The USS Pegasus (NCC-53847) was an Oberth-class Federation starship in operation during the 24th century. A prototype vessel, the Pegasus served as a testbed vehicle for various technologies, many of which would later be implemented on the Galaxy-class.
In 2358, the Pegasus was commanded by Captain Erik Pressman, and included Ensign William Riker, on his first assignment out of the Academy. In that year, the Pegasus was assigned to conduct a test of an interphase cloaking device, in direct violation of the Treaty of Algeron. During the test, an explosion occurred in Main Engineering, resulting in heavy casualties. Several members of the crew, including the first officer and chief engineer, mutinied in an attempt to shut down the illegal test. Pressman, Riker, and seven other crewmembers fled the ship in an escape pod. Not long after departing, they witnessed a large explosion in space. No wreckage was found, and the vessel was believed to have been destroyed by a warp core breach. In fact, the Pegasus was not destroyed but rather drifted in cloaked form until it re-materialized inside asteroid gamma 601 in the Devolin system.
The survivors stated that the accident in engineering had been responsible for the destruction of the Pegasus, and made no mention of the cloak. The Judge Advocate General's inquiry into the incident concluded that the surviving officers had not been entirely truthful in their recounting of the events, and suggested a further investigation. The follow-up investigation never took place, and the inquiry report was quietly buried by Starfleet Intelligence.
In 2370, the Romulan warbird IRW Terix discovered a piece of wreckage from the Pegasus in the Devolin system. Pressman, now an admiral, dispatched the USS Enterprise-D to recover the vessel first, aiming to reach the cloaking device before the Romulans discovered the Federation's duplicity. The Enterprise entered the asteroid and found the ship, which was half-buried in solid rock. The illegal events that happened aboard were made public, and Pressman, among others, were court-martialed. (TNG: "The Pegasus")