The "Army-Navy" (AN) Fitting
AN (Army-Navy) fittings were first developed during World War II for use in military aircraft hydraulic systems which required reliable, leak-free, high-pressure hydraulic systems to operate various components such as landing gear, flaps, and control surfaces. The traditional fittings used at the time were not able to meet the rigorous demands of these applications, so a new type of fitting was needed. As a result, the AN (Army-Navy) fitting was developed to provide a robust, standardized solution that could withstand extreme pressures and temperature conditions encountered in military aviation.