Robert "Bob" Martin Horn (born November 1, 1931) is an American water polo player who competed in the 1956 Summer Olympics and in the 1960 Summer Olympics.
He was born in Minneapolis.
Horn went to Fullerton College and then California State University, Long Beach playing water polo at the later location.
Horn was a member of the American water polo team which finished fifth in the 1956 tournament. He played five matches as goalkeeper.
Four year later he finished seventh with the American team in the 1960 tournament. He played four matches as goalkeeper.
For 28 years Horn was water polo coach at UCLA.