He passed Reserve Military Aviator's test on October 20, 1917, and was commissioned First Lieutenant in January 1918, with 141st Aero Squadron.

In the second day of the St. Miheil drive with his observer, under great difficulties, carried out the longest reconnaissance over German territory of any American aviators.

As a volunteer for a mission for flying at low altitude over enemy lines for certain information, he received the Cross of War from the French.

He brought down three enemy planes and attempted to deliver messages to the famous Lost Battalion in the Meuse-Argonne Offensive, France.

[5] Chamberlin was recalled up to the military in May 1941, with the rank of Major, and stationed in charge of a training film preparation unit at Lowry Field in Denver, Colorado.