This collection consists of letters Mahan sent primarily to his daughter, Helen E. Mahan, copies of Mahan family photographs, and research notes and materials compiled by Mahan from 1897-1914 on a variety of subjects including the Spanish American War and the War of 1812. Also of note are two sets of lectures written by Mahan that he delivered at the Naval War College as well as a journal and some writings he kept while serving on the U.S.S. Iroquois in China and Japan.