The papers of Benjamin Delahauf Foulois (1879-1967) span the years 1898-1966, with the bulk of the items concentrated in the period 1908-1935. The collection documents Foulois's thirty-seven-year military career beginning as a soldier in the Spanish-American War and ending as chief of the Army Air Corps. It is particularly comprehensive for the World War I period and for Foulois's tenure (1927-1935) as assistant chief and chief of the Army Air Corps. The papers are arranged in five series: Diaries , Personal Correspondence , Subject File , Miscellany , and Oversize .

The diaries span the years 1898-1926 and record specific activities or tours of duty. The first diaries cover Foulois's service in Puerto Rico during the Spanish-American War and in the Philippines during the Philippine insurrection. Diaries relating to his activities in World War I supplement material on the American Expeditionary Forces in the Subject File . Typewritten transcripts accompany the handwritten diaries.

The earliest letters in the Personal Correspondence series were written to his mother by Foulois as a young soldier (1898-1905) in Puerto Rico and the Philippines. Much of the later correspondence is dated after his retirement. Included are letters from military officers, pioneer aviators, aviation writers, and historians and Foulois's detailed responses to inquiries regarding the early days of military aviation.

The largest series in the Foulois Papers, the Subject File , contains official documents relating to the different phases of his career and chronicles the development of military aviation from its beginnings in 1908 until 1935. Assigned to the office of chief signal officer of the Signal Corps in 1908, Foulois was involved in testing the first dirigible airship submitted to the army by Thomas S. Baldwin and worked with Orville and Wilbur Wright on testing the first airplane purchased by the army. Following instruction by Wilbur Wright in 1909, Foulois was sent to Fort Sam Houston, Texas, with Aeroplane No. 1 and told to learn to fly and maintain the army's only airplane. Material from this period contained in the “Aviation duty, Signal Corps” file includes a logbook for Aeroplane No. 1 and notebooks kept by Foulois.

Files on the First Aero Squadron commanded by Foulois concern training aviators and the use of planes in the Mexican Punitive Expedition of 1916-1917. Foulois served as chief of air service, American Expeditionary Forces, in World War I, and his files document the supply, training, organization, and operations of air units, his service on the Inter-Allied Aviation Committee of the Supreme War Council, and his work on the air terms of the treaty ending the war. Files from his service as commanding officer at Mitchel Field include a letter from Charles A. Lindbergh thanking him for his assistance in preparing for Lindbergh's transatlantic flight.

Issues covered during Foulois's tenure as assistant chief and chief of the Army Air Corps include organizational and war plans, research and development, the procurement of aircraft, and army airmail operations following the cancellation of contracts between the United States Post Office and commercial airlines in 1934. Also treated are his work as a member of the War Department Special Committee on the Army Air Corps (known as the Baker Board) which studied military aviation and the charges made against him during an investigation by Subcommittee Number 3 of the House of Representatives Committee on Military Affairs into profiteering in military aircraft. Foulois's activities following his retirement are documented in files on civilian defense and his civil defense work in New Jersey during World War II, his unsuccessful campaign for United States Congress, and speeches and speech notes.

Scrapbooks in the Miscellany series contain newspaper clippings and magazine articles covering Foulois's activities from 1908 to 1966, including the early days of aviation in the United States military. Other items relate to the filing scheme prepared by United States Air Force staff for Foulois's papers together with an inventory of his personal effects.