A experimental way of cloaking starships that would not only render a ship invisible but would also alter the ship's atomic structure to allow it to pass through ordinary matter. The advantages of a phasing cloak would be immeasurable, but its development was expressly forbidden by the Treaty of Algeron, a peace accord between the Federation and the Romulan Empire. However, the Federation was covertly testing such a device aboard the U.S.S. Pegasus under the supervision of Admiral Erik Pressman. Although the phasing cloak proved itself functional by providing an escape for the U.S.S. Enterprise-D from a dangerous situation, its further use was prohibited, and Admiral Pressman was arrested and put on trial along with several others from Starfleet Intelligence.