Miss Mary Margaret Clifford, also known as Sister M. Lydia, was a nun who served as a nurse during the Civil War and as an Army contract nurse during the Spanish-American War at Camp Hamilton in Kentucky; Camp Conrad in Georgia; and in Matanzas, Cuba.

More than 1,500 professional nurses worked for the Army under contract during the war including nearly 250 nuns. Among the 80 black nurses who served were five nurse graduates from Tuskegee Institute. Native American nurses, including four from the Congregation of American Sisters in South Dakota, also volunteered. Many more nurses aided servicemen, both stateside and overseas, but did not sign Army contracts.

It seemed to me a wonderful thing that my country really needed me and I joyfully went, anxious only to help.
-Harriet Camp Lounsbery