Conversation so far:
where do us citizens need visas to travel
can us citizens go to the caribbean without a passport
U.S. administered territories and commonwealths do not require U.S. citizens to possess a passport for entry. In the Caribbean, Puerto Rico and the U.S. Virgin Islands fall into this category.
what are the us virgin islands
The U.S. Virgin Islands include St. Thomas, St. John and St. Croix.
do caribbean cruise passengers who are us citizens need a passport
U.S. citizens boarding a cruise ship in the U.S., then traveling to Caribbean destinations defined by the government as contiguous lands and adjacent islands, do not need a passport.

Question: what form of identification is needed
Self-contained rewrite: what form of identification is needed by caribbean cruise ship passengers who are us citizens