NEWSLETTER NO. 360
We met the Periodic Table where elements are positioned according to their Atomic Number, chemically similar elements being adjacent. Naturally radioactive elements, like Radium, are continuously decaying as they spontaneously emit Alpha, Beta and Gama radiation from the nucleus.
If one bombards the nucleus of an element with neutrons or alpha particles, the nucleus will fission into two bits; this is termed Artificial Radioactivity and is accompanied by the release of an enormous amount of energy. The nucleus of the U-235 isotope can absorb a neutron and then fission, and also emit 3 neutrons to give a cascade or Chain Reaction. This needs a minimum mass of uranium-235, the Critical Mass (less than 10 kilograms). U-235 had to be separated from U-238 by physical means. The gaseous compound, uranium hexafluoride, was produced and this was diffused through thin sheets of nickel metal in an enormous plant at Oak Ridge (1.5 kilometres square).
By July 1945 enough metallic U-235 could be isolated to build one bomb. A block of U-235 was fired down a gun barrel into a second sub-critical block to give the critical mass and hence the chain reaction and atomic explosion. This was the bomb "Little Boy" which, on August 6, 1945, was dropped on Hiroshima from the B-29 Superfortress "Enola Gay". The explosion was equivalent to 15 000 tons of TNT.
U-238 behaves differently. Its nucleus absorbs a neutron, giving U-239. This, in turn, spits out two beta particles to yield a new man-made element of atomic number 94: Plutonium. This can be easily separated from uranium by straightforward chemical methods (solvent extraction into ether) and the Metallic Pu-239 isolated. This separation was done at Hanford, Washington. When bombarded by neutrons, the Pu-239 will fission and this became the basis for the second type of atomic bomb. To get a critical mass of Pu-239, several wedges of the metal had to be driven together by hollow-charge high explosive. This technique was tested at Alamogordo near Los Alamos on 16 July 1945 and it formed the bomb "Fat Man" that, on 9 August, was dropped on Nagasaki from the B-29 "Bocks Car". The explosive power was equivalent to 20 000 tons of TNT.
We saw pictures of the important personalities of Los Alamos; Dr Robert Oppenheimer and General Leslie Groves standing at ground zero at the Alamogordo test site; and also Captain William Parsons, the Navy explosives expert who fused the "Little Boy" while in flight to Hiroshima; and one of the expanding fireball - a sphere 100 metres in diameter after one-hundredth of a second.
Bill Brady, our vice-chairman, gave the main talk of the evening: The End of World War II in the Pacific, August 1945, thus marking the 60th anniversary of the dropping of the atom bombs on Hiroshima and Nagasaki. The Japanese military leadership ignored President Truman's Potsdam Proclamation, calling for unconditional surrender, in spite of being effectively defeated and on the verge of collapse. On 6 August 1945, therefore, in a last attempt to end the war, the American Superfortress B-29 bomber, "Enola Gay", piloted by Col. Paul Tibbettes, took off from the Marianas and delivered the atom bomb "Little Boy" on Hiroshima. Three days later another atom bomb was dropped on Nagasaki. Both bombs caused immeasurable loss of life and material damage.
The Japanese Emperor could not at first prevail over the military leaders to end the war, although after the actions at Iwojima and Okinawa, the Japanese were reduced to relying on the fanatical Kamikaze suicide raids. However, after the dropping of the atom bomb, the Emperor at last accepted the futility of prolonging the conflict and he supported the peace faction, accepting the Allied peace terms and ordering his forces to lay down their arms.
Bill then considered the events that led to the outbreak of war between America and Japan and the tragic events of Hiroshima and Nagasaki.
In December 1941 a superbly trained Japanese task force crossed 5 000 kms of the Pacific Ocean. Just off Pearl Harbour on 7 December, over 350 war planes took off from six Japanese aircraft carriers to launch the attack on the American Pacific battle fleet. This was followed by three months of hostilities during which the Japanese conquered an area the size of the North American continent. Reaching within striking distance of India and Australia, the Japanese launched operations simultaneously against British, Dutch and American possessions, thus delivering fatal blows to European imperialism.
The Japanese demonstrated that air power could be used effectively against shipping, when the battleship HMS Prince of Wales and the battlecruiser HMS Repulse were sunk off Singapore in attacks from the air. Eventually, every single Allied battleship in the Far East, ten in all at this time, was sunk or put out of action.
The American economic sanctions against Japan, including an oil embargo, crippled the Japanese economy. The Japanese had either to abandon their objective of Far East domination, or go to war with America and the Western Allies, in order to gain the mineral-rich Asian territories. Admiral Yamamoto, the commander of the Japanese Combined Fleet, proposed a sudden and paralysing knockout attack on the US Fleet at Pearl Harbour.
The Japanese underestimated the strategic problems associated with war with the USA and the anger that would be provoked by the attack on Pearl Harbour, and they overestimated their own capabilities in pursuing their proposed war against the US. The Pearl Harbour attack served to unite the Americans and mobilise all their economic and industrial resources.
With the American aircraft carriers in the Pacific (the Lexington, the Enterprise and the Saratoga) escaping damage, the US adopted carrier warfare, which in the long run was to give her victory after the Midway action when four Japanese aircraft carriers were sunk. The Pearl Harbour attack had proved to be a short-term tactical masterpiece, but a long-term strategic blunder. By November 1943 the balance of power had shifted to the US, as Japan had neither the manpower nor the industrial resources to ensure victory.
A titantic naval and air struggle ensued in the Pacific with the Japanese airpower smashed and the Japanese fleet annihilated at Leyte Gulf in October 1944. The Japanese then relied heavily on banzai charges and kamikaze attacks, both terrifying to the Americans, as suicide tactics became a vital part of the final Japanese defence.
After Germany's defeat in May 1945, the Allies were able to turn their full resources against Japan, with significant American gains from Guadalcanal to Okinawa in approaching the Japanese mainland, now braced for the final attack. This was the situation when the US decision was taken to drop the atom bombs, the morality of which has been hotly debated ever since.
The cessation of hostilities saw the remaking of Japan, beginning with the military occupation and the transformation of Japan into an ally of the West, due largely to the work of General Douglas Macarthur. Subsequently, nuclear energy has been harnessed to provide an efficient power source. Conflict has been avoided between the major powers since 1945, perhaps partly as a result of the horrifying prospect of the dropping of atom bombs again.
Dave Matthews, after thanking members of the Society for their concern during his recovery from serious surgery, thanked the two speakers for their fascinating talks.
South African Military History Society / email@example.com