Ships in the US Navy all start with the same three letters, USS. This stands for Unites States Ship. Now here is all the wonderful information behind these three letters.

From the early beginnings of the U.S. Navy there had been no standard method of referring to U.S. Navy ships until 1907 when President Theodore Roosevelt issued Executive Order 549 on 8 January stating that all US Navy ships were to be referred to as "The name of such vessel, preceded by the words, United States Ship, or the letters U.S.S., and by no other words or letters".
Today's Navy Regulations define the classification and status of naval ships and craft:

1. The Chief of Naval Operations shall be responsible for ... the assignment of classification for administrative purposes to water-borne craft and the designation of status for each ship and service craft. ....

2. Commissioned vessels and craft shall be called "United States Ship" or "U.S.S."

3. Civilian manned ships, of the Military Sealift Command or other commands, designated "active status, in service" shall be called "United States Naval Ship" or "U.S.N.S."

4. Ships and service craft designated "active status, in service," except those described by paragraph 3 of this article, shall be referred to by name, when assigned, classification, and hull number (e.g., "HIGH POINT PCH-1" or "YOGN-8"). United States Navy Regulations, 1990, Article 0406.

This is taken from Wikipedia, sorry took the easy way out today.