After World War I, Shea became qualified as a Cavalry officer, and he carried out a variety of assignments in the Field Artillery branch, some of which included horse-drawn equipment.

Promoted to brigadier general in July 1942, Shea commanded the 141st Field Artillery Brigade during its organization and training at Camp Gordon, Georgia.

When the brigade was redesignated as the XIX Corps Artillery, Shea continued in command, and he led his unit during combat in Europe from late 1943 until the end of the war in the spring of 1945.

He served as G-3 of Eighth United States Army during its occupation of Japan and its organization and fielding of forces in South Korea during the lead up to the Korean War, and was promoted to major general in 1949.

From November 1951 to January 1953, Shea commanded the 10th Mountain Division, then a basic training unit based at Fort Riley.

[9][10] Determined to begin his military career immediately, in 1915 he enlisted as a private in the United States Army's 1st Engineer Battalion.

[11][12] In addition to serving on the Mexico–United States border during the Pancho Villa Expedition, Shea was part of a team that carried out surveys of the Atlantic coast from Brunswick, Georgia to Charleston, South Carolina.

[1] Following completion of the staff college, Shea was assigned as director of the Department of Animal Transportation at the United States Army Field Artillery School.

[5] In July 1942, Shea was promoted to brigadier general, and in August he was assigned as commander of the 90th Infantry Division Artillery, which he led during its initial organization and training.

[5] When the brigade was redesignated the XIX Corps Artillery, Shea continued in command and led the organization during its training at Camp Polk, Louisiana.

[2][5] Shea returned to the United States in June 1945 and assumed command of the War Department Personnel Center at Jefferson Barracks Military Post, Missouri.

[5] In March 1949, he was promoted to major general while serving as G-3 of Eighth United States Army during the Occupation of Japan and the command's organization and fielding of forces in South Korea during the lead up to the Korean War.

[25] In November 1949, Shea was assigned to the Presidio of San Francisco as commander of Sixth United States Army’s Central Sub-area.

[5] After briefly serving as AFF artillery inspector, from 1950 to 1951 Shea commanded the Army General School at Fort Riley, Kansas.

[26] Shea commanded the 10th Mountain Division, then a basic training unit based at Fort Riley, from November 1951 to January 1953.