[4] However, he first completed the required military service and was assigned to the U.S. Army Finance Corp as a historian with the Office of the Chief of Finance in Washington, D.C.[4][5] While in the Army, he began working on a graduate degree in history at Georgetown University.
[4] From 1961 to 1964, he was the assistant executive secretary with the American Historical Association in Washington, D.C.[4] He left that position to become the director of the National Archives' survey on the Use of Original Sources in Graduate History Training.
[4] This two-year long position included conducting 600 interviews and traveling across the country to various institutions.
[4][5] Two years later, he moved to the Iowa State University where he served as chair of the history department.
[4] In the spring of 1971, he accepted the position of chair of the department of history at the University of Maryland which was a step up because it had a Ph.D.
"[4] He conducted research on a variety of topics, including archival holdings, arts of the American West, biography, military finance, research methods, teaching history, and western oil fields.
[2][5] When he died, Rendell was writing a biography of American historian Walter Prescott Webb.
[4] He joined the National Cathedral Choral Society, the University of Maryland chorus, and the choir of First United Methodist Church.