USN whistle. Navy Bosun Whistle

US Navy Bosun whistle or Boatswain whistle.

This is the special metal whistle used by Navy crew members to welcome the high ranking visitors on board  and to give commands when the weather is too bad for voice commands to be heard.

It is now used mainly for ceremonial purposes.  

Used by the United States Navy (U.S.N.) and the Royal Navy (R.N.) 

Brass coloured Bosun whistle includes chain.