National Security Organization: A Report to Congress by the Commission on Organization of the Executive Branch of the Government, February 1949 [open pdf - 1MB]
"World conditions demand that the United States maintain a strong National Security Organization. This need results directly from the total disruption of the old balance of power among nations, and from new forms of communications and warfare which have impaired America's ocean-moated isolation. Ours is a need for defense and our military strength must be predicated upon the degree of menace which we face. At present outlook, the United States' need far a strong Military Establishment is obvious. In the past, the United States has maintained merely a nominal Army and Air Force, and its Navy has been sharply limited. The assumption was that war, and international crises which could result in war, would be rare and that there would always be ample time to build a strong military force around this permanent cadre. Now the United States, in the forefront of world affairs, must continuously deal with political and economic pressures."
U.S. Central Intelligence Agency, Freedom of Information Act: http://www.foia.cia.gov/