After graduating from West Point, Chamberlaine specialized in coastal and harbor defenses through the use of Coast Artillery.

Chamberlaine served as commander of two artillery brigades during World War I, including the Battle of Belleau Wood.

He subsequently commanded the American Expeditionary Force's Railway Artillery Reserve, including combat during the Battle of Saint-Mihiel and the Meuse-Argonne Offensive.

[2] As a board member, Chamberlaine provided advice, guidance, and recommendations to the Chief of Artillery for matters including Artillery unit task organization, personnel assignments, and equipment and weapons design, testing, acquisition, and fielding.

[1][2] On his return trip to the United States, Chamberlaine traveled by way of Europe so he could serve as an observer at the French army's annual maneuvers.

[4] Chamberlaine was promoted to major in 1910, and assigned to commanded Fort Warren, the post which provided defense for Boston Harbor.

[4] In August 1917, Chamberlaine was promoted to colonel and assigned to command the 6th Provisional Coast Artillery Regiment, which he organized, trained, and led to France.

[1][6] As a result of the contacts and relationships acquired during his previous experience in France, upon arrival, Chamberlaine was assigned as the U.S. liaison officer at the French Army's General Artillery Headquarters.

[1][6] On June 24, 1918, during the Battle of Belleau Wood, Chamberlaine's artillery units fired a 14-hour barrage in preparation for an infantry attack led by Maurice E. Shearer's 5th Marine Regiment.

[9] He was assigned as commander of the Coast Artillery Training Center at Fort Monroe, where he remained until he was posted to Hawaii as chief of staff for the Army's Hawaiian Department.