Each entry in WorldCat represents books by and about specific vessels. Unlike other resources in ShipIndex.org, these are books that are primarily about vessels, not just books that mention vessels. In addition, some books are "by" vessels, which means they are logs, manifests, or journals that describe voyages of the mentioned vessel.
WorldCat is a worldwide union catalog created and maintained collectively by more than 9,000 member institutions. With millions of online records built from the bibliographic and ownership information of contributing libraries, it is the largest and most comprehensive database of its kind.
Special thanks to Lorcan Dempsey and Thom Hickey for suggesting and then generating the file containing these ship Identities.