Military career
At the start of World War I, Lehman applied to attend a Citizens' Military Training Camp at Plattsburgh Barracks, New York. While his April 1917 application was pending, Lehman volunteered his services to the United States Navy as an expert on textiles the navy would need to acquire for uniforms and other wartime clothing and equipment. During this service, he worked closely with Franklin D. Roosevelt, then serving as Assistant Secretary of the Navy, which Roosevelt mentioned during campaign appearances when Roosevelt and Lehman were the Democratic nominees for governor and lieutenant governor in 1928.
In September 1917, Lehman was commissioned as a captain in the United States Army's Ordnance Corps. He was assigned as chief of the Ordnance Department's Equipment Section on the staff of the United States Department of War, and he was promoted to major in January 1918. Lehman subsequently served as chief of War Department's Methods Section, then chief of its Purchase Branch, and he was promoted to lieutenant colonel in October 1918.
After the end of the war in November 1918, Lehman took part in the army's demobilization as a member of the Board of Contract Adjustment, assistant director of the office of Purchase, Storage and Traffic, member of the War Department Claims Board, and chairman of the Board of Sales and Contract Termination. He was promoted to colonel in April 1919, and was discharged in June 1919. In July 1919, he was awarded the Army Distinguished Service Medal.
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 (General Staff) Herbert H. Lehman, 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. While with the Purchase, Storage, and Traffic Division of the General Staff as Chief of the Purchase Branch, member of the Board of Contract Adjustment, Chairman of the Advisory Board on Sales and Contract Termination, Member of the War Department Claims Board, and Assistant Director of Purchase, Storage, and Traffic, General Staff, Colonel Lehman's large business experience, breadth of vision, and sound judgment have been of inestimable value in formulating and in supervising the execution of the methods and policies followed in the cancellation of war contracts and obligations and in the settlement and adjustment of terminated obligations. War Department, General Orders No. 103 (July 10, 1919)
