The Royal Navy eventually became less prominent on the River Medway as other dockyards developed and ships grew in size, so that they were largely replaced by prison hulks which would frequently dispose of their dead charges on a salt marsh at the mouth of the Swale, which was subsequently to become known as Dead Man's Island, and can still be found as such, on local maps today. The new fort and harbour developments completed at Sheerness by this time further replaced Queenborough by being better positioned at the mouth of the Medway.