD Committee to be so named, was not a coded message at all. Maud Ray was a former governess to the Bohr children, now living in Kent.

Bohr dined with Anderson that evening. Anderson, who had been appointed Chancellor of the Exchequer in September following the unexpected death in office of Sir Kingsley Wood, explained that he would welcome Bohr as a member of Tube Alloys, part of a mission that was to be sent to join the American programme.

The impasse on Anglo-American co-operation on the atomic bomb had been resolved. A series of meetings through the summer months had helped to clear up misunderstandings about British post-war intentions. Britain’s desire was for an independent atomic deterrent against an anticipated Soviet atomic arsenal of the future. It was not Britain’s intention to acquire know-how at the American taxpayer’s expense for commercial exploitation after the war. This appeared to do the trick: Stimson and Bush were mollified. At Churchill’s request, Anderson had then drafted an agreement governing collaboration which Churchill subsequently amended.

In the meantime, Roosevelt himself had come to a decision, on the advice of Hopkins. He had decided that it was incumbent on him to honour the commitments regarding co-operation he had made to Churchill over a year before. Anderson and Bush talked Conant round. So, when Churchill tabled the draft agreement at the Quebec summit conference on 19 August, it was quickly (and, from the Americans’ perspective, rather too hastily) signed. The first four articles were virtually those of the AndersonChurchill draft. A fifth article set out the structure of a Washington-based Combined Policy Committee with representation from America, Britain and Canada. In the agreement Britain and America committed never to use the bomb against each other, never to use it against a third party without each other’s consent, and never to communicate any information about atomic weapons to third parties without mutual consent. This
agreement would cause considerable trouble later, but for now it meant the resumption of full collaboration.

The Americans accepted that the Manhattan Project should become the main focus of Anglo-American efforts to develop the atomic bomb, and that this should be supported by a British scientific delegation, or ‘mission’. Anderson wanted Bohr to join the 30-strong British contingent that was now due to travel to America.

Bohr’s son Aage, himself a promising young physicist, joined him in London a week later, and took the role of his father’s personal assistant. The rest of the Bohr family stayed in Sweden.

Raid on Vemork (2)

Tronstad was greatly concerned by the news that the Germans had managed to get the Vemork heavy water plant working unexpectedly quickly after the successful SOE raid in February. Skinnarland, reporting from a makeshift radio station on the Hardanger Plateau, had estimated that the plant would achieve full production in mid-August. Tronstad was also concerned that a new ‘combustion’ method of separation could, if adopted at Vemork, lead to production at a much accelerated rate. The job that the SOE had set out to do with operations Freshman and Gunnerside was clearly not yet completed. Production was again delayed by small, limited acts of sabotage, in which vegetable oil was added to the distillation vats. But it was again obvious that this could not continue indefinitely. The Vemork plant had to be taken out of commission.

Tronstad tried to devise further large-scale sabotage operations, but the defences at the plant had been greatly strengthened. Vemork was now surrounded by barbed wire fences and minefields, and the garrisons at Vemork and Rjukan had been substantially increased. A further commando raid seemed out the question. The only alternative appeared to be a bombing raid. Tronstad and Wilson remained firmly opposed.

But Groves was insistent. He did not trust the British. He had not been informed of the failed Freshman raid until after it had ended in disaster. He had learned of the Gunnerside raid through a casual remark made
by Akers in January. In the new spirit of Anglo-American collaboration embodied in the Quebec agreement, he now urged the British representatives of the Combined Policy Committee to agree appropriate action.

In fact, an SOE memorandum of 20 August 1943 had acknowledged that a bombing raid was the only viable option and should be given active consideration. The memo also advised that the Norwegian High Command and Norwegian government-in-exile should not be informed of such plans. By mid-October, a full-scale ground assault or a further sabotage raid had been firmly ruled out.

Groves was not prepared to take the risk that the German programme might be successful in producing, if not a bomb, then perhaps some sort of radiation weapon. Bohr’s recollection of his discussion with Heisenberg in September 1941, and the diagram of a bomb that Bohr believed Heisenberg had drawn for him, merely compounded the situation. Groves ordered a bombing raid, his first combat decision after a lifetime in uniform.

A force of about 300 B-17 Flying Fortresses and B-24 Liberators of the American Eighth Air Force took off from airfields in East Anglia just before dawn on 16 November 1943, in poor weather conditions. Part of this force headed for targets near Stavanger and Oslo to divert German fighters away from the main force heading for Vemork. The raid had been carefully timed to coincide with the lunch break, between 11:30am and noon, when most of the plant’s workforce would be off-site.

No fighters were encountered and the bombers arrived at the Norwegian coastline twenty minutes too early. The commander, Major John M. Bennett, ordered the fleet to circle back out over the sea and return for the bombing run at the right time. The decision traded civilian casualties for military: as the bombers returned to the coastline, one was shot down by anti-aircraft fire from the now fully alert coastal defences. The crew of a second parachuted into the sea as their plane spun out of the air with an engine on fire.

From their vantage point on the Hardanger Plateau, Haukelid and Skinnarland both watched as: ‘Scores of American bombers were flying across Norway in broad daylight as if no German anti-aircraft defences
existed. They began to circle over us and then proceed in an easterly direction, towards Rjukan.’

In the first wave of the attack about 145 bombers dropped more than 700 1,000-pound high-explosive bombs on the Vemork plant. Fifteen minutes later a second wave of about 40 bombers dropped 295 500-pound bombs on Rjukan. But in the Second World War so-called precision bombing was far from precise. The bombs fell everywhere. The plant itself received just two hits, damaging the top floors but leaving the electrolysis cells, in the basement, completely unharmed. The plant’s power station was hit, as was the nitrate plant in Rjukan. Twenty-two civilians were killed.

The Norwegians were absolutely furious, and lodged formal protests with both the British and American governments. They argued that the attack ‘seems out of all proportion to the objective sought’. Tronstad pointed out that he had given all the reasons why a bombing raid would not be successful four months before.

And yet the raid was successful, if not quite in the manner intended. The Germans had finally got the message that the Vemork plant was not safe, that the Allies would continue to attack it until it was utterly destroyed. Production of heavy water at Vemork was stopped and plans were laid to build a plant in Germany.

Oath of allegiance

Frisch was asked by Chadwick in November 1943 if he would like to work in America. ‘I would like that very much’, was his reply. ‘But then you would have to become a British citizen’, Chadwick warned. ‘I would like that even more.’ Within a few bewildering days he had pledged his oath of allegiance to the British Crown.

Chadwick had been eager to recruit the best scientists in Britain to join the delegation to America. To give the mission the best possible chance of success, he also sought to recruit nuclear physicists from outside Tube Alloys. Chadwick was well aware of Lise Meitner’s discomfort in Stockholm, and asked if she was willing to join her nephew in America. Meitner was unambiguous: ‘I will have nothing to do with a bomb’, she replied.