I’m reading Sword and Scimitar by Simon Scarrow and there’s this bit about rowers in galleys of the Knights of St. John (Malta). In the story, it is important the Knights' galley keeps silence so that they can surprise the Ottomans they are attacking just before dawn. Because of this, the rowers have corks in their mouths.
In order to ensure that none of them could shout a warning to the enemy as the galley glided towards its prey, the captains of the galleys on both sides had adopted the expedient of fitting a cork plug in the mouth of each man, held in place by leather thongs fastened by an iron shackle. It was horribly uncomfortable and suffocating once the men began to exert themselves at the oars. Thomas had seen men choke to death after some of the battles he had taken part in.
The book is fiction so I’m wondering if captains of galleys actually did this or if it’s just something the author made up to make the story more dramatic. Is there some reliable source that says this, like a book or article by a historian? I looked at Wikipedia 'Galley Slave'. It says galley slaves were treated brutally but it doesn’t say anything about corks in mouths.