Handy deployed with the 5th Field Artillery Regiment to France in August 1917, four months after the American entry into World War I, moving to the 42nd Division in 1918.

When Company D, 168th Infantry was under severe attack in the salient du Feys, France, Major Handy voluntarily joined it upon finding that he could do so without interfering with his normal duties, and by his coolness and conspicuous courage aided materially in its success.

After graduating from the Command and General Staff School at Fort Leavenworth, Kansas, he assumed duties as Executive Officer of the 3rd Field Artillery Brigade in 1928.

He served in various staff assignments from 1929 to 1931 in Panama, then returned to Fort Sill as an instructor at the United States Army Field Artillery School until 1934.

Following the war, Handy remained Deputy Chief of Staff, and in September 1947 he assumed command of Fourth United States Army at Fort Sam Houston, Texas.