The S.S. Valiant is a ship in the Star Trek universe. It was mentioned in the original series episode Where No Man Has Gone Before.

Commissioned and launched in 2065, the Valiant was one of the first starships to leave Earth's solar system. It was built under the auspices of the United Earth Space Probe Agency, a predecessor organization to Starfleet. It has never actually appeared onscreen, although many fans speculate that a 'mystery ship' which appears in the opening credits of Star Trek: Enterprise might be the Valiant (the ship in question appears in the credits immediately after Zefram Cochrane's Phoenix and before the NX-01 Enterprise).

Shortly after the launch of the Valiant, it was swept off course by a spatial anomaly and found itself at the edge of the Milky Way galaxy. The ship attempted to cross the barrier which surrounded the galaxy, but was forced back when the barrier's energy interfered with ship's systems. Trouble quickly arose among the crew when several people onboard began to manifest incredible psychic powers. Things came to a head when the ship's Captain, after frantically consulting the ship's computer about the ESP abilities which were spreading among his crew, ordered the ship to self-destruct to prevent the mutated crewmembers from escaping and causing trouble throughout the galaxy.

Two centuries later, the Valiant's black box recorder marker was found by the Enterprise which had also encountered the galactic barrier. Captain Kirk consulted the logs of the Valiant in order to find out how to control a similar outbreak of ESP abilities among his own crew.