The United Nations Solar Fleet (abbreviated UNSF, and sometimes known as the UN Starfleet) was the organization which developed and operated Earth's exploration, transport, and military spaceships and starships in the century prior to the incorporation of the United Federation of Planets. Vessels operating under UNSF auspices generally used an identification prefix of "UNSS" before the ship's name or registry, although on some occasions, "USS" was known to be used as a variation. (TOS reference: Spaceflight Chronology; ST episode: "Star Trek Live")