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Colonel James C. Marshall was chosen by the Chief of Engineers, Major General Eugene Reybold, to lead the Army's portion of the project in June 1942. He established a liaison office in Washington, D.C., but chose to locate his temporary headquarters in New York, on the 18th floor of 270 Broadway, where he could rely on the North Atlantic Division of the Corps of Engineers for administrative assistance.
He was allowed to recruit staff from his prior command, the Syracuse District, and he began by hiring Lieutenant Colonel Kenneth Nichols, who later served as his deputy.

Marshall collaborated with Major General Thomas M. Robbins, the director of the Corps of Engineers Construction Division, as well as Colonel Leslie Groves, Robbins' deputy, because the majority of his tasks entailed construction. Groves believed that naming the project "Development of Substitute Materials" would cause too much unwanted attention, but Reybold, Somervell, and Styer made the decision to go with that name. Marshall and Groves decided to give the Army's portion of the project the name "Manhattan District" because engineer districts often bore the name of the city in which they were situated; in this case, Manhattan. On the13th of August, Reybold issued the decree establishing the new district, making it official. It was referred to colloquially as the Manhattan Engineer District (or MED). 

Development of Substitute Materials remained as the official codename of the project as a whole, however, over time, it was surpassed by "The Manhattan Project", which is where the famous name comes from.

In retrospect, Marshall said, "I had never heard of atomic fission but I did know that you could not build much of a plant, much less four of them, for $90 million." Nichols had recently invested $128 million on constructing a single TNT facility in Pennsylvania, and additionally,

they were they satisfied with estimates to the nearest order of magnitude, which Groves compared with telling a caterer to prepare for between ten and a thousand guests. Meanwhile, a location for the manufacturing plants had been chosen by the Stone & Webster survey team. The War Production Board suggested locations near Knoxville, Tennessee, which was a remote area where the Tennessee Valley Authority could offer enough electricity and rivers could supply cooling water for the reactors. The survey team settled on a site close to Elza, Tennessee, after examining several other ones. Styer agreed to Conant's recommendation that it be acquired right away, but Marshall delayed, waiting for the outcomes of Conant's reactor studies. Only Lawrence's electromagnetic separation appeared to be far enough forward among the potential procedures to warrant starting development.

Marshall and Nichols started gathering the tools they would require. Getting the project a high priority rating was the first step. The highest ratings ranged from AA-1 to AA-4, with AAA being a special classification only given in times of emergency. Colonel Lucius D. Clay, deputy chief of staff at Services and Supply for requirements and resources, felt that the highest rating he could assign was AA-3, although he was willing to provide a AAA rating on request for critical materials if the need arose. Ratings AA-1 and AA-2 were for essential weapons and equipment only. Marshall and Nichols were dissatisfied because AA-3 was given the same priority as Nichols' Pennsylvania TNT factory. Nonetheless, this is what they had to work with at the movement.

Colonel Marshall's inability to move the project along quickly, and especially his failure to secure the Tennessee site, the Army's low priority for the project, and the location of his headquarters in New York City, infuriated Vannevar Bush. Bush expressed his concerns to the Secretary of War Harvey Bundy, as well as Generals Marshall, Somervell, and Styer, feeling that more assertive leadership was needed. He desired that the initiative be overseen by a senior policy committee and that its overall director be a distinguished officer, preferably Styer.

Groves was eventually chosen for the position by Somervell and Styer, who informed him of their choice on the17th of September. General Marshall also ordered that Groves be promoted to brigadier general because it he believed that the title "general" would be more respected by the academic scientists working on the Manhattan Project. Groves' orders moved Colonel Marshall directly under Somervell rather than Reybold, making Groves the new superior. Groves set up his headquarters in Washington, D.C. on the fifth story of the New War Department Building, where Colonel Marshall had his liaison office. On the 23th pf September, 1942, he became the Manhattan Project's director. Later that day, he joined a conference held by Stimson, at which a Military Policy Committee was formed. This committee reported to the Top Policy Group, which was made up of Bush, Styer, and Rear Admiral William R. Purnell (with Conant serving as an alternate).

