the Atom Bomb

Introduction

Perhaps no other aspect of World War II is as controversial as the decision to drop the atomic bomb on Japan. One thing that should be made clear is the international and open nature of scientific inquiry on atomic physics right up to the start of World War II. This is because no one was trying to make an atomic bomb, even though many scientists were aware of the tremendous energy trapped inside the atomic nucleus. Work was underway in numerous countries to better understand the atom and perhaps find ways to harness its energy.

In this desperate new war governments became aware of this potential source of immense power. Germany, Japan, Britain with America all had active programs during World War II to develop atomic weapons. As the theoretical underpinnings of atomic energy came into focus so did the staggering complexity of the industrial effort required to make an atomic bomb. This is where Germany and Japan were left behind as the United States spent $2 billion to design, test and manufacture the atom bomb under the Manhattan project.

The U.S. military was doing its best to defeat Japan even as work on the atomic bomb was coming to a successful conclusion. By the summer of 1945 fire-bombing raids by B-29 bombers were methodically incinerating Japanese cities while a naval blockade essentially isolated Japan from what was left of its empire. Operation Downfall, the invasion of the Japanese home islands was well into its preparation phase as hundreds of ships gathered at Okinawa.

From a political stand point it would have been unthinkable not to use the bomb. All the money and effort going into building a super powerful weapon that is left on the shelf as American troops die by the thousands trying to take Japan and end the war. This is where the debate begins and has never ended over the morality of using such a terrible weapon.

The Atomic bomb Attacks

The decision to drop the atomic bomb was not a group decision, in the end president Harry S. Truman made it. Among the president's senior military commanders most felt that a massive invasion of Japan would probably be necessary to end the war, although each service still wanted to claim ultimate victory for itself. The Navy proposed that its ongoing blockade of Japan would eventually force surrender. Likewise, the Army Air Force saw victory in continuing the fire bombing raids by B-29 bombers now numbering close to a 1,000 that were currently laying waste to huge areas of Japanese cities. Of course the Army felt strongly that only an invasion and occupation by troops would secure complete victory.

Truman in fact approved the invasion of Japan code-named DOWNFALL before he later decided to authorize the use of the atomic bomb against Japan. No one knew exactly how the Japanese leaders would respond to an atomic bomb blast on one or even several of their cities. Excellent code breaking by the Americans did reveal however the steps Japanese were taking and planning to take in defending their country. The likely number of casualties the armed forces of the United States would suffer invading Japan was given as 200,000 to a million men, depending on the source. But everyone realized including President Truman, who fought in the first World War, that the number of casualties was more of a guess than a fact. The atomic bomb was seen as a potentially war winning weapon and in that hope it was used but no one alive then truly comprehended its horrifying power.

Hiroshima

The atomic bomb dropped on the city of Hiroshima was code named Little Boy. The design is relatively simple using a gun type arrangement to explosively force a sub-critical mass of uranium-235 and three U235 target rings together at high velocity causing a chain reaction.

Well before dawn on the 6th of August three special reconnaissance F-13As took off to report the weather over the primary and secondary targets. Colonel Tibbets lifted the Enola Gay off the runway at 2:45 A.M. shortly followed by two other B-29 bombers.

Navy weapons expert Captain William Parsons armed the bomb in flight, as it had been deemed too risky to arm before take off in case of accident, possibly wiping out the entire base.

At 7:42 came the coded message from the Hiroshima weather scout recommending bombing the primary target. Enola Gay was now at 26,000 ft and in a slight climb at a little less than 200 miles an hour. For the first time, his crew was told that they were about to deliver an entirely new type of weapon of staggering destructive power.

At 8:05 Enola Gay was coming in at 30,800 ft, followed by the observer planes, and less than 50 miles from Hiroshima. Major Thomas Ferebee, the bombardier, took up position in the Plexiglas nose to fix the crosswire of his sight on the city's T-shaped Aioi Bridge.

