He also had a half-brother William Eckert, who served as a Lieutenant General in the United States Air Force and later became the fourth Commissioner of Major League Baseball.

[3] During his service in the counter-insurgency force, McClure accepted a commission as an Infantry 2nd Lieutenant in the United States Army on August 9, 1917, four months after the American entry into World War I.

Upon his return to the United States in 1920, McClure was assigned to the 19th Infantry Regiment located at Camp Sherman, Ohio, where he served as the post exchange officer.

McClure's capability as an expert horseman proved an asset to the Infantry School, and for a time he was an instructor for horsemanship at Fort Benning, leading the military base in several wins in Georgia horse show competitions.

When the United States declared war on the Empire of Japan on December 8, 1941, McClure was serving as military attaché to the American embassy in London.

Later that same year, McClure was appointed by Lieutenant General Dwight D. Eisenhower ("Ike") to chief of intelligence for the European theater of operations.

The PSYWAR framework Colonel Heber Blankenhorn and his team built to fight the Central Powers in the Great War, had been nearly forgotten through attrition and atrophy following the post-WWI drawdown.

The entity, known as the Allied Forces Information and Censorship Section (INC) was the foundation on which the U.S. psychological warfare capabilities in WWII were built.

Writing to his wife Marjory in December 1942 from "somewhere in Africa," McClure stated: My new job for which I was called by Ike very hurriedly is a continual headache ...