boatswain's call
boatswain's call is a whistle or pipe.
Also recorded as boatswain's pipe; bosun's whistle.
Overview
Pipe or a non-diaphragm type whistle used on naval ships by a boatswain.
In detail
Its recorded use is signalling whistle.
Sources
Each source is named with the standing the house places on it, so the evidence can be weighed rather than taken on trust.
reference work · Reputable secondary · Wikipedia
“Boatswain's call”, English Wikipedia, consulted as further reading
Consult the sourcereference work · Reputable secondary · Wikidata
Wikidata, structured authority record Q893187: boatswain's call
Consult the source