In 2358 the USS Pegasus was lost after a mutiny over its secret test of a phasing cloak, a device banned under the Treaty of Algeron.
In 2358 Captain Erik Pressman was secretly testing a cloaking device that could also let the USS Pegasus pass through solid matter, even though the Treaty of Algeron barred the Federation from developing cloaking technology. Ensign William Riker served aboard. When the device caused an explosion, much of the crew mutinied, and Pressman, Riker and a few others escaped while the ship was thought destroyed.
In 2370 the Pegasus was found inside an asteroid. The Enterprise-D used the cloak to escape the asteroid, and Picard revealed it to the Romulans. Pressman was arrested and Riker faced an inquiry.