Pre-war

Upon graduation from West Point in 1928, Seeman was appointed to the United States Army Corps of Engineers. He was first assigned cavalry duty at Fort Riley in Kansas, and was promoted to a first lieutenant on 1 December 1933. He next worked with the Nicaragua Canal Survey from 1935 to 1936, and from 1936 to 1940 he was assigned to ROTC work at Ohio State University. While working at Ohio State University, he was promoted to captain on 9 June 1938. He was promoted to major on 31 January 1941.^[1]

World War II and Manhattan Project

During World War II, Seeman was assigned to the Engineer Research and Development Laboratory at Fort Belvoir in Virginia, working as a regimental commander of the aviation engineer troops. Later in the war, he was assigned as Air Force staff in China Burma India theater. During the war he was promoted in rank. He was promoted to lieutenant colonel on 1 February 1942 and to colonel on 21 May 1943.^[1]

From 1945 to 1946, Seeman was assigned to the Manhattan Engineer District.^[1] On 3 May 1945, Major General Leslie R. Groves appointed Seeman to serve as his Army Corps of Engineers liaison at the Los Alamos Laboratory in New Mexico. As Groves' liaison, he contributed to managing efficiency at the laboratory in preparation for the Trinity test and for weapons manufacturing. On 7 August 1945, J. Robert Oppenheimer appointed him administrator of the laboratory.^[2]

During the planning for the cancelled Operation Downfall operation, Seeman reported (in response to a query about the possibility of using tactical nuclear weapons on the Japanese mainland if Japan did not surrender after the atomic bombings of Hiroshima and Nagasaki) that at least seven Fat Man-type plutonium implosion bombs would be available by X-Day, which could be dropped on Japan's defending forces. Seeman advised that American troops not enter an area hit by a bomb for "at least 48 hours". The risk of nuclear fallout was not well understood at the time, and this short time after detonation would have in actuality exposed American troops to substantial levels of radiation.^[10]

In September 1945, Seeman was made officer in charge for improvements and contstruction at Sandia Base. On October 31, 1945, he was appointed the Associate Director under Norris Bradbury (the Los Alamos Lab Director), and was made an Area Engineer responsible for the Sandia Z Division's Group Z-2 weapons assembly factory. He worked in this assignment until March 1946.^[2] In November 1945, he was made post commander at Los Alamos, a role he held until approximately September 1946.^[11] That same year, he also began working again as an aide to Groves. He witnessed the Operation Crossroads tests in the Bikini Atoll, and reported back to Groves with observations.^[12] He was designated by Groves as his representative to the National Park Service for meetings on the establishment of a monument at the site of the Trinity test.^[13]

Post-war

From 1947 to 1948, Seeman was assigned to worked with the Central Intelligence Agency (CIA).^[1] Between 1949 and 1952, he was the district engineer of the Army Corps of Engineers for the Alaska District. He oversaw the largest program of permanent construction that had ever been undertaken in Alaska up to that time.^[1] After graduating from the National War College,^[2] Seeman was assigned to the Office of the Comptroller of the Army from 1953–54.^[1]

On September 1, 1954, Seeman was appointed division engineer for the Southwestern Division of the Army Corps' Southwestern Division, headquartered in Dallas, Texas.^[1] He held this assignment until 1958.^[14] During this assignment, he additionally served as a member of the Mississippi River Commission and the Board of Engineers for Rivers and Harbors. He was promoted to brigadier general on July 14, 1955.^[1]

On 1 May 1958, Seeman was assigned to work as the chief of the construction division within the Office of the Deputy Chief of Staff for Logistics.^[1] On 1 August 1958, he was designated Director of Installations, a role he held until May 1962. While in this role, he was promoted to major general on March 10, 1959.^[1]

Seeman assumed the position of commander of Fort Leonard Wood in Missouri on May 20, 1962.^[1] He retired from the military on 30 May 1965.^[2]