[5] Promoted to lieutenant-colonel after the outbreak of the First World War in the summer of 1914, Ketcham took command of Coastal Defenses of the Delaware until 1915,[5] when he became President of the Artillery Board, stationed at Fort Monroe, position he would hold until 1917.

[1][2] During his tenure as President of the Artillery Board, Ketcham also commanded the Civilian Training Camps at Chickamauga Park, Georgia, and Plattsburgh, New York, both during the summer of 1916.

[5] At the end of his tenure, Ketcham became the first commander of Fort Story, Virginia in February 1917, ground having been broken only the previous year.

[2][7] On 19 September 1918, Ketcham took command of the 34th Brigade of the Coast Artillery Corps at Angers, France, and was promoted to brigadier-general on 1 October 1918.

[2] He would remain in France in command of the Brigade until early 1919, by which time the war was over due to the Armistice with Germany on November 11, 1918.