Navigation systems are used to help guide ships, aircraft, and other vehicles. Two of the most common navigation systems are LORAN (Long Range Navigation) and OBOE (Operational Beacon Over-the-Horizon Entry). LORAN is a radio navigation system that uses low frequency radio signals to determine the position of a vehicle. OBOE is a radar navigation system that uses high frequency radio signals to determine the position of a vehicle. Both systems are used to help guide vehicles in areas where GPS signals are not available.