Green served with his national guard unit on Mexican Border in 1916 and was also commissioned a second lieutenant of cavalry in the Regular Army, in 1917.

During World War I, Green was promoted to the temporary rank of major and ordered to the Western Front with the 2nd Cavalry Regiment, where he served with the American Expeditionary Forces (AEF) in throughout 1918.

Subsequently, he served as Assistant Judge Advocate of the 2nd Corps at Governors Island, New York City.

Green was a lieutenant colonel at the time of the December 1941 attack on Pearl Harbor, which brought the United States into World War II.

He was than appointed an executive officer to the Military Governor of Hawaiian Islands, Lieutenant General Delos C. Emmons, and stayed in this capacity until 1943.