Harold Augustin Calahan (November 7, 1889 – November 25, 1965) or H. A. Calahan was a Lieutenant Commander in the United States Navy and an author on sailing. He was born in Brooklyn and attended Columbia University for his B.S., Master He died of a heart attack in 1965 in Port Chester, New York and was buried in Arlington National Cemetery on November 30, 1965. He is known for writing the novel Back to Treasure Island (1935), a sequel to Robert Louis Stevenson's Treasure Island. He strongly argued that Stevenson had in mind to write such a story.