Manhattan Project, the wartime effort to design and build the first nuclear weapons (atomic bombs). With the discovery of fission in 1939, it became clear to scientists that certain radioactive materials could be used to make a bomb of unprecented power. U.S. President Franklin Delano Roosevelt responded by creating the Uranium Committee to investigate this possibility. Progress was slow until Aug., 1942, when the project was placed under U.S. Army control and reorganized. The Manhattan Engineer District (MED) was the official name of the project. The MED's commanding officer, Gen. Leslie R. Groves, was given almost unlimited powers to call upon the military, industrial, and scientific resources of the nation.

A $2-billion effort was required to obtain sufficient amounts of the two necessary isotopes, uranium-235 and plutonium-239. At Oak Ridge, Tenn., the desired uranium-235 was separated from the much more abundant uranium-238 by a laborious process called gaseous diffusion. At the Hanford installation (Wash.), huge nuclear reactors were built to transmute nonfissionable uranium-238 into plutonium-239. This method was based on the principle of the self-sustaining nuclear reaction (nuclear pile) that had first been achieved under the leadership of Enrico Fermi at the metallurgical laboratory of the Univ. of Chicago. At the radiation laboratory of the Univ. of California at Berkeley costly efforts were made to separate the two uranium isotopes using cyclotrons, but only about a gram of pure uranium-235 was obtained. The actual design and building of the plutonium and uranium bombs took place at Los Alamos, N.Mex., under the leadership of J. Robert Oppenheimer. Gathered at this desert laboratory was an extraordinary group of American and European-refugee scientists.

The only nuclear test explosion, code-named Trinity, was of a plutonium device; it took place on July 16, 1945, near Alamogordo, N.Mex. The first uranium bomb ("Little Boy") was delivered untested to the army and was dropped on Hiroshima on Aug. 6, 1945, killing at least 70,000 inhabitants. On Aug. 9, 1945, a plutonium bomb virtually identical to the Trinity device was dropped on Nagasaki, killing at least 35,000 inhabitants.

Manhattan Beach, city (1990 pop. 32,063), Los Angeles co., S Calif., on Santa Monica Bay; inc. 1912. It is a residential and beach community with an oil refinery and nearby factories that produce transportation and electrical equipment, computers, and pottery. Manhattan State Beach is there.

Manhattan, indigenous people of North America of the Algonquian-Wakashan linguistic stock (see Native American languages). They were a small tribe of the Wappinger Confederacy. The Manhattan in the early 17th cent. inhabited N Manhattan Island and the east bank of the Hudson River; their principal village was on the site of present-day Yonkers, N.Y. The Dutch bought Manhattan Island from them (the sale was made final in 1626) and then practically destroyed them in the wars waged between 1640 and 1645. Thereafter they ceased to have a separate tribal existence.

Manhattan, city (1990 pop. 37,712), seat of Riley co., NE Kans., at the confluence of the Big Blue and Kansas rivers; inc. 1857. It is the trade and processing center of a farm area. Much of the economy is dependent upon Kansas State Univ. and nearby Fort Riley. The Tuttle Creek Dam and reservoir, with numerous recreational areas, is to the north. Damon Runyon was born in Manhattan.

Manhattan, borough (1990 pop. 1,487,536), 28 sq mi (57 sq km), New York City, SE N.Y., coextensive with New York co. Manhattan is the cultural and commercial heart of the city, and its dramatic skyline symbolizes New York City around the world. It is composed chiefly of Manhattan Island, and is bounded by the Hudson River on the west, New York Bay on the south, the East River on the east, and the Harlem River and Spuyten Duyvil Creek on the northeast and north. Many bridges, tunnels, and ferries link it to the other boroughs and to New Jersey. A large portion of Manhattan's workers commute to the borough every day.

Manhattan began as a town built at the tip of the island. It was called New Amsterdam and served as the capital of the colony of New Netherland during the Dutch domination. In 1664 the English captured New Netherland and renamed it New York. The boundary of New York City was first extended beyond Manhattan Island when some Westchester co. towns were annexed in 1874. In the consolidation of 1898, Manhattan became one of the five boroughs of New York City. For its history, its cultural, educational, and religious institutions, and other points of interest, see New York, city.

(1942–45) U.S. government research project that produced the first atomic bomb. In 1939 U.S. scientists urged Pres. Franklin D. Roosevelt to establish a program to study the potential military use of fission, and $6,000 was appropriated. By 1942 the project was code-named Manhattan, after the site of Columbia University, where much of the early research was done. Research also was carried out at the University of California and the University of Chicago. In 1943 a laboratory to construct the bomb was established at Los Alamos, N.M., and staffed by scientists headed by J. Robert Oppenheimer. Production also was carried out at Oak Ridge, Tenn., and Hanford, Wash. The first bomb was exploded in a test at Alamogordo air base in southern New Mexico. By its end the project had cost some $2 billion and had involved 125,000 people.

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Borough (pop., 2000: 1,537,195) of New York City, southeastern New York, U.S. It includes all of Manhattan island and three smaller islands in the East River. Bounded by the Hudson River, Harlem River, East River, and Upper New York Bay, it is said to have been purchased by Peter Minuit in 1626 from the Manhattan Indians with trinkets valued at 60 guilders. Incorporated as New Amsterdam in 1653, it was obtained by Britain in 1664 and renamed New York City. In 1898 Manhattan was chartered as one of five boroughs making up Greater New York. It is one of the world's great commercial, financial, and cultural centres. Among its many points of interest are Central Park, the Empire State Building, the site of the former World Trade Center, the United Nations headquarters, Wall Street, the Metropolitan Museum of Art, the Museum of Modern Art, Lincoln Center for the Performing Arts, Carnegie Hall, Columbia University, the Juilliard School, and New York University.

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