He attended the Wentworth Military Academy in Lexington, Missouri, and was commissioned a second lieutenant in the Marine Corps Reserve on May 21, 1917.

In June 1918, he was wounded while leading an attack on a German machine gun post during the Battle of Belleau Wood.

Ashurst returned to the United States in April 1920 and was assigned to Marine Barracks Portsmouth, New Hampshire.

He attended the advanced course at Command and General Staff College at Fort Leavenworth, Kansas, in June 1935 and served on various marine posts.

When Japan attacked the United States, Ashurst and the marines and U.S. Navy personnel under his command were captured on December 8, 1941, by Japanese forces and interned in a prisoner of war camp in Shanghai until June 1945.