A naval flight officer (NFO) is a commissioned officer in the United States Navy or United States Marine Corps who specializes in airborne weapons and sensor systems. NFOs are not pilots (naval aviators), but they may perform many "co-pilot" or "mission specialist" functions, depending on the type of aircraft. Until 1966, their duties were performed by both commissioned officer and senior enlisted naval aviation observers (NAO). In 1966, enlisted personnel were removed from naval aviation observer duties but continued to serve in enlisted aircrew roles, while NAO officers received the newly established NFO designation, and the NFO insignia was introduced. NFOs in the US Navy begin their careers as unrestricted line officers (URL), eligible for command at sea and ashore in the various naval aviation aircraft type/model/series (T/M/S) communities and, at a senior level, in command of carrier air wings and aircraft carriers afloat and functional air wings, naval air stations and other activities ashore. They are also eligible for promotion to senior flag rank positions, including command of aircraft carrier strike groups, expeditionary strike groups, joint task forces, numbered fleets, naval component commands and unified combatant commands. A small number of US Navy NFOs have later opted for a lateral transfer to the restricted line (RL) as aeronautical engineering duty officers (AEDO), while continuing to retain their NFO designation and active flight status. Such officers are typically graduates of the U.S. Naval Test Pilot School and/or the U.S. Naval Postgraduate School with advanced academic degrees in aerospace engineering or similar disciplines. AEDO/NFOs are eligible to command test and evaluation squadrons, naval air test centers, naval air warfare centers, and hold major program management responsibilities within the Naval Air Systems Command (NAVAIR). Similarly, Marine Corps NFOs are also considered eligible for command at sea and ashore within Marine aviation, and are also eligible to hold senior general officer positions, such as command of Marine aircraft wings, Marine air-ground task forces (MAGTFs), joint task forces, Marine expeditionary forces, Marine Corps component commands and unified combatant commands. The counterpart to the NFO in the United States Air Force is the combat systems officer (CSO), encompassing the previous roles of navigator, weapon systems officer and electronic warfare officer. Although NFOs in the Navy's E-2 Hawkeye aircraft perform functions similar to the USAF air battle manager in the E-3 Sentry AWACS aircraft, their NFO training track is more closely aligned with that of USAF