The purpose of this Recommended Practice is to establish a uniform three-coordinate system for surface ships and submarines (both submerged and surfaced). This coordinate system will be used in the determination of centers-of-gravity and weight moments of inertia as they relate to the three rotational degrees of freedom, roll, pitch and yaw. It further defines the preferred origin for centers-of-gravity. There are several origin conventions in use for surface ships and submarines and this Recommended Practice defines the preferred conventions with their applicability.