WWII: The Scientists' War

Exodus of the European Scientists

In the previous post, Fermi's flight from Fascist Italy to the United States in 1938 was briefly mentioned. In fact, this emigration was far from atypical; the United States was increasingly called home by a number of European Jewish scientists (or in Fermi's case, European scientists with Jewish family members or spouses).

Fermi's defection completed a powerful assemblage of theoretical nuclear physics talent in America. Some of the names are all-time legends in physics: Albert Einstein had come to the US in 1933, Edward Teller in 1935, and Leo Szilard earlier in 1938. Between Germany, Hungary, and Italy, the major Axis or Axis-aligned European powers had hemorrhaged some of their best brains for the sake of their insane national liberations.

Albert Einstein (1921)

Einstein seemed amazingly prescient about the future of Nazism. Einstein was vacationing in America in 1933 when Hitler came to power in Germany. Even though fascist governments were generally seen as benign by the world at large (Mussolini was praised for "getting the trains to run on time"), Einstein had lost faith in German democracy permanently, and he already knew of Hitler's stance on Jews. Einstein never returned to Germany, and he became a naturalized American citizen in 1940. Leo Szilard's letter to President Roosevelt in 1939 was the genesis of the atomic bomb project. Einstein did not draft the letter, but it is invariably called "the Einstein letter" because Einstein signed it himself. The professor must have succumbed to pressures from fellow scientists, who knew how revered he was all over the world, and insisted that only the magical name "Einstein" would be able to command the attention of the US president.

Einstein was largely a pacifist, and his participation in the Manhattan Project was nil, but his theories made the detonation of an atomic device possible. He later regretted his role in starting the program, but waffled on whether or not it was the right idea at the time, sometimes saying it was necessary to do so before the Germans did, and sometimes falling back on his pacifism. Einstein's last years were marked by political support for the newly-created state of Israel, founded in 1948.

Other prominent scientists rendered refugees included Otto Stern (German, emigrated 1933) Stanislaw Ulam (Polish, 1941), Ugo Fano (Italian, 1939), and Felix Bloch (Swiss, 1939).

Niels Bohr (1922)

The legendary Niels Bohr was a Danish Nobel laureate from 1922, and he initially resisted any affiliation with any government's nuclear program. Clearly the rope would tighten around him at some point; Denmark was occupied by the Nazis in 1940. Bohr was tipped off that the Germans planned to arrest him and force him to work on their nuclear bomb project in 1943, and the Danish Resistance herded Bohr and his family out of the country to neutral Sweden, which provided him with passage to Britain, from which he continued on to the United States.

Bohr was a minor advisor to the Manhattan Project, although he made note of the fact that he was among many distinguished peers and had fallen somewhat behind on the times: "This is why I went to America. They didn't need my help in making the atom bomb." Despite this, Bohr's work on atomic structure and quantum mechanics are essential contributions to modern physics.

It would be somewhat unkind to say that America was weak in physics prior to this WWII influx, but the public was largely unaware of the names of the people whose theories would be so critical just a few years later. More to the point, few of the greatest American folk heroes were scientific men. Thomas Edison was certainly a gifted, hardworking inventor, but his work was entirely empirical and he was uninterested in theory or mathematical proofs. Consequently, the work of Edison was always done with what was already understood and measurable physically, and could never be thought of as revolutionary or theoretical. Henry Ford likewise "went with the gut" when it came to knowing the right way to do it. 

Philo Farnsworth (1939)

I'd like to take this opportunity to nominate Philo Farnsworth as the most unsung American physics prodigy of all time. As a 14-year-old high school freshman in 1921, he conceived of how to transmit television signals electronically. He was persuaded by his high school teacher to keep pursuing the idea until eventually it became the world standard. The young man never received a college degree and only took a few classes at Brigham Young University in Utah before financial issues forced him to take care of his family. Farnsworth's idea eventually became the only standard for television broadcast and reception for the rest of the 20th century. Astonishingly, Farnsworth was virtually unknown for his pioneering theories, memorably stumping the panel on the TV show I've Got A Secret in 1957 regarding his secret: "I invented electronic television." Farnsworth went on to design a small device (Farnsworth-Hirsch Fusor) capable of generating nuclear fusion, but frustratingly, it was unable to produce power from this reaction. Farnsworth was never a household name and it never will be, but he was endlessly influential and held 165 patents, all without a college degree. I tend to think of Farnsworth as a sort of 20th century version of Michael Faraday, who was even weaker in terms of formal education, but had extraordinary intuition and a gift for effective experimentation. The difference is that Faraday's name is still widely known, but Farnsworth is as obscure now as he was 60 years ago.

Going back into the 19th century and earlier, the Americans always remained an inventive people, but they did not have the same hard science background as was flourishing in Europe, Germany in particular. From 1901 to 1933, Germans held 11 Nobel Prizes in Physics, more than any other nation, while the Americans held just 3. Over the 1930s and through WWII, American scientists gained 4 more, while Germany gained none. Since WWII, over 75 Nobel Prizes in Physics have been awarded to Americans, and the American people (either native- or foreign-born) increasingly became the dominant nationality in physics. As of 2012, this trend seems to show little slowdown.

