A 1932 graduate of the United States Military Academy at West Point, McCormack also studied at Hertford College, Oxford as a Rhodes Scholar, earning a Master of Arts degree in Romance languages, and at the Massachusetts Institute of Technology (MIT), where he earned a Master of Science degree in civil engineering.

On 1 July 1944, he became the Chief of the Movements Branch of Twelfth United States Army Group, remaining in this role until 28 May 1945.

In 1947, McCormack was chosen as the Director of Military Applications of the United States Atomic Energy Commission with the rank of brigadier general.

[2][3][4][5] In June 1936 he became a student at the Massachusetts Institute of Technology, from which he graduated with a Master of Science degree in civil engineering in August 1937.

[3] In October 1943, McCormack became Chief of the Transportation Branch of the First United States Army Group, and was promoted to colonel on 1 December 1943.

On 1 July 1944, he became the Chief of the Movements Branch of Twelfth United States Army Group, remaining in this role until 28 May 1945.

He was then a staff officer with the Strategy and Policy Group from 16 February until 16 August 1946, when he became chief of the Politico-Military Survey Section of the Operations and Plans Division.

For his service with the War Department General Staff, he was awarded an oak leaf cluster to his Legion of Merit on 8 April 1947.

Like most military officers, he was convinced that the men who had to use the nuclear weapons in battle needed to have experience in their proper maintenance, storage and handling.

[12] McCormack became an early advocate of the Super, which promised yields in the megaton range, and directed Norris Bradbury at the Los Alamos National Laboratory to proceed with its development even at the detriment of other weapons.

[13] The debate over the merits of the Super pitted the United States Air Force against the other services, which wanted more small, tactical weapons.

Concurrently, there was a technical debate between Teller and other scientists like Robert Oppenheimer over the feasibility of the Super, because there was no guarantee that it would work, and even after Operation Greenhouse, the processes involved in thermonuclear reactions were not fully understood.

He attended his first board meeting in Washington, DC, in his dinner jacket, having flown from Los Angeles after a speaking engagement.

[18] McCormack died at his winter home in Hilton Head Island, South Carolina, on 3 January 1975, and was buried in Arlington National Cemetery.