In the U.S. Navy, most Naval Aviators are "Unrestricted Line Officers" (URL), eligible for command at sea; however, a small number of Limited Duty Officers and Chief Warrant Officers are also trained as Naval Aviators. A small number of URL officers trained as Naval Aviators who hold technical degrees at the undergraduate and/or postgraduate level may also opt to laterally transfer to the Restricted Line (RL) as Aeronautical Engineering Duty Officers (AEDO). AEDOs are frequently test pilot school graduates and retain their flying status, with most of their billets being in the Naval Air Systems Command (NAVAIRSYSCOM). An even smaller number of Naval Aviators are in the U.S. Navy Medical Corps, primarily as Flight Surgeons. These are either former URL officers previously designated as Naval