Oswald Herbert Ernst (June 27, 1842 – March 21, 1926) was an astronomer, engineer, military educator, and career officer in the United States Army who became superintendent of the United States Military Academy. Over a forty year career, Ernst served as an engineer during Sherman's Siege of Atlanta during the American Civil War, commanded U.S. troops at Coamo during the Spanish-American War, Cuba and sat on the original commission for the Panama Canal after retirement from active service.