Pentagon, the, building accommodating the U.S. Dept. of Defense. Located in Arlington, Va., across the Potomac River from Washington, D.C., the Pentagon is a five-sided building consisting of five concentric pentagons connected to each other by corridors and covering an area of 34 acres (13.8 hectares). Completed in 1943, it was intended to consolidate the various offices of the U.S. War Dept., now the Dept. of Defense. One side of the vast building was damaged by a terrorist attack (Sept. 11, 2001) in which a hijacked airplane was intentionally crashed into the Pentagon. As a result of the crash and subsequent fire 189 people were killed, including the passengers and crew of the jetliner. The attack was coordinated with a similar one on the twin towers of the World Trade Center.

Pentagon Papers, government study of U.S. involvement in Southeast Asia. Commissioned by Secretary of Defense Robert S. McNamara in June, 1967, the 47-volume, top secret study covered the period from World War II to May, 1968. It was written by a team of analysts who had access to classified documents, and was completed in Jan., 1969. The study revealed a considerable degree of miscalculation, bureaucratic arrogance, and deception on the part of U.S. policymakers. In particular, it found that the U.S. government had continually resisted full disclosure of increasing military involvement in Southeast Asia—air strikes over Laos, raids along the coast of North Vietnam, and offensive actions by U.S. marines had taken place long before the American public was informed. On June 13, 1971, the New York Times began publishing a series of articles based on the study. The Justice Dept. obtained a court injunction against further publication on national security grounds, but the Supreme Court ruled (June 30) that constitutional guarantees of a free press overrode other considerations, and allowed further publication. The government indicted (1971) Daniel Ellsberg, a former government employee who made the Pentagon Papers available to the New York Times, and Anthony J. Russo on charges of espionage, theft, and conspiracy. On May 11, 1973, a federal court judge dismissed all charges against them because of improper government conduct.

Secret documents detailing the U.S. role in Indochina from World War II to 1968. The U.S. Defense Department commissioned the study; a project associate, Daniel Ellsberg, who was opposed to U.S. participation in the Vietnam War, leaked details of the documents to the press. In June 1971 The New York Times began publishing articles based on the study. The U.S. Justice Department, citing national security, obtained a temporary court order halting publication. The U.S. Supreme Court ruled that the government had failed to justify restraint of publication, and the documents were published widely, fueling debate over the country's Vietnam policy.

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