A method of restoring navigational performance for a moving vehicle (16, 16a, 16b) with a navigational system (30, 32) in response to a spoofed signal, the method comprising: receiving, from a Global Navigation Satellite System, GNSS, and an Inertial Navigation System, INS,, each located within the vehicle (16, 16a, 16b), a collection of data points to establish a real-time navigational route for the moving vehicle (16, 16a, 16b); determining a drift range between a planned navigational route to a predetermined destination and the real-time navigational route; determining a spoofed signal for the GNSS when the drift range is greater than a predetermined error range; characterized in that the method further comprises: disabling the GNSS when the spoofed signal is determined; determining a last known location based on the collection of data points, wherein the last known location is the point at which the real-time navigational route begins to deviate from the planned navigational route; establishing a new navigational route to the predetermined destination based on the last known location using the INS; and determining whether an accurate determining of a last known location can be established in time for a destination arrival at the predetermined destination based on the INS and at least one of navigational aids data, star tracking data, or terrain matching data; wherein, when the accurate determining cannot be established in time for the destination arrival, establishing a detour navigational route to the predetermined destination to provide time required to accurately determine the last known location or establishing a detour to an alternative destination. receiving, from a Global Navigation Satellite System, GNSS, and an Inertial Navigation System, INS,, each located within the vehicle (16, 16a, 16b), a collection of data points to establish a real-time navigational route for the moving vehicle (16, 16a, 16b); determining a drift range between a planned navigational route to a predetermined destination and the real-time navigational route; determining a spoofed signal for the GNSS when the drift range is greater than a predetermined error range; characterized in that the method further comprises: disabling the GNSS when the spoofed signal is determined; determining a last known location based on the collection of data points, wherein the last known location is the point at which the real-time navigational route begins to deviate from the planned navigational route; establishing a new navigational route to the predetermined destination based on the last known location using the INS; and determining whether an accurate determining of a last known location can be established in time for a destination arrival at the predetermined destination based on the INS and at least one of navigational aids data, star tracking data, or terrain matching data; wherein, when the accurate determining cannot be established in time for the destination arrival, establishing a detour navigational route to the predetermined destination to provide time required to accurately determine the last known location or establishing a detour to an alternative destination. disabling the GNSS when the spoofed signal is determined; determining a last known location based on the collection of data points, wherein the last known location is the point at which the real-time navigational route begins to deviate from the planned navigational route; establishing a new navigational route to the predetermined destination based on the last known location using the INS; and determining whether an accurate determining of a last known location can be established in time for a destination arrival at the predetermined destination based on the INS and at least one of navigational aids data, star tracking data, or terrain matching data; wherein, when the accurate determining cannot be established in time for the destination arrival, establishing a detour navigational route to the predetermined destination to provide time required to accurately determine the last known location or establishing a detour to an alternative destination.