U.N.P.O.C., often written "unpoc" or "u/n/p/o/c", is an acronym for a Nineteenth Century shipping term, "unable to navigate, probably on course". The acronym was commonly used in the log books of vessels left without accurate navigational guidance, due to poor visibility and/or proximity to the North Pole. The term dropped out of common usage in the 1950s with improvements in maritime navigational aids.