Abstract: GPS satellites broadcast GPS signals with low power transmitters less than 50 watts. Although the GPS broadcast signals are encoded using spread spectrum technology which decreases the effect noise has on the reception of the signal, jamming signals can adversely affect GPS receiver performance. Jamming signals can cause position and velocity indication within the system to be erroneous. These errors can build up within the system and the errors may take a significant time to dissipate even after the jamming signal has gone. These errors can manifest themselves as errors in velocity and errors in position on the order of tens of miles. Methods of detection of the presence of the jamming signal including observing the output of a correlator chain in which the PN code being correlated is delayed in each link in the chain are presented in this disclosure. The present disclosure also proposes countermeasures for dealing with the jamming signal.