Global positioning system (GPS) is an important navigational device for field operations with unmanned surface vehicles (USVs) in marine environments. However, the use of GPS may not be available in some situations because GPS signals can be easily blocked by large surrounding structures and are vulnerable to natural interference and intentional jamming attacks. This study proposes an alternative navigation approach for USV operation with an onboard marine radar when the use of GPS is restricted and prohibited. Marine radar is a standard navigational sensor for a marine vehicle that can be utilized for vehicle localization in coastal areas. The surrounding coastlines can be extracted from radar measurements and the vehicle's position can be estimated by matching the obtained coastline features with a pre-built map. The performance of the proposed navigation method was assessed by a field experiment in a real coastal environment. The results are presented and discussed in this paper.