Skeleton Smoke Useless: use these three words

Welcome back to the daily prompts. The third for this week.

Skeleton Smoke Useless: use these three words

The dragon came at dusk. We watched from the deck, the hot boards roiling gently on a lethargic swell. Our sails hung damply limp in the breezeless tropics; notions of escape were useless.
The crew stared into the cloudless haze, weapons ready. ‘The cannon?’
‘Only if the bugger flies low.’

The dragon’s giant wings beat the air in a rhythm to match the ocean’s rise and fall, idling al...