CIC Detachment Activates For Manhattan Project
by Lori S. Stewart, Command Historian
U.S. Army Intelligence Center of Excellence
December 21, 2023

On 18 December 1943, a Counter Intelligence Corps (CIC) Detachment was activated to handle all aspects of security for the highly classified Manhattan Project, the United States program to develop the atomic bomb. This detachment protected the project throughout the war, ensuring neither Germany nor Japan were aware of its existence until the bombs were dropped on Japan in August 1945.

When the Manhattan Project began in August 1942, the need for security was paramount. The project had to be protected from sabotage and espionage and, equally important, the fact the U.S. was working on such a program had to be kept under wraps at all cost. Early on, a Protective Security Section (PSS) handled personnel and information security, facility protection, and security education. Maj. John A. Lansdale, of the Military Intelligence Service (MIS), acted as a liaison between the PSS and the assistant chief of staff, intelligence on the War Department General Staff.

By February 1943, a more comprehensive counterintelligence program was warranted and Capts. Horace K. Calvert and Robert J. McLeod of the CIC were assigned to the Manhattan Engineer District (MED) to organize an intelligence section under Calvert’s leadership. More CIC agents were stationed at MED sites in Oak Ridge, Tennessee; Chicago, Illinois; St. Louis, Missouri; Los Alamos, New Mexico; and Berkeley, California. In August 1943, the project transferred to the Corps of Engineers, and Calvert’s Intelligence Section merged with the PSS and moved to Oak Ridge. At this time, the newly named Intelligence and Security (I&S) Division, still under Captain Calvert’s direction, assumed responsibility for every aspect of security within the MED.

Four months later, on 18 December 1943, a CIC Detachment was organized under the I&S Division with headquarters at the Clinton Engineer Works at Oak Ridge. This detachment was responsible for all investigative responsibilities within the MED. It was authorized 25 officers and 137 enlisted agents, all hand-picked by Calvert and McLeod. Over the next year, the detachment grew to 148 officers and 161 enlisted agents. When a newly promoted Maj. Calvert was sent on a special mission to Europe in February 1944, Lt. Col. William B. Parsons took command of the I&S Division and the CIC Detachment. Maj. McLeod stayed on as Parsons’ deputy.

While the CIC Detachment headquarters was centralized at Oak Ridge, its personnel were placed on detached service in eleven branch offices around the nation. In addition to conducting investigations, the agents acted as bodyguards for the project’s scientists and monitored local rumor mills. These agents were so highly classified they were referred to by code symbols instead of names, and only the finance officer computing the pay of the agents knew their exact locations.

The dropping of the atomic bombs on Hiroshima and Nagasaki, Japan, brought an end to World War II. The CIC Detachment had done its part to protect the atomic bomb program, later called the “War’s Best Kept Secret.” In a letter of appreciation, General Leslie Groves, chief of the MED, wrote,

"The release of publicity concerning the work of this vast undertaking has evoked from the people of the world an expression of amazement that a job of such magnitude and vital interest could have been kept from the public ear. This outstanding success could not have been possible without the work performed by the Counter Intelligence Corps."

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