Vannevar Bush during WWII

The Proximity Fuze

The most widely-known American-born physicist in the prewar era was probably Vannevar Bush, who did pioneering work in analog computing and later was a trusted confidante to FDR in terms of cooperation between government demands and the body of scientists. Bush's reputation is stellar in the 21st century, but he is sometimes remembered most for his pessimism regarding innovation, saying in 1944 that "I don't see how a serious scientist or engineer can play around with rockets." Bush's stewardship of the Allied effort to develop a proximity fuze ranks as one of the most difficult and complicated engineering challenges of the war, even compared to the Manhattan Project. The VT (variable time) fuze was the first-generation proximity fuze and it had the following things in common with the contemporaneous nuclear bomb:

1. The Germans had a concurrent development program that failed to invent the same thing, either because of lack of scientific knowledge or Hitler's insistence on six-month timetables for results, killing most of the more ambitious engineering goals.
2. However, the American project was late in coming, and the UK had independently started its project earlier. The success of the proximity fuze was most primarily due to the raw materials, quantity of engineering manpower, and funding that America had, which Great Britain did not. In the case of the nuclear bomb, the British program "Tube Alloys" predated the Manhattan Project, but it never came close to success during the war because it simply did not have the funding or the quantity of scientific genius behind it. Even though the American English word for this device would be "proximity fuse", the standard term is by consensus "proximity fuze", using the British variant, probably because the British first started the research.
3. The American effort was led by a native-born American under US military control, and the contracts were provided to American companies, notwithstanding the British influence which was subsumed into the American project, which was thereafter treated as a joint Allied project and shared fully between the UK and USA.
4. The success of the project was of extreme importance for the Allies. Bush estimated that proximity fuzes increased the effectiveness of anti-aircraft artillery sevenfold. For their effectiveness in land-based artillery, Patton claimed that the invention of the fuze "required a full revision of the tactics of land warfare," which seems almost great enough praise to be used to describe the atomic bomb.
5. Usage was limited because of the enormous fear that the Allies had that the technology would fall into enemy hands. Of course, the Americans took great care in delivering the first two atomic warheads. Although individual proximity fuze-equipped munitions were infinitely cheaper and more replaceable than nuclear weapons, the American War Department decided that these fuzes should only be used in places where they could not be captured (especially shooting down incoming V-1s over British soil). Eisenhower protested the stupidity of this decision, eventually getting proximity fuzes on the front line in time for the Battle of the Bulge in 1944-1945, resulting in terrifyingly successful bombardments of unprepared German positions. A similar request by MacArthur in 1950 to allow the use of nuclear weapons in the Korean theater was a complete failure, since Truman feared the Soviets would retaliate in kind. No US commander has ever seriously requested nuclear weapons in any war since the Korean War. It's possible that only MacArthur's legendary status made him arrogant enough to make such a suggestion to the US President, and that any US general who made such a suggestion in the subsequent political climate would have been relieved of duty hastily, with an immediate psychiatric evaluation afterwards.
6. The scale of the research and development amounted to hundreds of millions of dollars. The total spent by the US military on 22 million VT fuzes during WWII amounted to over $1 billion. Per-unit cost fell from $732 at the outset, to just $18. The Manhattan Project was only somewhat more than twice the price, and it produced a total of four nuclear weapons by the end of the war (one test, two dropped, one ready by the end of August 1945) making it a pretty good deal, at least to modern sensibilities.

Nuclear Weapon Types

Of course there were many other American WWII scientists of great importance: Nobel Prize winners Arthur Compton (discoverer of the Compton Effect) and Ernest Lawrence (inventor of the cyclotron) were two American physicists who offered a great deal to the Manhattan Project. Compton, like Fermi, was affiliated with the University of Chicago, which was where the earliest efforts at nuclear fission reactors were undertaken. Lawrence invented the calutron, a device for separating the isotopes of uranium. Scaled up to massive proportions at the Oak Ridge Site, Lawrence's calutrons used obscene quantities of electric power and had a dismal yield at first, but ultimately they produced enough uranium-235 for Little Boy, the bomb dropped on Hiroshima. This single bomb accounted for roughly half of the existing U-235 in the world. It was so much more expensive to build a gun-type uranium weapon that it was only done because it was basically guaranteed to work. The design was as simple and solid as conceptually possible, and a test was neither prepared for, nor carried out.

Plutonium as an alternative to uranium has become the standard of nuclear weapons. Plutonium gun-types were envisioned ("Thin Man") but they would never have worked due to the higher spontaneous fission of plutonium. Trinity and Fat Man were implosion-type plutonium weapons. These were more complicated, but once the concept was proven in the test, they were the obvious choice for mass production. Difficult though it was to produce plutonium in reactors, it paled in comparison to getting enough U-235 for a gun-type weapon.

The principle of operation of a gun-type weapon is to fire a sub-critical quantity of fissile material into another sub-critical quantity of fissile material. Together, when the materials are brought together, they form a critical mass, and a nuclear chain reaction occurs. The gun-type can be thought of as a stepping stone to more sophisticated nuclear weapons, although it was roughly as powerful as the earliest implosion-type weapons. The US developed this method not because it was cheaper or more effective, but because the scientists felt absolutely certain that it would work, and it was designed in such a simple manner that it was practically foolproof. Because it was designed to always work, the system is extremely dangerous for long-term storage, since many failure modes will result in an unintended nuclear explosion. Although this is much simpler, most early nuclear programs have not tried it because of lack of sufficient uranium, since so much is required. Only the US and South Africa have developed gun-type weapons. South Africa has completely given up on nuclear weapons since 1989, and there have been no gun-types in the US arsenal for decades.

The implosion-type weapon uses a single sub-critical mass of plutonium, achieving criticality by the simultaneous detonation of multiple explosive charges that compress it. Unlike with the gun-type, this is not foolproof, and it is relatively safe because a combination of failures that would cause an inadvertant detonation is virtually impossible. Making it happen in the first place is difficult, and so this was why the Manhattan Project scientists chose to test the device (Trinity) before dropping an identical device on Nagasaki (Fat Man). As production quality improved, implosion-type nuclear weapons developed to the point of utter reliability and multiple layers of safety. All other national nuclear weapons programs have only used the the implosion-type, including the UK, France, the Soviet Union (later Russia), the People's Republic of China, India, Pakistan, and North Korea.