The Bosun's Whistle is used these days only for ceremonies. They use a recording on ship board to get the crew's attention but no one has the vaguest idea what any whistle call might mean.

The modern (US) Navy chiefs are trained to use the Bosun whistle but, as I say, only for ceremonies. I have been singing at military retirement ceremonies. It's only there, and at change of command ceremonies, that I have seen them used.