Raifuku Maru, a Japanese freighter ship that allegedly "vanished" during a voyage from Boston to Hamburg, Germany, with a cargo of wheat and a crew of thirty-eight, in April 1925 (some reports erroneously say 1921 or 1924). This case is usually cited as a part of the Bermuda Triangle mystery, but in reality there has been proven to be a much more mundane explanation.

According to the popular story, the RMS Homeric, a vessel of the White Star Line, received a cryptic SOS from the Raifuku Maru on April 21st, 1925, which read, in broken English: "Danger like a dagger now! Come quick!" Reportedly, the Homeric traveled to where the vessel had given the SOS, but found not a trace of the ship. There was much speculation over what the "dagger" was (popular opinion seems to be divided between waterspouts and UFOs), and this was regarded as a genuine mystery of the sea by many. Popular writers on the Bermuda Triangle, specifically Charles Berlitz and Vincent Gaddis, propagated the myth of the vessel's "mysterious" sinking, and it entered the lexicon along with such other well-known incidents as the Mary Celeste, the Carroll A. Deering, and Flight 19.