John Sinclair Morrison CBE (15 June 1913 – 25 October 2000) was an English classicist whose work led to the reconstruction of an Athenian Trireme, an ancient oared warship.

From Lindfield, Sussex, Morrison was educated at Charterhouse and Trinity College, Cambridge.

He was considered an expert on the Greek trireme, the oared warship of the Athenian classical golden age, and is best known as one of the founders in 1982, with Charles Willink, another classics teacher, John Coates, a naval architect, and Frank Welsh, a banker, of the Trireme Trust, to test his theories about the Athenian trireme by building a full-size reconstruction.

His elder daughter, Annis Garfield, the classicist and author, was an alumna of Girton College, and was voted the most beautiful girl in Cambridge in 1968.

[6] In 1991 he was awarded the Caird Medal of the National Maritime Museum, jointly with John Coates.