Many people are aware that the "Fat Man" atomic bomb tested at Trinity Site on July 16, 1945 was fueled with plutonium and an identical one was Dropped on Nagasaki on Aug. 9. Most don´t realize that the Trinity test also proved the tools and procedures which were to be used in the Pacific in assembling and preparing the bomb for use on Japan. At the time of the Trinity test many of the bomb´s components were already on their way to the tiny island of Tinian where they would be assembled.
White Sands Missile Range has a MK III atomic bomb casing on loan from the Dept. of Energy which is displayed at the range´s museum and at Trinity Site each time it is open to the public. This bomb casing is very similar to the casing used on the original Fat Man atomic bomb.
The MK III bomb was built after World War II. The Fat Man bomb can be considered the "prototype" bomb for the MK III. It was changed to improve safety and reliability.
The case provided an aerodynamic envelope for the bomb. To stabilize it during free fall, the case is equipped with a 58-inch, 500 pound box tail.
It is made of 3/8 inch thick steel armor so it also provided protection to the bomb-core from anti-aircraft fire. Almost half of the weight of the bomb is in this case---about 5,000 pounds. Another 5,000 pounds of the bomb came from the high explosives which surrounded the plutonium core.
Around the middle of the casing are spots for mounting four radar antennas. The bomb was designed to explode above the ground for maximum blast effect. The radar would trigger the bomb at the prescribed altitude.
If the bomb failed to explode for some reason, it was necessary to destroy the bomb so the enemy could not learn its secrets. On the nose of the casing are places for four AN 219 destruct fuses. These would be activated on impact with the ground, igniting the high explosives in the bomb and destroy it.
It is believed about 120 MK III bombs were manufactured and stockpiled between 1947 and 1949. They were all withdrawn from the stockpile by the end of 1950.
The original Fat Man was tested at Trinity Site without a casing. The 5,000-pound bomb was placed atop a 100-foot tower to simulate an aerial blast and reduce the amount of radioactive dust spewed into the air. It had the explosive power of 20,000 tons of TNT.
Also, the bomb was not Dropped from the tower. It was sitting stationary at detonation.
Because of the height of the tower, the explosion did not create a deep crater. Most veterans describe it as a saucer-like depression about six to eight feet deep. In other words, the force of the explosion smashed or compressed the ground underneath the tower to make the crater. Like the tower itself, some of the surface was vaporized while some was sucked up into the mushroom cloud which rose from the blast.