SARATOGA SPRINGS, N.Y. (AP) — A New York historian is giving a talk at the state Military Museum about a one-of-a-kind U.S. submarine that was so secret it was never commissioned as a Navy ship nor was it ever given a name.

Known as NR-1, the 150-foot deep-water research and engineering submarine went into duty in 1969 based out of New London, Conn. In addition to conducting covert military missions, the sub was used to carry scientists to the remote depths of the world’s oceans.