Harold D. Langley has served as an archivist at the University of Pennsylvania Library and Library of Congress, then later as a diplomatic historian for the U.S. Department of State. After he received his Ph. D. degree from University of Pennsylvania, he became a history professor at The Catholic University of America. Later, he served as an associate curator of naval history at the National Museum of American History. He retired in 2000 and currently works as an independent historian.