He served in a variety of command positions in the newly created air service of the United States Army and was instrumental in designing the model for what would become the commercial aviation system.

[2] On 14 June 1911, he began his studies at the United States Military Academy at West Point, New York.

He was promoted to the first lieutenant of Cavalry on 1 July 1916 and was transferred to the Big Bend District, Texas later that month.

He returned to the United States on approximately 21 May 1918 and was assigned as a member of the Air Service Control Board in the Office of the Director of Military Aeronautics in Washington, D.C. until 25 September 1918.

Cousins was a member of the advisory board, Chief Air Service in Washington, D.C., from September 1920 to August 1921.

[6] From August 1921 to June 1922, Cousins was assigned as a student officer at Yale University, where he was graduated with a Master of Science degree.

Following his graduation, he was assigned as a student officer at General Electric Company, Schenectady, New York from June 1922 through January 1923.

[6] After returning from overseas, Cousins was assigned as a student officer at the Air Corps Tactical School at Langley Field, Virginia, until 1931; he was rated as an Airplane Observer in September 1939.

[7][8][9] After graduating from the Command and General Staff School, Cousins returned to Washington, D.C. for duty in charge of National Guard aviation units with the National Guard Bureau until late in 1936; during this assignment, he received a temporary promotion to lieutenant colonel in the Air Corps on 16 June 1936 and a permanent promotion to that rank on 22 December.

Cousins was promoted to colonel in the Army of the United States on 26 June 1941 and to brigadier general on 10 July 1941.

[5] In 1955, he predicted that large gains in passenger traffic and freight shipments at Los Angeles International Airport would lead to "utter chaos" by 1960 unless improvements were made.

[16] Funeral services for Cousins were conducted at All Saints Episcopal Church, Beverly Hills, California and he was buried with full military honors, including a flyover, at Forest Lawn Memorial Park, Los Angeles.