Through the shimmering haze, Ferebee made out the bridge and locked the cross hairs of his bombsight. The final fifteen seconds to bomb drop were automatic. At seventeen seconds past 8:15, the bomb bay doors opened and "Little Boy" plummeted free.

At 1,800 ft, the barometric pressure device triggered the detonating mechanism. In a few milliseconds a brief flash had become an engulfing ball of light and destructive energy.

With this release of apocalyptic power 75,000 people were killed and 48,000 buildings destroyed. Strategic air power reached a terrifying new level of destruction in the smouldering ashes of Hiroshima.

Comparison of Atom Bomb Attacks with other Bombing Raids

Data from the US Strategic Bombing Survey, Japanese official counts, and U.S. government / military documents assessing the damage caused by these weapons.

Notes:
Many of the wounded in the atom bomb attacks would die in the coming days, months and even years due to radiation exposure and burns.

The terrain and spread-out nature of Nagasaki reduced destruction of life and property somewhat despite Fat Man's greater destructive power.

Nagasaki

The atomic bomb dropped on Nagasaki was code named Fat Man and used plutonium as the fissionable material. Plutonium is a man-made element that is more efficient than uranium as a fission source. The design is also more complicated than the Little Boy atomic device. It relies on a rapid and simultaneous implosion of a fissionable shell into a critical mass.

A B-29 bomber named "Bock's Car" took off on August 9, 1945 to drop another atomic bomb. This 10,000 lb weapon was known as "Fat Man" and promised by its design to be even more destructive than "Little Boy." Fat Man detonated 1,650 ft (500 m) over Nagasaki with the force of 21 thousand tons of TNT at 11:06 am.

The explosion over Nagasaki was more powerful but the terrain and layout of the city resulted in fewer deaths. Still, 40,000 were killed instantly and 45,000 more would die later from burns and radiation. The previous day Russia had declared war on Japan and launched a huge offensive involving thousands of tanks and self propelled guns.

Name: Little Boy
Type: Uranium gun-type fission
Weight: 9,700lb (4400 kg)
Length: 10 ft, 6 in (3.2m)
Diameter: 29 in (0.737m)
Explosive Yield: 15,000 tons of TNT

Name: Fat Man
Type: Plutonium fission
Weight: 10,000lb (4535 kg)
Length: 10 ft, 8 in (3.25 m)
Diameter: 5 ft (1.52 m)
Explosive Yield: 21,000 tons of TNT

Manhattan Project

Introduction

On 2 August 1939 some scientists wrote to President Roosevelt of efforts in Nazi Germany to purify Uranium-235 with which might in turn be used to build an atomic bomb. It was shortly thereafter that the United States Government began the serious undertaking known only then as the Manhattan Project. The Manhattan Project was designed to research and production that would produce a usable atomic bomb. The Project was named after the Manhattan Engineer District of the US Army Corps of Engineers, because a lot of the early research was done in New York.

In 1942 General Leslie Grove was chosen to oversee the project while the brilliant young physicist Robert Oppenheimer was appointed to lead the scientific team.

Initial Research

This came in the latter part of 1942 with work done at Chicago University led by Enrico Fermi. He developed and brought to life the world's first atomic reactor (atomic pile.) In affect this was a slow motion atomic bomb proving that the concept and scientific principles were sound. The atomic reactor undergoes nuclear fission (the same process that powers an atomic bomb) but, of course, under controlled conditions.

Testing

A remote site on the Alamogordo Bombing Range, code named Trinity was chosen to test the world's first atomic bomb. Stationed on top of a 100-foot tall steel tower was a plutonium implosion device ( Fat Man type atomic bomb ) It was detonated at 5:29:45am on July 16, 1945. The explosion vaporized the tower, left a 300 foot wide crater some 8-10 feet deep and released energy equivalent to 15,000 - 20,000 tons of TNT. The Trinity site is located about 120 miles (193 km) south of Albuquerque, New Mexico.