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While reading a 1907 issue of The Marine Engineer & Naval Architect I
came across an article on underwater bells as navigation aids to
supplement fog horns or sirens.

"The idea of using water as a medium for carrying warning signals to
ships is not a new one. In 1887 patents were granted to two Americans
for submarine signalling apparatus, and in the following year the system
which is now used on all the great Transatlantic liners was closely
described in the patent applications of Messrs. Neale and Smallpage, two
Englishmen.

"Experiments have proved that the bell can be distinctly heard on board
ship, on a vessel travelling at high speed, twelve to fifteen miles from
the source of sound. In order to understand how these signals are made
available, we must first conceive a bell rung about 20 ft. or 25 ft.
below the surface. The notes do not lose their musical tone if the bell
is properly made and operated. The sounds are so much like the sound of
a bell in the air that they can be immediately recognised. A novice in
the wheel house of a ship fitted with the receivers and indicator box is
immediately able to determine the position of the bell within one
quarter of a point."

Submarine Bells, J.B. Millet (The Marine Engineer & Naval Architect,
July 1907)
https://archive.org/details/marineengineer29londuoft/page/431/mode/1up?view=theater

It's not clear how the direction was found with quarter point accuracy.

--
Paul Hirose
sofajpl.com

   

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