John Lansdale Jr. (9 January 1912 – 22 August 2003) was a United States Army colonel who was in charge of intelligence and security for the Manhattan Project. A graduate of the Virginia Military Institute and Harvard Law School, Lansdale was commissioned as a second lieutenant in the United States Army Reserve in 1933. He was called up for active duty in June 1941, and was assigned to the Investigations Branch in the Office of the Assistant Chief of Staff, G-2 (military intelligence) of the War Department General Staff. He became involved with the Manhattan Project in 1942, eventually becoming Brigadier General Leslie Groves's special assistant for security. Lansdale coordinated the activities of the Manhattan Project's field security teams with those of other agencies such as the FBI.