Later, Groves appointed Tolman and Conant as his scientific advisors.


Four days earlier, on the 19th of September, Groves visited Donald Nelson, the War Production Board's chairman and requested broad authority to grant an AAA grade whenever necessary. Nelson initially disagreed, but when Groves threatened to approach the President, Nelson immediately changed his mindset. Groves pledged to only utilize the AAA grade when absolutely required. It quickly became apparent that the AAA rating was too high for the project's normal requirements while the AA-3 grade was too low. Groves ultimately got AA-1 authority on the 1st of July, 1944, after a prolonged fight for it. Groves claims, "In Washington you became aware of the importance of top priority. Most everything proposed in the Roosevelt administration would have top priority. That would last for about a week or two and then something else would get top priority".

Finding a director for Project Y, the team that would design and construct the bomb, was one of Groves' earliest challenges. One of the three laboratory directors, Urey, Lawrence, or Compton, was the obvious candidate, but they could not be spared. Oppenheimer was suggested by Compton because he was already well familiar with the principles of bomb design. Oppenheimer, however, lacked managerial experience and had not, unlike Urey, Lawrence, and Compton, received a Nobel Prize, which many scientists believed the director of such a significant laboratory ought to have. Many of Oppenheimer's colleagues, including his wife Kitty (Katherine Oppenheimer), his friend Jean Tatlock, and his brother Frank Oppenheimer, were, to some degree, communists, which raised questions about his security status. Groves and Nichols were persuaded during a lengthy train talk in October 1942 that Oppenheimer had a good understanding of the challenges associated with establishing a laboratory in a remote location and should be chosen as its director. On the 20th of July, 1943, Groves personally waived the security regulations and gave Oppenheimer a clearance.

Although they originally did not coordinate their activities, the British and Americans did exchange nuclear intelligence. Because it was hesitant to give up its technological advantage and assist the United States in developing its own atomic bomb, Britain rejected overtures by Bush and Conant to strengthen cooperation with its own project, code-named Tube Alloys, in 1941. Churchill treated an American scientist harshly and chose not to respond to a personal letter from Roosevelt that offered to cover all research and development costs for an Anglo-American collaboration. As a result, the United States made the decision to go it alone if their offer was declined as early as April 1942. The British, who had early in the war made substantial contributions, lacked the funding necessary to complete such a scientific program as they fought for their survival against the Nazis. Tube Alloys quickly lagged behind its American rival as a result. "We must face the fact that... [our] pioneering work... is a dwindling asset and that, unless we capitalise it quickly, we shall be outpaced, we can now actually contribute to a "merger," whereas soon we won't have much of anything," Sir John Anderson, the minister in charge of Tube Alloys, told Churchill on the 30th of July, 1942. Churchill and Roosevelt reached a loose, unwritten understanding regarding cooperation in the atomic field the same month.

An equal partnership was no longer an option, as was proven in August 1942 when the British attempted to gain significant influence over the project while bearing minimal financial responsibility. By this time, the roles of the two countries had changed from late 1941 to early 1943; in January, Conant informed the British that they would no longer get atomic information except in certain areas. C. J. Mackenzie, the head of Canada's National Research Council, was less shocked by the cancellation of the Churchill-Roosevelt agreement than the British were, writing, "I can't help feeling that the United Kingdom group [over] emphasizes the importance of their contribution as compared to the Americans." Conant and Bush notified the British that the order came "from the top".

The American scientists decided that the United States no longer required outside assistance, and they intended to stop Britain from utilizing post-war commercial applications of atomic energy, worsening the British negotiating position. Even though doing so would delay the American enterprise, the committee supported and Roosevelt agreed to limit the supply of intelligence to what Britain might utilize during the war—especially not bomb design. Early in 1943, the British ceased sending scientists and researchers to the United States, and as a result, the Americans ceased all information exchange. To get the Americans to contribute again, the British considered cutting off the supply of Canadian uranium and heavy water, but Canada needed American inputs to create them in the first place. They looked into the idea of a private nuclear program, but came to the conclusion that it would not be ready in time to influence the course of the ongoing World War II.

