Guyots were first recognized in 1945 by Harry Hammond Hess, who collected data using echo-sounding equipment on a ship he commanded during World War II. His data showed that some undersea mountains had flat tops. Hess called these undersea mountains "guyots", because they resembled the flat-roofed biology and geology building at Princeton University, Guyot Hall, named after the 19th-century geographer Arnold Henry Guyot. Hess postulated they were once volcanic islands that were beheaded by wave action, yet they are now deep under sea level. This idea was used to help bolster the theory of plate tectonics.