Dieter Martin Gruen was born in November 1922 in Walldorf, Germany. His father was a school principal and his mother was a house wife. Gruen enjoyed physical activities and pretending to be a Native American. Gruen's family was Jewish, so when the Nazis came to power, there was an immediate effect on his family. When Jews were barred from being federal employees, his father lost his job. His father was a lieutenant in World War 1. At age 14, Gruen immigrated to the United States and stayed with family in Little Rock, Arkansas. He graduated from high school in 1939, at the age of 16. In April 1939, his parents moved to Chicago [Annotator's Note: Chicago, Illinois], so he moved there after he graduated high school. The family had nothing when they moved. His father had been in a concentration camp, but was allowed to leave. Gruen felt fortunate to escape Germany. He began college at Northwestern in 1941. He worked in a machine shop during the day and went to school at night. He was given a scholarship to continue his studies. He decided he wanted to study chemistry. Gruen followed the war in Europe very closely. He did not have any immediate family members in Germany. His brother went to America with Gruen.

Dieter Gruen graduated from Northwestern [Annotator's Note: Northwestern University in Evanston, Illinois] and was recruited to work for the Manhattan Project [Annotator's Note: code name for the American-led effort to develop an atomic bomb]. He was sent to work at Oak Ridge, Tennessee. Gruen did not know what he was getting himself into, but was told it was important war related work. He was assigned to the chemistry research division. He worked for Edward Larson [Annotator's Note: Clarence Edward Larson, American chemist and nuclear physicist]. Larson told him he was working on uranium, but was told to call it tube alloy. The British were also working on an atomic bomb. There were several other recruits there, some civilian and some in the military. He worked to separate Uranium 235 from uranium, using electromagnetic separation. Gruen had to develop chemical techniques to measure the uranium because it had never been done before. He then had to separate the separated uranium. He then had to separate the uranium from any contaminants. Gruen knew there was another plant being built at Oak Ridge [Annotator's Note: Oak Ridge, Tennessee]. Most of the separated uranium 235 that was in the bomb dropped on Hiroshima [Annotator's Note: Hiroshima, Japan] came from Gruen's plant. The Y12 [Annotator's Note: code name for Oak Ridge] plant was a huge industrial plant. Tons of uranium went through that plant. Tons of silver were borrowed from the United States Treasury to make magnets and other things needed for the project. Companies built products to the project. High school girls from the region worked at the plants and ran the machines. The project was enormous and was surprising to Gruen.

[Annotator's Note: Dieter Gruen worked as a scientist in the chemistry research division of the Manhattan Project at Oak Ridge, Tennessee.] Many of the people that came up with the idea for an atomic bomb came from German and Hungary. They ended up in the United States and Great Britain. Nuclear fission was discovered in a German laboratory. The scientist, Otto Hahn, told Otto Frisch and Lise Meitner, who then published an article about the energy produced by fission. A man named Peierls [Annotator's Note: Rudolf Peierls] realized that energy could be made into a bomb. He wrote an article about it. Frisch read the article and became friends with Peierls. They did more research on the matter, and gave a report to the British. The results were given to Churchill [Annotator's Note: Sir Winston Leonard Spencer-Churchill; Prime Minister, United Kingdom, 1940 to 1945], then to Franklin Roosevelt [Annotator's Note: Franklin Delano Roosevelt, 32nd President of the United States]. Albert Einstein had already sent a letter about it to Roosevelt. It took less than five years for a bomb to be created after the discovery of fission. Gruen believes it could have only happened in the United States. He believes that generation of American scientists were great and it could only have happened through them and the support of the American people. Gruen believes Franklin Roosevelt had a far sighted war policy. Gruen would have been inducted into the Army, but the draft board was told he should be deferred because he was a good student. After graduating, he was drafted into the Manhattan Project [Annotator's Note: code name for the American-led effort to develop an atomic bomb].

At Oak Ridge [Annotator's Note: Oak Ridge, Tennessee], there were three shifts running all the time. Dieter Gruen worked eight or nine hours a day. During his free time, Gruen liked to go into the Smokey Mountains. He liked to hike with friends. During his hikes, he would talk to his colleagues about each of their work. They figured out quickly what they were working towards. Gruen was not allowed to talk about the project to outside people. There were thousands of secret patents filed for the project. There was a fear that the Germans would make a bomb first. There were Russian spies in the project. One was a German physicist who worked for Los Alamos [Annotator's Note: Los Alamos Laboratory or Project Y, Los Alamos, New Mexicao]. He was a communist sympathizer who passed along information to the Russians.

Dieter Greun tries to talk to veterans of the war, particularly those that fought in Europe then went to the Pacific. He had found no credible evidence that Japan was going to surrender. He knew there would be a large number of American and Japanese dead. Gruen believes the atomic attacks, as bad as they were, were for the best. He understands the pros and cons of the debate. He thinks Truman [Annotator's Note: Harry S. Truman, 33rd President of the United States] made the right decision. Gruen worked in Oak Ridge [Annotator's Note: Oak Ridge National Laboratory in Oak Ridge, Tennessee] where he worked with the electromagnetic separation of uranium isotopes. Beyond that work, he did not know any other aspect of the project [Annotator's Note: the Manhattan Project; the American-led effort to develop an atomic bomb]. He did not know about bomb design or the Trinity test [Annotator's Note: nuclear bomb test at Los Alamos, New Mexico]. When Roosevelt [Annotator's Note: Franklin Delano Roosevelt, 32nd President of the United States] ran for his fourth time, it was the first time Gruen could vote. He was sad to hear about Roosevelt's death, but he continued his work. He thought the government was in good hands with Truman. Gruen was shocked when he saw the pictures of Hiroshima [Annotator's Note: Hiroshima, Japan] and Nagasaki [Annotator's Note: Nagasaki, Japan]. The destruction was unimaginable. He knew a new world was created and warfare would be different. He thought the atomic bomb should not be used again. After the war, many scientists including Gruen, formed a group that was against nuclear weapons. He published an article in a newspaper about the senate hearings following the war. Nuclear oversight was eventually given to the citizens, not the military. National laboratories around the country continued to study atomic energy after the war. Gruen was a part of that work until he retired.

After the war, Dieter Gruen heard people talked about the atomic bombs all the time. People wanted to talk about atoms and atomic energy, as if atoms had just been created. Most people did not know what to make of the new weapon, but they were happy the war was over. The scientists felt responsible and guilty for all the deaths caused by the bombs. Gruen believes that if Germany won the war, the world would be a different place. Gruen thinks the United States has been very active in stopping nuclear proliferation. Many countries were testing nuclear bombs in the atmosphere until a treaty was signed in 1960. Limitation treaties have been signed over the decades. There are much stronger bombs in the world now.