Conant made the decision to enlist British assistance for the project in March of 1943. The bomb design team at Los Alamos needed James Chadwick and one or two other British scientists despite the possibility of disclosing top-secret information about weapon design. The Quebec Agreement, reached by Churchill and Roosevelt in August of 1943, allowed scientists working on the same issue to resume collaboration. However, Britain consented to limitations on information regarding the construction of massive industrial facilities required for the weapon. This cooperation was furthered into the postwar era with the Hyde Park Agreement that followed in September of 1944. The Combined Policy Committee was established by the Quebec Agreement to coordinate the actions of Britain, The United Kingdom, and Canada. The American members of the Combined Policy Committee were Stimson, Bush, and Conant, the British members were Field Marshal Sir John Dill and Colonel J. J. Llewellin, whilethe Canadian member was C. D. Howe. Sir Ronald Ian Campbell, who in turn was succeeded by Lord Halifax, the British Ambassador to the United States, in early 1945, took Llewellin's seat on the committee after he returned to the UK at the end of 1943. After Sir John Dill passed away in Washington, D.C., in November 1944, Field Marshal Sir Henry Maitland Wilson took over as both the Chief of the British Joint Staff Mission and a member of the Combined Policy Committee.

Following the Quebec Agreement, the Americans' advancement and spending amazed the British. While the United Kingdom had spent roughly half a million pounds in 1943, the United States had already spent more over $1 billion (which is equivalent to $13 billion today). Chadwick gave up on any dreams of an autonomous British programme during the war and pushed for full British participation in the Manhattan Project. He made an effort to guarantee that every request for aid from Groves was granted with Churchill's support. Niels Bohr, Otto Frisch, Klaus Fuchs, Rudolf Peierls, and Ernest Titterton were members of the British Mission that landed in the United States in December of 1943. Early in 1944, more scientists began to arrive. The 35 people working under Oliphant with Lawrence at Berkeley were assigned to existing laboratory groups and the majority lasted until the conclusion of the war, while those assigned to gaseous diffusion left by the fall of 1944. The 19 dispatched to Los Alamos also joined pre-existing organizations, principally those concerned with bomb building and implosion, but not those concerned with plutonium. The Quebec Agreement included a clause stating that the United States and Britain must both agree before using nuclear weapons against another nation. Wilson consented in June 1945 for the usage of nuclear bombs against Japan to be noted as a Combined Policy Committee decision.

In order to get their hands on uranium and thorium ores on global markets, the Combined Policy Committee established the Combined Development Trust in June of 1944, with Groves serving as its chairman. The majority of the uranium in the world outside of Eastern Europe was held by the Belgian Congo and Canada, while the exiled Belgian government was located in London. Britain consented to send the majority of the Belgian ore to the United States because it was unable to utilise the majority of the supply without constrained American research. The Trust bought 1,560,000 kg of uranium oxide ore from businesses running mines in the Belgian Congo in 1944. The US Treasury Secretary Henry Morgenthau Jr. was not informed of the project because funds for the Trust were kept in a special account that was exempt from regular auditing and controls. Groves contributed a total of $37.5 million to the Trust's account between 1944 and the time of his resignation from the organization in 1947.

Groves acknowledged the importance of early British atomic research and the Manhattan Project's contributions from British experts, but he asserted that the United States could have achieved its goals without them. He added that Churchill was "the atomic bomb project's best friend because he maintained Roosevelt's interest." He would constantly rile him up by emphasizing how crucial the project was in his eyes.



Manhattan District shoulder sleeve insignia
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Colonel James C. Marshall
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General Leslie Groves notext.jpg
General Leslie Richard Groves
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General Leslie Groves (right) conferring with James Chadwick (left), the head of the British Mission.
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