The Global Positioning System (GPS) Guidance Package (GGP) Program developed an affordable, navigation-grade, miniature guidance package based on a tightly coupled, integrated combination of a Miniature GPS Receiver (MGR) and miniature Inertial Navigation System (INS) including associated processors and Adaptable Interface Unit (AIU) functions. The GGP INS used Interferometric Fiber Optic Gyroscopes (IFOGs) and micro-machined silicon accelerometers. Several key challenges were met by the GGP Program. The first key challenge and the focus of this paper is the development of the navigation grade IFOGs. These gyroscopes, with a drift requirement of less than or equal to 0.01 degree per hour, enable pure inertial navigation at or less than 1 nautical mile per hour error growth. Also, IFOGS offered the potential for low cost by avoiding the precision optics assemblies of in-production navigation grade Ring Laser Gyroscopes (RLGs). The success in producing the IFOG was greatly benefited by a companion program: the Flexible IFOG Manufacturability Program. This program involved developing machinery for automated assembly in areas such as integrated optical circuits, fiber couplers, solid state light sources and precision fiber coil winding. The successes of this program resulted in reducing fabrication time, increasing performance, increasing yield and reducing cost. For example IFOG fabrication process time for one system contractor was reduced from eight days to 12 hours by automating the coil winding. This enabled not only the timely production of gyros wound with more than 1000 meters of fiber for GGP but also enabled a lasting manufacturability legacy for future INSs.