Pipe (Bos'n's), or a bos'n's call
A whistle used by Boatswains (bosuns or bos'ns) to issue commands. Consisting of a metal tube which directs the breath over an aperture on the top of a hollow ball to produce high pitched notes.
The pitch of the notes can be changed by partly covering the aperture with the finger of the hand in which the pipe is held. The shape of the instrument is similar to that of a smoking pipe.