Context : The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting the Army Distinguished Service Medal to Colonel (Ordnance Corps) Samuel Hof, United States Army, for exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility during World War I, first, as Commanding Officer, Frankford Arsenal, from March 1918 to March 1919, where, by his indefatigable energy, outstanding administrative ability, and thorough technical knowledge, Colonel Hof brought to a successful production basis tracer, incendiary, and armor-piercing small-arms ammunition, and supplied substantially all that was used by our troops; later as acting Chairman of the Ordnance Claims Board, where by his energy, tact, and business ability, he secured the settlement of outstanding obligation, and later, as Chief of Field Service, Ordnance Department, where he perfected the organization controlling the disposition of vast quantities of materials and plants left over from the war. 
Answer : World War I
What was the war that Samuel Hof fought in?