in the Pacific but also ushered the world into the atomic age. All life on Earth has been touched by the event which took place here.

The 51,500-acre area was declared a national historic landmark in 1975. The landmark includes base camp, where the scientists and support group lived; ground zero, where the bomb was placed for the explosion; and the McDonald ranch house, where the plutonium core to the bomb was assembled. On your visit to Trinity Site you will be able to see ground zero and the McDonald ranch house. In addition, on your drive into the Trinity Site area you will pass one of the old instrumentation bunkers which is beside the road just west of ground zero.

The Manhattan Project

The story of Trinity Site begins with the formation of the Manhattan Project in June 1942. The project was given overall responsibility of designing and building an atomic bomb. At the time it was a race to beat the Germans who, according to intelligence reports, were building their own atomic bomb.

Under the Manhattan Project three large facilities were constructed. At Oak Ridge, Tenn., huge gas diffusion and electromagnetic process plants were built to separate uranium 235 from its more common form, uranium 238. Hanford, Wash. became the home for nuclear reactors which produced a new element called plutonium. Both uranium 235 and plutonium are fissionable and can be used to produce an atomic explosion.

Los Alamos was established in northern New Mexico to design and build the bomb. At Los Alamos many of the greatest scientific minds of the day labored over the theory and actual construction of the device. The group was led by Dr. J. Robert Oppenheimer who is credited with being the driving force behind building a workable bomb by the end of the war.

The Theory

Los Alamos scientists devised two designs for an atomic bomb--one using the uranium and another using the plutonium. The uranium bomb was a simple design and scientists were confident it would work without testing. The plutonium bomb worked by compressing the plutonium into a critical mass which sustains a chain reaction. The compression of the plutonium ball was to be accomplished by surrounding it with lens-shaped charges of conventional explosives. They were designed to all explode at the same instant. The force is directed inward, thus smashing the plutonium from all sides.

In an atomic explosion, a chain reaction picks up speed as atoms split, releasing neutrons plus great amounts of energy. The escaping neutrons strike and split more atoms, thus releasing still more neutrons and energy. In a nuclear explosion this all occurs in a millionth of a second with billions of atoms being split.

Project leaders decided a test of the plutonium bomb was essential before it could be used as a weapon of war. From a list of eight sites in California, Texas, New Mexico and Colorado, Trinity Site was chosen as the test site. The area already was controlled by the government because it was part of the Alamogordo Bombing and Gunnery Range which was established in 1942. The secluded Jornado del Muerto was perfect as it provided isolation for secrecy and safety, but was still close to Los Alamos.

Building a test site

In the fall of 1944 soldiers started arriving at Trinity Site to prepare for the test. Marvin Davis and his military police unit arrived from Los Alamos at the site on Dec. 30, 1944. The unit set up security checkpoints around the area and had plans to use horses to ride patrol. According to Davis the distances were too great and they resorted to jeeps and trucks for transportation. The horses were sometimes used for polo, however. Davis said that Capt. Bush, base camp commander, somehow got the soldiers real polo equipment to play with but they preferred brooms and a soccer ball.