The Mark 31 torpedo was a destroyer-launched acoustic torpedo developed by the Harvard and Pennsylvania State universities during World War II. A modification of the Mark 18 electric torpedo, it was conceived as an interim weapon to be used in the Pacific War until a new high-speed acoustic torpedo could be developed for the United States Navy.[1]
Further development of the torpedo was terminated due to the status of other more promising programs, notably the Mark 16 torpedo and the Mark 35 torpedo.