Hartle graduated from St. John's College, Annapolis, Maryland, in 1910, and received a commission as a second lieutenant into the Infantry Branch of the United States Army in the same year.

[1][2] Soon thereafter, he was sent to the Philippine Islands as the American military government was still attempting to stabilize the country nine years after the end of the Philippine–American War, yet still in turmoil due in large part to the Moro Rebellion.

He returned to the Philippines in 1930, was promoted to the rank of major, and went on to Shanghai in 1932, as senior battalion commander of the 31st Infantry, under orders to protect American lives and property as the Japanese invaded China.

[2] His mission was to pull together American and Puerto Rican forces and prepare them to defend the Caribbean and eastern coast of the United States from any Axis aggression.

On August 5, 1941, Hartle was promoted to the two-star rank of major general and placed in command of the 34th Infantry Division, an Army National Guard formation, while the 34th was on maneuvers in Louisiana.

[8] Major General Hartle retired from the army with a physical disability on June 30, 1946, while living in Tyler, Texas.

The singularly distinctive accomplishments of General Hartle reflect the highest credit upon himself and the United States Army.