The DY-500 was a class of early Earth space vehicles.

The DY-100 class received extensive design and performance reviews to become the DY-500 class. It's almost pure fission engine plant produced a clean gas exhaust who powered a MHD, providing electricity to the ship. At the moment of its commission it was one of the most popular transports. The loss of the DY-500, UNSS Courageous, was the worst tragedy in the 65 first of space exploration. (TOS reference: Star Trek Space Flight Chronology)

The DY-500 and DY-100 were similar enough in appearance that even experienced Starfleet officers were unable to tell the difference between such ships from a distance. For example, upon first encountering the SS Botany Bay, Captain James T. Kirk initally believed the ship to be a DY-500, it was Spock who correctly identified the ship as an older DY-100 type vessel. (TOS episode: "Space Seed")

In 2155, two DY-500s were involved in the First Battle of Altair VI when they attempted to intercept a Romulan fighter, but were called off by the Columbia. (ENT novel: Beneath the Raptor's Wing)

Starship classes of Earth
Arrow • Assist • Cavalry • Christopher • Cosmos • DY-100 • DY-500 • DY-700 • DY-1100-class • Daedalus • Discovery • Doppler (scout) • Edison • Galliant • Hopkins • Horizon • Intrepid (Earth) • J (freighter) • Long • Marshall • Mercury • Messier • Minuteman • NX • Poseidon • Strider • Vanguard (starship) • Verne • Y (freighter) • Yorktown • Zeus